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.

Part of our guard locking series: the complete buyer's guide  •  spring lock vs solenoid lock.

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The standards map

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 MTTF_D.

• 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.

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