Lockout-tagout exists to close the gap between believing a circuit is isolated and knowing it is, and the difference between those two states is exactly where fatal electrical incidents happen. An assumed isolation is not an isolation at all until it has been locked, tagged and proven.

Why each step exists

Isolating the supply removes the source of energy. Locking it prevents anyone — including the person who isolated it — from re-energising the circuit while work is in progress, since a lock physically blocks the switch or breaker regardless of who else might operate it without knowing work is underway. Tagging identifies who applied the lock and why, so anyone finding it knows not to remove it. None of the three steps substitutes for the others: a tag without a lock can be ignored, and a lock without a tag leaves the next person unable to tell who to contact before removing it.

Proving dead is a separate, final step

Locking and tagging isolate the supply; they do not by themselves confirm the circuit is actually de-energised, since an isolation point can be wrong, mislabelled, or bypassed by a source no one accounted for, such as backfeed from another supply or stored energy in a capacitor. The circuit must be tested with a voltage detector proven to work immediately before and after the test, confirming the detector itself has not failed silently. Only after this test shows zero voltage should the circuit be treated as dead.

Multiple workers and group locks

Where more than one person is working on the same isolated circuit, each individual should apply their own personal lock, not rely on a single lock applied by whoever isolated the circuit first. A group lockout device or hasp allows multiple personal locks to be applied to a single isolation point, so the circuit cannot be re-energised until every individual has removed their own lock, meaning no one person’s premature departure can put someone else at risk.

Restoring supply at the end of the task

Before removing locks and restoring supply, the work area needs checking to confirm all tools, temporary grounds and personnel are clear, and everyone who applied a personal lock needs to be accounted for before their lock is removed. Restoring supply while any of these checks is incomplete reintroduces exactly the hazard the isolation was put in place to control.

For the testing step itself in detail, see testing for absence of voltage, and for temporary grounding once dead is confirmed, see grounding and earthing for temporary electrical safety.

Frequently asked questions