Guards and Interlocks: Commissioning Guide

By Dovydas Kersys · Chapter 29 of 58 in Machine Commissioning.

Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.

Guard switches, interlocks and trapped-key systems should be tested in every relevant machine mode. The machine must respond correctly when a guard is opened, closed, faulted or misaligned.

Why this matters during commissioning

Guard commissioning frequently reveals mechanical alignment issues that software cannot solve.

Commissioning procedure

Check guard alignment and switch actuation distance.
Verify both channels and discrepancy diagnostics where used.
Open the guard during the permitted test condition and confirm hazard removal.
Close the guard and confirm no automatic restart occurs unless specifically designed and risk-assessed.
Test start inhibition with guard open.
Check series-connected devices for diagnostic limitations.

Common failure patterns

Actuator barely reaches the switch and becomes intermittent.
Guard closed indication exists but lock confirmation is ignored.
Guard opening stops only one of several hazards.
Mechanical bypass actuator left in place after test.

Evidence to record

Measured value and test point
Expected value / expected state
Observed value / observed state
Pass/fail result and any deviation
Name/date or responsible person where required

FIELD RULE: Guard switches are mechanical devices as well as electrical safety devices; alignment is part of commissioning.

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