M12 sensor junction box and sensor distribution box range from Voxintech in 4, 6, 8 and 10 port versions
by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

M12 Sensor Junction Box & Sensor Distribution Box: Complete Wiring Guide

A modern machine can carry twenty, fifty or more sensors, and every one of them needs a clean, reliable path back to the PLC. Running an individual cable from each sensor to the control panel is slow to install, expensive in cable and cable tray, and painful to fault-find. An M12 sensor junction box — also called a sensor distribution box or splitter box — solves all three problems at once. This guide explains what these boxes do, how junction boxes and distribution boxes differ, and how to choose the right port count for your machine.

M12 sensor junction box and sensor distribution box range from Voxintech in 4, 6, 8 and 10 port versions
Voxintech VXT-JB-M12 series — 4, 6, 8 and 10-port M12 sensor junction boxes and sensor distribution boxes.

What is an M12 sensor junction box?

An M12 sensor junction box is a rugged, passive connectivity hub that uses standardised M12 circular connectors to link several field devices — proximity sensors, photoelectric sensors, actuators and switches — to a single multi-core home-run cable running back to the PLC or remote I/O module.

Instead of routing dozens of individual wires through cable trays, the box is mounted close to the sensor cluster. Each sensor plugs in with a short M12 cordset, and one home-run cable does the long trip to the cabinet. The result is less cable, less labour and a far tidier machine.

Key features to look for

  • M12 quick-connect ports — tool-free sensor and actuator connection, no wire stripping
  • IP67-rated sealed housing — protection against dust, coolant, oil and washdown
  • Epoxy-resin potted body — no screw terminals to loosen under vibration
  • LED indicators per port — power and signal status visible at the machine
  • 5-pin A-coded sockets — the industry-standard pinout, accepts any brand of M12 cordset
  • PNP (sourcing) 24 V DC operation — matched to standard automation I/O
  • Wide temperature and vibration rating — suitable for real factory conditions

Benefits of using an M12 junction box

  1. Faster installation — plug-and-play M12 connectors remove manual stripping and terminal screwing, typically cutting sensor wiring time by more than half.
  2. Reduced downtime — LED indicators show at a glance which sensor has dropped out, so maintenance finds the fault at the machine instead of tracing wires in the panel.
  3. Improved reliability — sealed, potted construction resists vibration, moisture and contamination far better than a terminal strip in a small enclosure.
  4. Scalability — sensors can be added or swapped without rewiring the panel.
  5. Lower total cost of ownership — less labour, fewer wiring errors, less cable and lower maintenance cost over the life of the machine.

Common applications

  • Packaging and material handling lines
  • Automotive assembly and robot cells
  • Food and beverage processing (washdown areas)
  • CNC machine tools
  • Conveyor and sorting systems

Sensor distribution boxes: 4, 6, 8 and 10-port options

A sensor distribution box performs the same job on a larger scale: it acts as a centralised distribution point that carries power out to the field devices and signals back on one trunk cable. Port count is the main selection decision.

The Voxintech VXT-JB-M12 series is available in 4, 6, 8 and 10-port versions, each with a moulded home-run cable in 2 m, 5 m or 10 m lengths. Every port is a dual-channel M12x1 female socket, so an 8-port box carries up to 16 signals and a 10-port box up to 20 signals on a single cable. Each port also accepts an ordinary 3-wire single-signal sensor on one channel, which means one box covers both single-channel and dual-channel requirements at the same port count.

Typical distribution box specification

  • Ports: M12x1 female, A-coded, 5-pin, nickel-plated brass threads
  • Pinout: 1 = +24 V, 2 = signal B, 3 = 0 V, 4 = signal A, 5 = PE
  • Supply: 24 V DC nominal (10–30 V DC), PNP sourcing outputs
  • Current: approx. 2 A per channel, 4 A per port, 8 A per box
  • Diagnostics: 1 green power LED plus 1 yellow signal LED per channel
  • Construction: fully epoxy-potted body, gold-plated contacts, IP67 with all ports mated or capped

Benefits of a multi-port distribution box

  1. Centralised wiring architecture — one trunk cable replaces dozens of home-run cables to the PLC.
  2. Simplified maintenance — a faulty sensor is isolated and replaced without disturbing the rest of the system.
  3. Space savings — less panel clutter and far less congestion in cable trays and drag chains.
  4. Cost-efficient scaling — add sensors incrementally instead of redesigning the wiring harness.
  5. Faster commissioning — the machine builder wires to a known pinout, so the same cordsets work everywhere.

M12 junction box vs sensor distribution box: which do you need?

Feature M12 junction box Sensor distribution box
Best for Small to medium sensor groups Medium to large sensor networks
Typical port count 4–6 ports 8–10 ports
Signals carried Up to 12 (dual channel) Up to 20 (dual channel)
Ideal use case Machine-level wiring Cell or line-level distribution
Diagnostics LED per channel LED per channel
Example VXT-JB-M12-04D-05M VXT-JB-M12-10D-05M

In practice the two terms describe the same family of product. Both share the goal of simplifying cabling, reducing downtime and improving serviceability — the right choice comes down to sensor count, machine layout and how much spare capacity you want to leave for future additions. A useful rule of thumb: choose a box with at least one or two spare ports beyond today’s requirement.

Why IP67 and epoxy potting matter

Industrial environments expose wiring to dust, coolant, oil, vibration and washdown cycles. An IP67-rated M12 distribution box meets the IEC 60529 IP rating for total dust ingress protection and temporary immersion, provided every unused port is fitted with a protective cap.

Potting matters just as much as the IP rating. A box with internal screw terminals has connections that can work loose under continuous vibration, and any moisture that does get in has somewhere to sit. A fully epoxy-potted body with gold-plated contacts has no serviceable joints inside to fail, which is why potted boxes are the standard choice for welding cells, presses and high-vibration conveyor equipment.

Installation best practices

  • Mount the box as close to the sensor cluster as possible to keep cordsets short.
  • Cap every unused port — an open port destroys the IP67 rating of the whole box.
  • Use labelled or colour-coded M12 cordsets so port numbers map clearly to PLC addresses.
  • Check the supply capacity: total sensor load must stay within the per-port and per-box current limits.
  • Route the home-run cable away from VFD and motor cables to reduce electrical noise.
  • Inspect connector seals periodically in washdown and high-vibration areas.
  • Confirm sensor switching type — PNP boxes require PNP (sourcing) sensors.

Voxintech M12 junction box and distribution box range

Voxintech manufactures and supplies M12 sensor junction boxes in India and Europe across four port counts and three cable lengths:

VXT-JB-M12-10D 10-port sensor distribution box with M12 ports and status LEDs
VXT-JB-M12-10D — a 10-port sensor distribution box carrying up to 20 signals on one cable.

Frequently asked questions

What is the difference between a junction box and a distribution box?

In sensor wiring the two terms are used interchangeably. Where a distinction is made, a junction box usually groups a smaller number of sensors onto one cable run, while a distribution box handles a higher port count for centralised, cell-level wiring.

Are M12 junction boxes waterproof?

Industrial-grade M12 junction boxes are rated IP67, meaning they are protected against dust and temporary immersion — suitable for washdown areas. The rating only holds if every unused port is fitted with a sealing cap.

Can I use NPN sensors with a PNP distribution box?

No. A PNP (sourcing) box must be used with PNP sensors and PNP-configured PLC inputs. Mixing switching types will not work and can damage inputs, so always confirm the sensor type before wiring.

How many sensors can a 10-port distribution box support?

A 10-port dual-channel box supports up to 10 dual-signal devices — 20 signals in total — or up to 10 standard 3-wire single-signal sensors, all on one home-run cable.

Do these boxes need a power supply of their own?

No. Power arrives through the home-run cable from the panel and is distributed to every port, so no separate supply is needed at the machine.

Do junction boxes require a PLC to function?

No. These are passive wiring aids — they do not process logic. They simply route power out to the field devices and signals back to whatever controller you are using.

Conclusion

Whether you are wiring a single machine or a full production line, M12 sensor junction boxes and sensor distribution boxes are essential building blocks for efficient, reliable automation. They cut installation time, simplify troubleshooting and protect the sensor network from the realities of the factory floor. Choosing the right box comes down to port count, cable length and the switching type of your sensors.

Ready to simplify your sensor wiring? Explore the full Voxintech M12 junction box and sensor distribution box range to find the right fit for your application, or contact our team for help selecting a port count.

by Voxintech-admin@2022 Voxintech-admin@2022 1 Comment

Guard Locking Safety Interlock Switches: A Complete Buyer’s Guide for Indian Machine Builders

Guard Locking Safety Interlock Switches: A Complete Buyer’s Guide for Indian Machine Builders

Every machine with a moving guard door faces the same question: what stops an operator from opening that door while the hazard is still live? A standard limit switch will tell the control system that the door has opened — but by then the operator’s hand is already inside. On a machine that takes eight seconds to coast down, that is eight seconds of exposure.

A guard locking safety interlock switch solves this. It does two jobs at once: it monitors whether the guard is closed, and it physically holds the guard shut with a spring-loaded bolt until the machine has reached a safe state. Only then does the safety controller release the lock.

This guide covers everything an Indian machine builder, panel builder or maintenance engineer needs to specify the right device — locking force, locking principle, contact configuration, standards, and the mistakes that cause the most site rejections.

What is a guard locking safety interlock switch?

A guard locking interlock is a solenoid-operated safety device fitted to the leading edge of a sliding, hinged or removable machine guard. It consists of two parts:

  • The switch body, mounted on the fixed frame, containing the contact blocks, the lock bolt and the solenoid coil.
  • A coded actuator key (a “tongue”), mounted on the moving door, which enters the switch head and is trapped by the lock bolt.

When the actuator is inserted and the bolt is extended, the normally-closed safety contacts are closed and the machine is allowed to run. The bolt cannot be withdrawn until the safety relay or safety PLC energises the solenoid — and it will only do that once the stop command has been issued and the run-down or standstill condition is satisfied.

Because the actuator is a separate coded part rather than a cam or roller, the device is classified as a Type 2 interlocking device under EN ISO 14119 (adopted in India as IS 16812).

The seven specifications that actually matter

1. Locking force (retention force)

This is the pull force the lock bolt will withstand before it fails. 1300 N is the practical industry standard for machine guards, fence gates and access doors, and covers the overwhelming majority of Indian applications — power presses, injection moulding, packaging lines, CNC enclosures and robot cells.

Higher forces (2000 N and above) exist for very large, heavy or wind-loaded doors. Do not over-specify: locking force is not a safety rating, it is a mechanical rating. What matters is whether it exceeds the foreseeable force a person can apply to the door.

2. Locking principle — spring lock or solenoid lock

This is the single most important selection decision, and it is covered in detail in our dedicated article on locking principles.

  • Spring locking / solenoid unlocking (power-to-unlock): the guard stays locked when de-energised, including during a power cut. The correct choice for any machine with a run-down time.
  • Power-to-lock: the solenoid must stay energised to hold the lock, so the guard releases on power failure. Only for applications where a risk assessment demands escape on loss of supply.

For Indian conditions, where supply interruptions are routine, spring locking is almost always the right answer.

3. Contact configuration

Count your circuits before you order. A typical guard-locking device provides two separate monitoring blocks:

  • Door / actuator monitoring — tells you the guard is closed.
  • Lock (bolt) monitoring — tells you the bolt is actually extended.

A four-contact device (1NC + 1NO on each block) gives you single-channel safety with status feedback to the PLC. A six-contact device gives you dual-channel (Category 3 / 4) architecture from a single unit. Get this wrong and you will be adding a second device on site.

4. Positive opening (forced disengagement)

The NC safety contacts must be forced disengagement type — mechanically driven open, not spring-returned. Look for a stated disengagement force and travel (typically ≥80 N and ≥10 mm). Without this, the contacts can weld closed and the machine will keep running with the guard open.

5. Body format and mounting

Two formats dominate:

Format Typical size Best for
Slim tall body approx. 39 × 39 × 183 mm Fence posts, square-section frames, where you have height but not width
Compact block approx. 108 × 89 × 36 mm Shallow guard frames, sliding doors, restricted body length

Measure the frame before ordering — a body-format mismatch is the most common reason a delivered switch cannot be fitted.

6. Ingress protection and materials

IP67 with a flame-retardant PA66 housing and stainless steel internals is the working standard. A metal (rather than plastic) head is worth paying for on any door that sees impact or vibration.

7. Emergency and auxiliary release

Any door large enough for a person to enter needs a way out. Specify a front emergency unlocking knob as standard and a rear unlocking kit where the release must be operated from outside the enclosure. Ensure the unlocking knob is reset before the machine returns to service — an unreset knob leaves the guard unsecured.

Standards you will be asked about

Standard What it covers
IS 16812:2018 / EN ISO 14119 Design and selection of interlocking devices associated with guards
IS 16810 / ISO 13849-1 Safety-related parts of control systems; Performance Level (PL a–e)
EN / IEC 60947-5-1 Control circuit devices and switching elements, including positive opening
IS 16819 / ISO 12100 Risk assessment and risk reduction

An important point for buyers: the Performance Level is a property of the circuit, not of the switch. A PL e claim on a product datasheet alone is meaningless. PL is achieved through architecture, diagnostic coverage and the safety controller used — the machine builder validates it.

Common specification mistakes

  1. Using the switch as a door stop. It is a monitoring and holding device, not a mechanical end stop. Fit a separate stop.
  2. Wiring NO contacts into the safety circuit. NO contacts are auxiliary signalling only — they go to the PLC, never into the safety chain.
  3. Ignoring hinge radius. On side-hung doors, a hinge radius below about 300 mm will bind the actuator.
  4. Leaving spare actuators loose in the toolbox. A spare coded actuator is a ready-made defeat device. Control their issue and storage — EN ISO 14119 explicitly requires it.
  5. Using metal cable glands. Most plastic-bodied interlocks specify non-metallic glands to preserve the IP rating and insulation class.

Where guard locking is used in Indian industry

Power press and press brake guarding • injection moulding and blow moulding • robot and automation cells • packaging, printing and converting lines • CNC machining centres • conveyor and material handling access gates • perimeter fencing and isolation rooms • test enclosures.

If the machine has stored energy, rotating mass, or a run-down time longer than the time it takes a person to reach the hazard, guard locking is not optional — it is the control measure your risk assessment will point you to.

Ready-to-ship options from Voxintech

Voxintech stocks the Voxintech VXT-SS series of solenoid guard-locking interlocks — 1300 N locking force, 24 V DC solenoid, IP67, spring locking with solenoid unlocking, designed to EN ISO 14119 and EN / IEC 60947-5-1, with eleven interchangeable actuator keys and matching handle-and-bolt units.

  • VXT-SS-W2-D-NCNO-L-NCNO — slim tall body, 4 contacts, three M20 entries, independent door and lock circuits.
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — compact block, 6 contacts, two internally series-linked safety channels for dual-channel architecture from one device.

GST invoice on every order, delivery across India.

Request a quotation →

Frequently asked questions

What is the difference between a safety interlock switch and a guard locking switch?

A plain safety interlock switch only monitors whether the guard is closed. A guard locking switch also physically holds the guard shut until the machine is safe. If your machine has a run-down time, you need guard locking.

What locking force do I need?

1300 N covers the large majority of industrial guard doors and fence gates. Higher forces are only needed for unusually large, heavy or wind-loaded doors.

Is a guard locking interlock mandatory in India?

There is no blanket product-level mandate. The requirement comes from your risk assessment under IS 16819 / ISO 12100, read with the Factories Act duty to fence dangerous machinery. Where access is possible before the hazard has stopped, an interlock with guard locking is the recognised control.

Can I use one device for a Category 3 dual-channel circuit?

Yes, if it provides two independent NC safety channels. A six-contact device with internally series-linked door and lock contacts gives two “closed and locked” channels from a single unit.

What voltage are these switches available in?

24 V DC is the industry standard for the solenoid. Status LEDs are commonly available in 24 V DC or wide-range 10–115 V AC/DC executions.


by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

Spring Lock or Solenoid Lock? Choosing the Right Guard Locking Principle

Spring Lock or Solenoid Lock? Choosing the Right Guard Locking Principle

Two guard-locking interlocks can look identical on the shelf, carry the same 1300 N locking force and the same 24 V DC coil — and behave in exactly opposite ways the moment the power goes out. One holds the guard shut. The other lets it swing open.

Getting this choice wrong is one of the most consequential specification errors in machine safety. Here is how to get it right. For the full selection process, see our complete buyer’s guide to guard locking safety interlock switches.

The two locking principles

Spring locking with solenoid unlocking (power-to-unlock)

A compression spring drives the lock bolt into the trapped actuator. The bolt stays extended by mechanical force alone. To release the guard, the safety controller applies 24 V DC to the solenoid terminals, which retracts the bolt against the spring.

Behaviour on power failure: the guard stays locked.

Solenoid locking with mechanical release (power-to-lock)

The solenoid must remain continuously energised to hold the bolt extended. Remove the supply and the bolt retracts under spring return, releasing the guard.

Behaviour on power failure: the guard opens.

Why this matters: run-down time

Most industrial hazards do not stop the instant you press the stop button. A press flywheel, a centrifuge, a large fan, an injection screw, a robot axis under load — all continue to move after the drives are disabled. That interval is the run-down time.

If an operator can reach the hazard before the run-down finishes, the guard must remain locked for the whole of that interval. And critically, it must remain locked even if the plant loses supply during run-down, because the hazard does not stop just because the electricity did.

This is why spring locking with solenoid unlocking is the default choice for the large majority of machines, and it is a particularly important consideration in Indian plants, where supply interruptions and voltage dips are a routine part of the operating environment. A power-to-lock device in a factory with unreliable supply will release guards every time the incomer trips.

When is power-to-lock the correct choice?

Power-to-lock is not wrong — it is a specific answer to a specific risk assessment outcome. Use it where the greater risk is being trapped inside rather than reaching in, and where there is no dangerous run-down. Typical cases:

  • Walk-in enclosures and isolation rooms where personnel could be inside during a power failure, and free egress is the priority.
  • Machines with no stored energy and effectively instantaneous stopping.
  • Process rooms where emergency evacuation drives the design.

Even then, a walk-in enclosure fitted with spring locking should be provided with an escape release or a rear unlocking kit so that a person inside can always get out — that is generally the safer combination.

Side-by-side comparison

Spring locking / solenoid unlocking Solenoid locking / mechanical release
Also called Power-to-unlock, mechanical locking Power-to-lock, electromagnetic locking
Bolt held by Compression spring Energised solenoid
On power failure Guard stays locked Guard releases
Solenoid duty Energised only to release Continuously energised
Coil heating Minimal — brief energisation Continuous; expect housing temperature rise
Suits machines with run-down Yes No
Suits walk-in enclosures needing egress Only with escape release fitted Yes
Typical share of applications ~80–90% Specialist cases

The practical consequences people forget

Coil temperature. A power-to-lock device holds its coil energised for the entire production shift. A 4.8 W coil at 100% duty will raise the housing surface roughly 25 °C above ambient. In a Chennai or Ahmedabad summer, in an enclosed guard frame, that stacks up. Spring-locking devices energise only for a few seconds per door opening.

Nuisance releases. Every brownout, every generator changeover, every RCBO trip releases the guard on a power-to-lock installation. Operators stop trusting the system, and the safety relay resets become a constant irritation.

Standstill confirmation is still your job. Spring locking guarantees the guard cannot be opened without a deliberate unlock command. It does not guarantee that the machine has stopped. The unlock command must be gated by a standstill monitor, a run-down timer sized to the worst case, or a zero-speed relay. The interlock is one element of the safety function — never the whole of it.

Manual release must be reset. Both principles are supplied with a front emergency unlocking knob. After any manual unlocking operation, reset the knob before the machine returns to service. An unreset knob can prevent the bolt from engaging and leaves the guard permanently unsecured — a defect that is easy to miss on a walk-round.

How to specify it on your order

Locking principle is usually a suffix or a separate model code, not a field-settable option. It is decided at the factory. Confirm it in writing on your purchase order, and confirm it again against the rating label before commissioning.

The Voxintech VXT-SS series is supplied as standard in the spring locking / solenoid unlocking execution — the guard remains locked when de-energised, including on power failure — with a power-to-lock execution available as a catalogue variant where a risk assessment calls for it. Contact arrangement and all other technical data are identical between the two executions.

  • VXT-SS-W2-D-NCNO-L-NCNO — slim body, 4 contacts, 1300 N, 24 V DC
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — compact body, 6 contacts, dual safety channels

Check availability and pricing →

Frequently asked questions

Which is safer, spring locking or solenoid locking?

Neither is universally safer — it depends on the hazard. Spring locking is safer where reaching into a running-down machine is the risk. Power-to-lock is safer where being trapped inside is the risk. Your risk assessment decides.

What happens to a spring-locking switch during a power cut?

The lock bolt stays extended and the guard remains locked. It can only be opened with the front emergency unlocking knob or the optional rear unlocking kit.

Can I convert a spring-locking switch to power-to-lock on site?

No. The locking principle is built into the device. Order the correct execution.

Does the solenoid need to stay energised on a spring-locking device?

No. It is energised only long enough to release the bolt. Do not leave it energised while the guard is manually unlocked.

What voltage is the solenoid?

24 V DC ±10% is the standard, drawing around 200 mA / 4.8 W. Observe polarity — E1 is positive on most devices.


by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

IS 16812 and EN ISO 14119: What Indian Machine Builders Need to Know About Guard Interlocks

IS 16812 and EN ISO 14119: What Indian Machine Builders Need to Know About Guard Interlocks

Indian machine safety documentation is often written to European standard numbers, quoted to customers in ISO terms, and audited against IS numbers nobody in the room recognises. The confusion is unnecessary: the Indian standards are direct adoptions.

This article decodes the standards that govern guard interlocking devices, and translates them into decisions you actually make when specifying a switch. For the full specification process, see our complete buyer’s guide to guard locking safety interlock switches.

The standards map

Indian standard International equivalent Covers
IS 16812:2018 EN ISO 14119 Interlocking devices associated with guards — design and selection
IS 16811:2018 ISO 14120 Guards — design and construction of fixed and movable guards
IS 16810 (Part 1 & 2):2018 ISO 13849-1 / -2 Safety-related parts of control systems; Performance Levels
IS 16819:2018 ISO 12100 Risk assessment and risk reduction
IS 16818:2018 ISO 13850 Emergency stop function
IS/IEC 60947-5-1 EN / IEC 60947-5-1 Control circuit devices, positive opening operation

If your device datasheet says “designed to EN ISO 14119 and EN / IEC 60947-5-1”, it is addressing IS 16812 and IS/IEC 60947-5-1 by the same content.

The four interlocking device types

IS 16812 / ISO 14119 classifies interlocking devices by actuation principle and by whether the actuator is integral or separate.

  • Type 1 — mechanically actuated, uncoded actuator. Cam-operated position switches, hinge switches, plunger switches. The actuator is part of the guard itself.
  • Type 2 — mechanically actuated, coded actuator. Tongue-operated switches, where a separately mounted coded key enters the switch head. Almost all guard-locking interlocks fall here.
  • Type 3 — non-contact, uncoded actuator. Simple magnetic and inductive sensors.
  • Type 4 — non-contact, coded actuator. RFID-coded safety sensors.

Coding is further graded as low, medium or high level. A standard mechanical tongue actuator is low-level coded. This matters because coding level drives what additional defeat-prevention measures the standard expects you to take.

Guard locking: when the standard says you need it

The standard does not require guard locking on every guard. It requires it where either of two conditions applies:

  1. The machine’s run-down (stopping) time exceeds the access time — the time it takes a person to reach the hazard after opening the guard. Compare stopping time against approach distance calculated to ISO 13855 / IS 16815.
  2. The process itself demands the guard stay shut — for example to protect the product, contain a hazard, or prevent an interrupted cycle causing a secondary danger.

In practice, condition 1 is what catches most Indian machine builders out. A press with a heavy flywheel, a large fan, a shredder, a centrifuge or a robot carrying a load will all continue to move after stop. If the door can be opened in one second and the machine takes six seconds to stop, a plain interlock is not sufficient.

Positive opening — the non-negotiable requirement

The NC safety contacts must operate by forced disengagement (positive opening) under IEC 60947-5-1: a rigid mechanical link drives the contacts apart, so a welded or stuck contact is torn open rather than relying on a spring.

On a datasheet this appears as a stated force and travel — typically ≥80 N and ≥10 mm. If a device does not state these figures, treat it as unsuitable for a safety circuit.

Defeat prevention: Clause 7 and Annex H

IS 16812 / ISO 14119 requires that interlocking devices be designed and installed so they cannot be defeated “in a reasonably foreseeable manner”. The standard is unusually direct about this because interlock defeat is one of the most common causes of serious machine injuries worldwide.

Practical measures the standard expects:

  • Control spare actuators. A loose spare coded key in a toolbox defeats the interlock instantly. Keep spares in secure storage with controlled issue.
  • Mount out of reach or out of sight, or shield the device so the actuator entry slot cannot be accessed with a tool.
  • Fix the actuator so it cannot be removed — screws that need a special tool, welding, or one-way fasteners. Not standard hex bolts.
  • Prevent the switch or actuator being used as a door stop, which loosens fixings over time and creates the misalignment that tempts people to defeat it.
  • Monitor plausibility in the control system. Cross-check door and lock signals; flag impossible combinations.

An additional practical point: the more inconvenient a correctly working interlock is, the more likely it will be defeated. Slow unlock sequences and nuisance trips are a safety issue, not just a productivity one.

Performance Level: a property of the circuit, not the switch

This is the point most frequently misunderstood by buyers.

No interlock switch has a Performance Level on its own. PL a to PL e under IS 16810 / ISO 13849-1 is achieved by the complete safety function — sensor, logic and actuator — including architecture (Category B, 1, 2, 3, 4), diagnostic coverage, common cause failure measures and MTTFD.

  • A single-channel NC contact into a safety relay gives you Category 1 at best.
  • Two independent NC channels, correctly wired to a dual-channel safety relay with cross-fault detection, supports Category 3 and, with adequate diagnostics, Category 4 architecture.
  • Where PL e is required, EN ISO 14119:2024 points to Category 3 or 4 architecture — achievable, for example, with two Type 2 devices, or one device that itself exhibits the required category behaviour.

The machine builder validates the achieved PL. The switch supplier supplies the components and the data.

What to ask a supplier for

  1. Declared design standards (EN ISO 14119 / EN IEC 60947-5-1).
  2. Interlock type and coding level (Type 2, low-level coding, for tongue-operated devices).
  3. Forced disengagement force and travel.
  4. Mechanical and electrical life figures.
  5. Third-party certification and CE marking documentation — for example TÜV SÜD series-level certification, certificate available on request.
  6. Locking force and locking principle.
  7. Contact configuration and internal link arrangement.

Compliant devices available in India

The Voxintech VXT-SS series is designed to EN ISO 14119 and EN / IEC 60947-5-1, classified as Type 2 with a coded tongue actuator, with forced-disengagement NC contacts rated ≥80 N / ≥10 mm, 1300 N locking force and IP67 protection.

  • VXT-SS-W2 series — 4 contacts, independent door and lock circuits, three M20 entries
  • VXT-SS-W5 series — 6 contacts, two internally series-linked safety channels for Category 3 / 4 architecture from one device

Request datasheets and certificates →

Frequently asked questions

Is IS 16812 mandatory in India?

IS 16812 is a voluntary standard, but it is the recognised good practice referenced in machine safety specifications, and it is routinely written into tender and OEM supply contracts. The underlying legal duty comes from the Factories Act requirement to securely fence dangerous machinery.

Is IS 16812 the same as ISO 14119?

Yes — IS 16812:2018 is the Indian adoption of the ISO 14119 content on interlocking devices associated with guards.

Does my interlock switch need BIS certification?

Guard interlock switches are not currently covered by a BIS Compulsory Registration Scheme category in the way that, for example, SMPS units are. Confirm the current QCO position for your HS code at the time of import, as the regulatory list changes.

What is a Type 2 interlocking device?

A mechanically actuated device with a separate coded actuator — the tongue-operated safety switches used for guard locking.

Can one device give me Category 3?

It can support Category 3 if it provides two independent NC safety channels wired to a dual-channel safety relay. The category is a property of the whole circuit.


by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

How to Wire a Guard Locking Safety Switch to a Safety Relay

How to Wire a Guard Locking Safety Switch to a Safety Relay

A guard locking interlock has more terminals than most panel builders expect — four to six contacts, a solenoid coil and an indicator circuit. Wire them in the wrong roles and you either lose the safety function entirely or spend a day chasing a relay that will not reset.

This is the practical wiring sequence, the terminal logic behind it, and the mistakes that cause commissioning failures. For device selection, see our complete buyer’s guide to guard locking safety interlock switches.

Note: this article is general guidance. Always work from the wiring label fitted to the specific switch and the machine’s own safety design documentation. Installation and commissioning must be carried out by competent personnel.

Understand the four circuit groups first

Every solenoid guard-locking interlock separates into four functional groups:

Group Typical terminals Role
Door / actuator monitoring NC 11-12, 21-22 Safety circuit — closed only when the actuator key is fully inserted
Lock (bolt) monitoring NC 41-42, 51-52 Safety circuit — closed only when the lock bolt is extended
NO status contacts 33-34, 43-44, 63-64 Auxiliary signalling to the PLC only — never part of a safety function
Solenoid coil E1 (+) / E2 (−) 24 V DC unlock command from the safety controller
Status indicator O1 / O2 Local LED, commonly 24 V DC or 10–115 V AC/DC wide range

Terminal numbering varies by model. Confirm against the label before you strip a single core.

Step 1 — Decide your architecture

Single channel (Category 1 class): put one door NC and one lock NC in series into a single safety relay input. The relay only sees a closed circuit when the guard is both closed and locked. Simple, but a single fault can defeat it.

Dual channel (Category 3 / 4 class): you need two independent “closed and locked” channels feeding the two inputs of a dual-channel safety relay with cross-fault detection.

Two ways to achieve this:

  • Four-contact device with independent circuits: wire door NC into channel 1 and lock NC into channel 2. This evaluates the two functions separately, which is what you want when the control system must distinguish “closed” from “locked” independently — but check your safety design, since each channel then monitors only one function.
  • Six-contact device with internal series links: some compact devices cross-link the blocks internally (e.g. terminal 12 to 41, and 22 to 51), so each pair forms a complete series “door closed and locked” channel available at 11-42 and 21-52. Both relay inputs then see the full guard condition, giving you dual-channel architecture from a single device.

Where independent door and lock circuits are required by the safety design, choose the slim-body four-contact format; where you want two complete safety channels from one unit, choose the six-contact cross-linked format.

Step 2 — Wire the safety channels

  1. Take the two NC safety channels to the dual-channel inputs of the safety relay (typically S11/S12 and S21/S22 — check your relay).
  2. Keep the two channels in separate cores of the same multicore or in separate looms where the risk assessment calls for it, so a single crush cannot short both.
  3. Do not fuse or switch anything into the safety channels other than the interlock contacts.
  4. Use the relay’s cross-fault monitoring if it has it; that is what buys you Category 3.

Step 3 — Wire the NO status contacts to the PLC

The NO contacts close when the actuator is withdrawn (guard open) and when the lock bolt retracts (unlock confirmation). Take them to standard PLC digital inputs. Use them for:

  • HMI status display — “guard open”, “lock released”
  • Interlock plausibility checks (flag impossible combinations such as bolt extended with actuator withdrawn)
  • Production logging and cycle interlocks

They must never be wired into the safety chain. They are not forced-disengagement contacts.

Step 4 — Wire the solenoid correctly

  • Observe polarity. On most devices E1 is positive, E2 negative. Reversed polarity will not release the bolt.
  • Drive E1/E2 from a safety relay output or safety PLC output, not from a plain PLC output. The unlock command is itself a safety-relevant signal.
  • Gate the unlock command behind the run-down or standstill condition: stop request → drives disabled → standstill monitor satisfied → relay energises E1/E2 → bolt releases.
  • Fit a suppression diode if your relay contact requires it, and check the coil’s rated current (commonly around 200 mA / 4.8 W at 24 V DC).
  • Do not leave the solenoid energised while the guard is manually unlocked.

Step 5 — Wire the indicator

The LED terminals are independent of the safety circuits. On wide-range executions they accept 10–115 V AC/DC, which lets you drive the lamp from a convenient panel supply. On standard executions they expect 24 V DC at low current.

Step 6 — Function test before release to production

Verify each state on the machine, not on the bench:

Condition Door NC Lock NC Door NO Lock NO
Guard closed and locked Closed Closed Open Open
Guard closed, unlock commanded Closed Open Open Closed
Guard open, solenoid energised Open Open Closed Closed
Guard open, solenoid de-energised Open Closed Closed Open
Emergency manual unlock operated Closed Open Open Closed

Confirm that the machine cannot be started in any state except the first row, and that opening the guard mid-cycle produces a stop.

Five wiring mistakes that fail commissioning

  1. NO contacts in the safety circuit. The relay will appear to work and the machine will run with the guard open.
  2. Solenoid driven from a standard PLC output. A software fault or output failure can release the guard.
  3. Unlock command not gated by standstill. The bolt releases while the machine is still running down.
  4. Metal cable glands on a plastic-bodied switch. Compromises the insulation class and the IP67 seal.
  5. Actuator entry gap out of tolerance. Most devices want a ready position of 1.0–3.5 mm and alignment within ±1 mm of the slot centre. Outside that, you get intermittent contacts and a relay that will not reset.

Devices and matching safety relay

The Voxintech VXT-SS series provides both wiring approaches, plus a matching 24 V DC dual-channel safety relay module.

  • VXT-SS-W2-D-NCNO-L-NCNO — independent door and lock circuits, three M20 entries for left/right/bottom cable routing
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — internally cross-linked, two complete series safety channels at 11-42 and 21-52
  • VXT-SR-24 — dual-channel safety relay module for guard monitoring and unlock control

Get a wiring drawing with your quotation →

Frequently asked questions

Can I wire the door and lock NC contacts in series?

Yes — that is the standard single-channel approach, and it means the machine can only run when the guard is both closed and locked. For dual-channel Category 3 you need two independent such channels.

Which terminals go to the safety relay?

Only the forced-disengagement NC contacts. On most devices these are the 11-12 / 21-22 door contacts and the 41-42 / 51-52 (or 21-22) lock contacts, depending on model.

What voltage does the solenoid need?

24 V DC ±10% is standard, typically around 200 mA. E1 is normally positive — check the label.

Do I need a safety relay, or can I use a safety PLC?

Either. A safety PLC gives you more diagnostics and easier plausibility checking; a dedicated dual-channel safety relay is simpler and cheaper for a single guard.

Why won’t my safety relay reset after closing the guard?

Most commonly the actuator entry gap or alignment is out of tolerance, so one NC contact is not fully making. Check the 1.0–3.5 mm ready position and ±1 mm alignment, then check for an unreset emergency unlocking knob.



by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

Safety Interlock Switch Price in India: What You Should Expect to Pay


Safety Interlock Switch Price in India: What You Should Expect to Pay

“What’s the price of a safety interlock switch?” is a question with a ten-times spread in the answer. The same nominal function — 1300 N locking force, 24 V DC solenoid, IP67 — can be quoted at wildly different numbers depending on brand origin, contact count and who is in the supply chain.

This guide explains what actually drives the cost, so you can compare quotes on a like-for-like basis instead of on the headline number. For specification help, see our complete buyer’s guide to guard locking safety interlock switches.

Indicative price bands (India, 2026)

Category Typical configuration Indicative price per unit
European premium brands 4–6 contacts, 1300–2000 N, metal head [₹ INSERT]
Japanese / global automation brands 4–5 contacts, 1300 N [₹ INSERT]
Value-engineered imported brands 4–6 contacts, 1300 N, IP67 [₹ INSERT]
Actuator keys (ordered separately) Straight, angled or adjustable [₹ INSERT]
Handle and bolt units Zinc or aluminium alloy [₹ INSERT]
Dual-channel safety relay module 24 V DC [₹ INSERT]

Prices exclude GST and are indicative only. Volume, configuration and lead time all move the number.

The eight things that actually move the price

1. Contact count

A four-contact device (1NC+1NO door, 1NC+1NO lock) is the volume item. A six-contact device costs more but can replace two devices where dual-channel architecture is required — often the cheaper installed solution.

2. Locking force

1300 N is the volume standard and the best value point. 2000 N and above carries a significant premium and is unnecessary for most guard doors.

3. Head material

A metal head resists impact, vibration and heat far better than a plastic head, and costs more. On a door that gets slammed a hundred times a shift, it pays for itself in a year.

4. Locking principle

Spring locking with solenoid unlocking (guard stays locked on power failure) and power-to-lock executions are usually priced the same. Power-to-lock is often a made-to-order variant with a minimum order quantity, which affects your effective cost.

5. Cable entry configuration

Three M20 entries (left, right, bottom) give you routing flexibility on awkward frames. A single bottom entry is cheaper but constrains the installation. Pre-wired cable versions carry a premium and a longer lead time.

6. Certification and documentation

CE marking, third-party series certification (for example TÜV SÜD), declared forced-disengagement figures and a full technical datasheet all carry real cost. A cheaper unit that cannot produce these documents will fail a customer safety audit — and a failed audit costs more than the switch.

7. Accessories are separate line items

This is where quotes diverge most. The switch body is normally supplied without an actuator. Budget for:

  • One actuator key per door (straight, angled, cushioned or adjustable)
  • A handle-and-bolt unit where the door needs an escape-safe access point
  • A rear unlocking kit where release is needed from outside the enclosure
  • A safety relay module

A quote that looks 30% cheaper often simply excludes the actuator.

8. Channel depth

Every step between the factory and your panel adds margin. Buying from an importer-distributor rather than through a sub-dealer typically removes one or two layers.

How to compare two quotes fairly

Build the comparison on a per-door basis, not per-part:

Line item Quote A Quote B
Switch body (locking principle, contact config)    
Actuator key (type)    
Handle / bolt unit if required    
Rear unlocking kit if required    
Safety relay share    
Freight and packing    
GST    
Delivered cost per guard door    
Lead time (ex-stock or import?)    
Certification pack included?    
Spares and replacement availability    

Then ask the two questions that decide it: can they ship from stock in India, and can they supply the same part again in eighteen months when you need a replacement?

The hidden cost nobody quotes for

A guard interlock that arrives in eight weeks from Europe is not a bargain when your commissioning is next Tuesday. Nor is a device whose replacement is unavailable when it fails in year three, forcing a redesign of the guard mounting.

For most Indian OEMs and end users, the practical sweet spot is a well-documented, properly certified device held in stock in India, with the actuator range and accessories available from the same source.

Value-engineered guard locking from Voxintech

The Voxintech VXT-SS series is positioned for exactly that gap — full 1300 N locking force, 24 V DC solenoid, IP67 flame-retardant PA66 body with stainless internals, metal rotatable head, forced-disengagement NC contacts, designed to EN ISO 14119 and EN / IEC 60947-5-1, held in stock in India.

  • VXT-SS-W2-D-NCNO-L-NCNO — slim tall body, 4 contacts, 3 × M20 entries
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — compact body, 6 contacts, dual safety channels

Eleven interchangeable actuator keys, five handle-and-bolt units, rear unlocking kit and matching safety relay all available from the same catalogue. GST invoice on every order, delivery across India.

Get today’s price for your configuration →

Frequently asked questions

Why do safety interlock switch prices vary so much?

Brand origin, contact count, locking force, head material, certification depth and whether the actuator is included. A quote without the actuator is not comparable to one with it.

Is the actuator key included with the switch?

Usually not. Guard locking switches are normally supplied as a body only, and the actuator is selected to suit the door construction and approach direction.

Does GST apply?

Yes. Prices are typically quoted ex-GST; confirm the applicable rate and HSN code on your invoice. GST invoicing lets you claim input tax credit.

Do I need one switch per guard door?

One interlock per access point, yes. Large enclosures with multiple doors need one at each door, with the channels wired in series or evaluated individually.

Can I get bulk or OEM pricing?

Yes — machine builders buying in repeat volumes should ask for annual-rate contract pricing rather than one-off quotes.


by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

Power Press Safety: Why Guard Locking Interlocks Are Not Optional

Power Press Safety: Why Guard Locking Interlocks Are Not Optional

The power press is the machine that has cost Indian industry more fingers and hands than any other. Ludhiana, Faridabad, Rajkot, Coimbatore, Pune — every press cluster carries the same injury pattern, and the same root cause: someone reached into the die area while the machine still had energy in it.

The gap between “the guard is open” and “the machine has actually stopped” is the entire problem. A guard locking interlock closes that gap. For device selection, see our complete buyer’s guide to guard locking safety interlock switches.

Why a plain interlock is not enough on a press

A mechanical power press stores enormous rotational energy in its flywheel. When the operator hits stop, the clutch disengages — but the flywheel keeps spinning, and depending on the machine, the brake condition and the tooling, the slide can continue to move.

Compare two numbers:

  • Access time: how long it takes a hand to travel from the opened guard to the die area. Often well under one second.
  • Stopping (run-down) time: how long it takes for all hazardous motion to cease. Frequently several seconds on an older or poorly maintained press.

Where stopping time exceeds access time — which is the normal case on presses — IS 16812 / EN ISO 14119 points to guard locking: the guard must be held physically closed until standstill is confirmed.

A plain position switch tells you the guard opened. It does not stop the hand.

The specification for press shop conditions

Press shops are hostile environments: oil mist, slug and scrap, continuous vibration, doors slammed by operators under piece-rate pressure, and ambient temperatures that punish plastic parts. Specify accordingly.

Requirement Why it matters on a press
Spring locking / solenoid unlocking The guard must remain locked during a power cut. The flywheel does not stop because the supply did.
1300 N locking force minimum Operators lean on and pull at guard doors. The bolt must hold.
Metal rotatable head Survives impact and vibration; four entry directions let you match the door approach without redesigning the frame.
Forced disengagement NC contacts (≥80 N / ≥10 mm) Contacts are torn open even if welded — essential where a stuck contact means a stroke with the guard open.
IP67, PA66 body, stainless internals Oil mist, coolant and slug debris.
Cushioned actuator key Rubber-cushioned “D” type actuators absorb door slam and vibration, dramatically extending life.
Mechanical life > 1,000,000 operations A press guard on a high-cycle job opens hundreds of times per shift.

Mounting the interlock on a press guard

  1. Fit a separate mechanical door stop. Never use the switch or actuator as the end stop — this is the single most common installation fault, and it destroys alignment within weeks.
  2. Set the actuator entry gap to the specified ready position, typically 1.0–3.5 mm, with alignment within ±1 mm of the slot centre.
  3. Fix the actuator so it cannot loosen. Screws with a tamper-resistant head, or welding. Vibration will back out a standard bolt.
  4. Choose the body format to suit the frame. A slim tall body (around 39 × 39 × 183 mm) fits fence posts and square section frames; a compact block (around 108 × 89 × 36 mm) suits shallow guard frames and sliding doors where there is no room for a tall body.
  5. Route cables away from the slug chute and scrap path.
  6. Fit an emergency unlocking knob and, where the operator can be inside the guarded area, a rear unlocking kit so escape is always possible.

Wiring it into the press control

The unlock command must be gated by a genuine standstill condition, not a timer somebody guessed at:

Stop request → clutch disengaged and brake applied → standstill / zero-speed monitor satisfied → safety relay energises the solenoid → bolt retracts → operator opens the guard.

Where the press has no standstill monitor, use a run-down timer set from the measured worst-case stopping time on that specific machine, remeasured after brake maintenance. Brake wear lengthens run-down; a timer set on a new brake becomes unsafe on a worn one.

Wire the NC safety contacts into the safety relay. Use the NO contacts for PLC status only.

Defeat is the real failure mode

Press operators on piece rate will defeat a guard that slows them down. A spare actuator key left in a drawer is all it takes.

  • Keep spare actuators in secure, controlled storage.
  • Mount the switch where the entry slot cannot be reached with the door open.
  • Use the control system to flag impossible signal combinations — for example, actuator inserted while the door limit says open.
  • Fix the productivity problem, not just the interlock. If the unlock sequence takes fifteen seconds, someone will find a way around it.

The Factories Act angle

Section 21 of the Factories Act requires that dangerous parts of machinery be securely fenced. State factory inspectorates increasingly expect that fencing on presses to be interlocked, and where run-down exists, interlocked with guard locking. A documented risk assessment to IS 16819 / ISO 12100 showing why guard locking was or was not applied is the paperwork an inspector will ask for.

Guard locking interlocks in stock

The Voxintech VXT-SS series is built for exactly this duty: 1300 N locking force, spring locking with solenoid unlocking so the guard stays locked on power loss, metal rotatable head, IP67, forced-disengagement contacts, mechanical life over one million operations, designed to EN ISO 14119 and EN / IEC 60947-5-1.

  • VXT-SS-W2-D-NCNO-L-NCNO — slim tall body for fence posts and frames
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — compact body for shallow frames and sliding guards, six contacts

Cushioned and adjustable actuator keys, handle-and-bolt units and a matching 24 V DC safety relay available from the same range.

Talk to us about your press guarding →

Frequently asked questions

Does every power press need a guard locking interlock?

Not every one — it depends on the risk assessment. But wherever the stopping time exceeds the time it takes to reach the die area, guard locking is the recognised control.

Can I use a plain limit switch on a press guard?

Only where hazardous motion stops before a person can reach it. On a flywheel press that is rarely the case.

What locking force do I need for a press guard?

1300 N is the standard and is adequate for the large majority of press guard doors and fence gates.

How do I know my run-down time?

Measure it on the specific machine, with the tooling fitted, after the brake has been serviced — and re-measure periodically. Do not take it from the machine manual.

What if the power fails while the press is running down?

With a spring-locking (power-to-unlock) device the guard stays locked. This is the correct behaviour for presses and the reason power-to-lock devices are unsuitable here.


by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

Choosing the Right Actuator Key for a Guard Locking Safety Switch

Choosing the Right Actuator Key for a Guard Locking Safety Switch

Here is a scenario that plays out on Indian shop floors every week. The interlock switches arrive, the panel builder unpacks them, and there is no actuator in the box. The line is due to run on Monday. Somebody improvises with a flat strip of steel — and the interlock is now defeated by design.

Guard locking switches are almost always supplied as a body only. The actuator is a separate order line, and it is not a trivial one: the wrong actuator geometry will bind, misalign, wear out prematurely, or simply refuse to enter the head.

This guide covers how to pick correctly the first time. For device selection, see our complete buyer’s guide to guard locking safety interlock switches.

What the actuator actually does

The actuator — often called the tongue or key — is a coded metal blade fixed to the moving guard. When the door closes, it enters a slot in the switch head, operates the contact mechanism and is then trapped by the lock bolt.

Because it is a separate, coded part, the device qualifies as a Type 2 interlocking device under IS 16812 / EN ISO 14119. That coding is what stops a screwdriver or a cable tie from operating the switch.

The four decisions

1. Door type and approach direction

Door type Actuator geometry
Sliding door, straight approach T-shaped straight — the actuator travels in line with the slot
Hinged door, right-angle approach L-shaped — the blade turns through 90° to enter the slot
Deep frame or offset mounting Long T-shaped or long L-shaped — extra reach across the gap
Awkward geometry, unknown at design stage Adjustable — approach angle trimmed on site
Compound or multi-axis approach Multi-axis rotating head type

Combine this with the switch head, which on most quality devices rotates to four entry positions. Between head rotation and actuator geometry you can usually solve any door layout without modifying the frame.

2. Cushioned or rigid

Cushioned actuators (usually designated with a “D” suffix) carry rubber bushes that absorb door impact and vibration.

Specify cushioned wherever:

  • The door is slammed rather than closed
  • The machine vibrates continuously — presses, hammers, vibratory feeders
  • The guard is large and gains momentum
  • The door is on a high-cycle application

The cushion protects both the actuator and the switch head, and it is a small premium against a switch that fails in six months.

3. Hinged doors: check your hinge radius

On a side-hung door the actuator swings through an arc. If the hinge radius is too tight, the actuator will not track the slot and will bind or shear.

A hinge radius greater than 300 mm is the usual minimum. Below that, either move the switch further from the hinge, or use an adjustable or multi-axis actuator designed for tight arcs.

4. Alignment and gap

Two numbers to hold to at installation:

  • Ready position (gap between actuator and head face): 1.0–3.5 mm.
  • Alignment: within ±1 mm of the centre of the actuator entry slot.

Outside these tolerances you get intermittent contacts, safety relays that will not reset, and premature wear on the entry slot.

Handle and bolt units: the complete access point

Where the guard is a personnel access door rather than a small cover, an actuator alone is not enough. A handle-and-bolt unit combines the actuator with a mechanical door bolt and an external handle, giving:

  • A proper mechanical latch so the door does not rely on the interlock bolt to hold it shut
  • A grab handle for the operator
  • A rear manual lever so a person inside the enclosure can release the bolt and get out
  • An escape-safe access point on fences and large guard doors

Typical options run from compact zinc-alloy bolt units with a short or long ball lever, up to aluminium-alloy door-bolt assemblies with a grab handle, rear manual lever and around 48 mm of bolt travel, plus angled-mount versions with a safety bolt limit screw.

Door gap spacing of 1–10 mm and left- or right-hand installation are normally supported.

Spare actuators are a safety liability

This is the part most plants get wrong. A loose spare coded actuator is a ready-made defeat tool — insert it into the switch head, and the machine believes the guard is closed.

IS 16812 / EN ISO 14119 explicitly requires that defeat be prevented in a reasonably foreseeable manner. That means:

  • Spare actuators kept in secure, controlled storage, issued against a record
  • Actuators fixed with tamper-resistant fasteners or welded, never plain hex bolts
  • Switch mounted so the entry slot cannot be reached when the door is open
  • Periodic inspection for missing or loosened actuators

Ordering checklist

Before you raise the PO, confirm:

  • Door type: sliding, hinged, removable
  • Approach direction relative to the switch head
  • Hinge radius (if hinged)
  • Vibration and impact level → cushioned or rigid
  • Door gap at the leading edge
  • Left or right hand installation
  • Handle-and-bolt unit required? (personnel access doors: yes)
  • Rear unlocking kit required? (walk-in enclosures: yes)
  • Quantity — one actuator per door, plus controlled spares

Full actuator range from Voxintech

The Voxintech VXT-SS series offers eleven interchangeable actuator keys — T-shaped and L-shaped in standard and long lengths, each available cushioned, plus horizontally adjustable, horizontal/vertical adjustable and multi-axis rotating-head versions. Keys are common across the VXT-SS-W2 and VXT-SS-W5 switch bodies, so you can standardise your actuator stock across both formats.

Five handle-and-bolt units and a rear unlocking kit complete the range.

  • VXT-SS-W2-D-NCNO-L-NCNO — slim tall body switch
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — compact body switch

Ask us to select the right actuator for your door →

Frequently asked questions

Is the actuator included with the safety switch?

Usually not. The switch is supplied as a body only and the actuator is ordered separately to suit your door.

Can I use any actuator with any switch?

Only actuators designed for that switch series. Using an improvised or non-matching actuator defeats the coding and voids the safety function.

What is a cushioned actuator for?

It carries rubber bushes that absorb door impact and vibration, extending the life of both the actuator and the switch head on slammed or vibrating doors.

What hinge radius do I need for a hinged door?

Generally greater than 300 mm. Tighter arcs need an adjustable or multi-axis actuator, or the switch moved further from the hinge.

Do I need a handle-and-bolt unit?

For personnel access doors and fence gates, yes — it provides the mechanical latch and the internal release that lets someone get out.


by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

Interlock Defeat: Why Safety Guards Get Bypassed, and How to Stop It

Interlock Defeat: Why Safety Guards Get Bypassed, and How to Stop It

Walk any Indian shop floor and you will eventually find it: a spare actuator key cable-tied into a switch head, a magnet taped to a sensor, a guard door propped open with a spanner in the slot. The interlock is installed, the certificate is in the file, and the machine is running with the guard defeated.

Interlock defeat is not an exotic failure mode. It is one of the most common contributors to serious machine injuries worldwide, and IS 16812 / EN ISO 14119 devotes a whole clause and annex to preventing it. For device selection, see our complete buyer’s guide to guard locking safety interlock switches.

Why people defeat interlocks

Defeat is almost never malice. It is a rational response to a badly designed system:

  • The unlock sequence is too slow. A fifteen-second run-down wait, forty times a shift, is two hours a week of standing still. On piece rate, that is money.
  • The interlock nuisance-trips. A misaligned actuator that drops the relay mid-cycle teaches operators the device is unreliable.
  • Setting and cleaning need access. If the only way to thread material, clear a jam or set tooling is to open the guard, and there is no safe mode for it, the guard will be bypassed.
  • Maintenance needs the machine running. No inching mode, no enabling device — so the guard comes off.
  • A spare actuator is lying around. Opportunity plus friction equals defeat.

The design lesson: if the safe way of working is harder than the unsafe way, the unsafe way wins. Every defeat you find on the floor is telling you something about the machine, not just the operator.

What the standard requires

IS 16812 / EN ISO 14119 requires that interlocking devices be designed, selected and installed so they cannot be defeated in a reasonably foreseeable manner. That last phrase is deliberately broad: the test is not “could a determined saboteur do it” but “would a normal operator under normal production pressure find it easy”.

The standard grades actuator coding as low, medium or high level. A standard mechanical tongue actuator is low-level coded. The lower the coding level, the more supplementary measures the standard expects you to apply.

Ten measures that actually work

Device selection

  1. Use coded actuators (Type 2 or Type 4). A cam or plunger switch (Type 1) can be operated with any flat object. A coded tongue needs the real key.
  2. Choose a device that stays locked without power. Spring locking with solenoid unlocking removes the “just kill the supply and open it” route.
  3. Insist on forced disengagement. ≥80 N / ≥10 mm on the NC contacts, so a welded contact is torn open.

Mounting

  1. Mount out of reach or out of sight. If the operator cannot see or reach the head from outside, the actuator slot is far less inviting.
  2. Shield the entry slot. A simple bracket or shroud that blocks tool access when the door is open costs almost nothing.
  3. Fix the actuator so it cannot be removed — tamper-resistant fasteners, one-way screws or welding. Never plain hex bolts, which vibration loosens and any spanner removes.
  4. Never use the switch or actuator as a door stop. It loosens fixings, creates misalignment, causes nuisance trips — and misaligned interlocks are the ones that get bypassed.

Control and process

  1. Control spare actuators. Secure storage, issue against record, periodic audit. A loose spare is a defeat device.
  2. Monitor plausibility in the control system. Cross-check door and lock signals. Flag combinations that cannot occur — actuator inserted while the door position sensor says open, or bolt extended with no actuator present — and raise an alarm rather than silently continuing.
  3. Log unlock frequency. A guard opened three hundred times a shift is telling you the process needs an access route it does not have.

And the one that matters most

Fix the reason. Provide a setting mode with reduced speed and an enabling device. Shorten the run-down with a proper brake. Add a material feed hatch so the main guard need not open. Design out the friction, and the defeat pressure disappears.

The inspection routine

Add these to the machine’s preventive maintenance schedule:

  • Actuator present, undamaged, and securely fixed
  • No foreign objects in or near the entry slot; no tape, cable ties or magnets
  • Entry gap within tolerance (typically 1.0–3.5 mm) and alignment within ±1 mm
  • Emergency unlocking knob reset to its normal position — an unreset knob prevents the bolt engaging and leaves the guard permanently unsecured
  • Function test: confirm the machine cannot start with the guard open, and stops if the guard is opened
  • Spare actuator inventory reconciled

Devices designed against defeat

The Voxintech VXT-SS series uses a separate coded tongue actuator trapped inside a rotatable metal head, with a spring-loaded lock bolt holding up to 1300 N and forced-disengagement NC contacts. Because the device is spring-locked and solenoid-released, the guard stays locked when de-energised, so cutting the supply does not open it.

  • VXT-SS-W2-D-NCNO-L-NCNO — slim tall body, 4 contacts, independent door and lock monitoring
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — compact body, 6 contacts, dual series safety channels for plausibility-friendly wiring

Request the full range and certificates →

Frequently asked questions

What counts as interlock defeat?

Any action that makes the control system believe the guard is closed when it is not — a spare actuator inserted, a magnet taped to a sensor, contacts bridged in the panel, or a device removed and left operating on the bench.

How does ISO 14119 prevent defeat?

Through coded actuators, mounting requirements, control of spare actuators, and a requirement that the designer consider reasonably foreseeable defeat during selection and installation.

Are coded tongue actuators tamper-proof?

They are defeat-resistant, not defeat-proof. The coding stops improvised tools; controlling spare actuators and mounting the device out of reach handles the rest.

Should I use RFID interlocks instead?

High-level coded RFID devices (Type 4) offer stronger defeat resistance and are worth considering on high-risk applications. Mechanical guard locking is still required where a door must be physically held shut during run-down — the two are often used together.

Who is responsible if an interlock is defeated?

The employer, in practice — but a machine builder who supplied an easily defeated design carries exposure too. Both are best served by designing the incentive to defeat out of the process.


by Voxintech-admin@2022 Voxintech-admin@2022 No Comments

Slim Body or Compact Block? Choosing Contact Configuration and Format for Guard Locking Switches

Slim Body or Compact Block? Choosing Contact Configuration and Format for Guard Locking Switches

Two questions decide which guard locking interlock lands on your bill of materials, and they are usually asked in the wrong order.

Most buyers start with contacts and discover at installation that the switch does not fit the frame. Start with the frame, then work out the contacts — and check both before the PO goes out. For the full selection process, see our complete buyer’s guide to guard locking safety interlock switches.

Question 1: Will it physically fit?

Guard locking interlocks come in two dominant formats.

Slim tall body (approx. 39 × 39 × 183 mm)

Long and narrow, with mounting holes in two pairs down the length.

Use it when:

  • Mounting on a fence post or square-section frame member
  • You have vertical run but very little width
  • You need cable entries on multiple faces — three M20 entries (left, right and bottom) let you route cables however the frame demands
  • The safety design needs door and lock circuits kept independent

Watch out for: the length. On shallow guard frames and short sliding door stiles there is simply nowhere to put 183 mm of switch body.

Compact block (approx. 108 × 89 × 36 mm)

Roughly square and shallow, mounted on four screws.

Use it when:

  • The frame is shallow and the slim body will not fit
  • You are working on a sliding door with a short leading edge
  • Body length is restricted but you have surface area
  • You want more contacts in a smaller footprint

Watch out for: typically a single M20 entry at the base, so cable routing is fixed. Plan the gland direction at design stage.

Measure the frame member — width, depth and available run — before selecting. This one check prevents most of the “it arrived and it doesn’t fit” problems in this product category.

Question 2: How many contacts, and how are they linked?

This is where the safety architecture is decided.

Four contacts: 1NC + 1NO door, 1NC + 1NO lock

The volume configuration. You get:

  • One NC safety contact following the actuator (door closed)
  • One NC safety contact following the lock bolt (bolt extended)
  • Two NO contacts for PLC status — “guard open” and “unlock confirmed”

Wire the two NC contacts in series into a safety relay and the machine can only run when the guard is both closed and locked. That is single-channel safety with full status feedback — correct and sufficient for a great many machines.

Because the door and lock circuits are independent, you can also evaluate them separately where the safety design requires the control system to distinguish “closed” from “locked” on separate channels.

Six contacts: 2NC + 1NO door, 2NC + 1NO lock

Three contacts per block. The critical detail is how the manufacturer links them.

On devices where the blocks are cross-linked internally — typically terminal 12 to 41 and 22 to 51 — each pair forms one complete series “door closed and locked” NC channel. You end up with two such channels available at, for example, terminals 11-42 and 21-52.

Feed those into a dual-channel safety relay with cross-fault detection and you have Category 3 / 4 architecture from a single device, plus two independent NO contacts still free for PLC status.

The trade-off: because the cross-links are made inside the switch, the door and lock functions can no longer be evaluated as separate safety channels. If your design needs independent door and lock circuits, use the four-contact independent format instead.

Side-by-side

Slim tall body, 4 contacts Compact block, 6 contacts
Typical size 39 × 39 × 183 mm 108 × 89 × 36 mm
Contacts 1NC+1NO door, 1NC+1NO lock 2NC+1NO door, 2NC+1NO lock
Safety channels Two, independent Two, series-linked internally
Suits Category 3 from one device Only if the design accepts separate door/lock channels Yes — two full “closed and locked” channels
Cable entries 3 × M20 (left, right, bottom) 1 × M20 (bottom)
Best for Fence posts, frames, separate door and lock circuits Shallow frames, sliding doors, restricted body length

The contact code, decoded

Model numbers in this category follow a consistent logic once you know it:

  • NC = normally closed, NO = normally open
  • A digit prefix gives the quantity: 3NC is three normally closed, 2NC1NO is two normally closed plus one normally open
  • D- denotes the door (actuator) monitoring block
  • L- denotes the lock (bolt) monitoring block

So D-2NC1NO-L-2NC1NO reads as: two NC plus one NO on the door block, two NC plus one NO on the lock block — six contacts in total.

Some series offer a wide catalogue of combinations — door-priority variants with three NC on the door block for separate isolation circuits, lock-priority variants with multiple channels following the bolt, and configurations weighted towards auxiliary status outputs. If your standard configuration is not on the shelf, ask: the variant probably exists.

Both formats in stock

The Voxintech VXT-SS series covers both:

  • VXT-SS-W2-D-NCNO-L-NCNO — slim tall body, 39 × 39.4 × 183 mm, 4 contacts, three M20 entries, independent door and lock circuits. Fourteen contact combinations available across the series.
  • VXT-SS-W5-D-2NC1NO-L-2NC1NO — compact block, 108 × 89 × 35.5 mm, 6 contacts, internally cross-linked to give two complete series safety channels at 11-42 and 21-52.

Both share 1300 N locking force, 24 V DC solenoid, IP67, metal rotatable head, forced-disengagement contacts and the same eleven interchangeable actuator keys — so you can mix formats across a machine without doubling your actuator stock.

Ask us which configuration suits your circuit →

Frequently asked questions

How many contacts do I need on a guard locking switch?

Four is enough for single-channel safety with PLC status. Choose six where you need two complete dual-channel safety inputs from one device.

Can one interlock give me Category 3?

It can support Category 3 if it provides two independent NC safety channels into a dual-channel safety relay with cross-fault detection. The category is a property of the whole circuit, not the switch alone.

What does 2NC1NO mean?

Two normally closed contacts plus one normally open contact on that block.

Which body format should I choose?

Measure the frame first. Slim tall bodies suit fence posts and frame members; compact blocks suit shallow frames and sliding doors where there is no room for a long body.

Can I use NO contacts in the safety circuit?

No. NO contacts are auxiliary signalling only and are not forced-disengagement type. They go to the PLC, never into the safety chain.