De-energizing, lockout and test before touch

The single most effective way to prevent electrical injury is to work on equipment only after it has been de-energized, locked out and proven dead. Workplace electrical safety standards call this establishing an electrically safe work condition, and they make it the default: energized work is the exception that must be justified. This lesson explains what the process involves, what unqualified workers' roles are, and why 'test before touch' matters so much. HSE-210 covers lockout in depth for all forms of hazardous energy; this lesson focuses on the electrical side.

Why de-energize?

De-energizing removes the shock and arc flash hazard at its source. Once a circuit is disconnected from every source of supply, locked so that it cannot be re-energized, and tested to confirm there is no voltage, work can proceed without approach boundaries or arc-rated PPE for the shock and arc flash hazards of that circuit. Many incidents happen because someone believed a circuit was off when it was not: the wrong breaker was opened, a second source was missed, a switch failed, or someone switched it back on.

CSA Z462 requires that energized electrical conductors and circuit parts be put into an electrically safe work condition before an employee works within the limited approach boundary or interacts with equipment where an increased likelihood of injury from arc flash exists, unless energized work is justified. Provincial regulations, such as Ontario's industrial and construction regulations and BC's Part 19, require de-energizing and lockout before work on electrical equipment, with limited exceptions for qualified workers following specific procedures. CSA Z460 covers lockout and other methods of hazardous energy control.

Establishing an electrically safe work condition

A qualified person establishes an electrically safe work condition by following a defined sequence. The steps below summarize the process described in the standards.

• Identify all possible sources of electrical supply, using up-to-date drawings, diagrams and identification tags. Equipment may have more than one feed, a backup generator, a UPS, or control power from another panel.
• After properly interrupting the load current, open the disconnecting device for each source.
• Where possible, visually verify that all blades of the disconnect are fully open or that drawout breakers are withdrawn to the fully disconnected position.
• Release stored electrical energy, for example from capacitors, and block or release stored mechanical energy.
• Apply lockout devices according to the documented lockout program, with each worker applying their own lock.
• Using an adequately rated test instrument, test each phase conductor or circuit part to verify that it is de-energized. Test phase to phase and phase to ground. Check the tester on a known live source before and after the test.
• Where conductors could become re-energized or induced voltage could appear, apply temporary protective grounding equipment.

Only qualified persons may perform the testing step. Unqualified workers may be affected employees whose equipment is locked out, or may be authorized for lockout of specific machines under a machine-specific procedure, but they must not test for absence of voltage on electrical conductors or work inside electrical equipment.

Test before touch: the live-dead-live check

A voltage tester is only useful if it works. A tester with a dead battery, a broken lead or the wrong range can show zero volts on a live circuit. The live-dead-live method catches this. First, test the tester on a known live source of similar voltage to prove it works. Second, test the circuit you are about to work on, every phase and between phases and ground. Third, test the tester again on the known live source to prove it did not fail during the test. Only then is the circuit treated as dead.

Test instruments must be rated for the voltage and the measurement category of the location, marked for example CAT III 600 V or CAT IV 600 V, and certified or listed. A non-contact voltage indicator, the pen-style device that beeps near live wires, is useful for a quick check but is not accepted as proof of absence of voltage, because it can miss shielded or DC conductors and can fail silently. Some facilities install permanently mounted absence of voltage testers on equipment, which automate the live-dead-live sequence; they are covered by product standards and can be used as part of the verification where the workplace standard allows.

Stored energy in electrical equipment

Capacitors in variable frequency drives, power supplies, welders, power factor correction banks and large motor circuits can hold a lethal charge after power is removed. Most have bleed resistors that discharge them over a few minutes, but resistors can fail. Equipment labels often state how long to wait before opening, and qualified workers verify discharge with a meter.

When energized work is justified

Working on or near exposed energized parts is allowed only when it can be justified. The standards recognize two main justifications. First, de-energizing would introduce additional or increased hazards, for example shutting down life-support equipment, emergency alarm systems or ventilation in a hazardous location. Second, de-energizing is infeasible because of equipment design or operational limits, for example diagnostic testing and troubleshooting that can only be done with power on. Inconvenience, cost or production schedules are not acceptable reasons.

Where energized work is justified, the standards require an energized electrical work permit for most tasks, signed by management, describing the work, the justification, the shock and arc flash risk assessment, the boundaries, the PPE, the safe work practices, how unqualified persons will be kept out, and the job briefing. Some tasks, such as testing, troubleshooting and voltage measurement by qualified persons, can be done without a permit when the right safe work practices and PPE are used. Unqualified workers are never part of the energized work itself.

The unqualified worker's role in lockout

Unqualified workers are often affected employees: they operate or work near the equipment that is locked out. They must understand the purpose of lockout, recognize locks and tags, never try to start locked-out equipment, and never remove or tamper with someone else's lock or tag. When work is finished, the authorized person restores the equipment and tells affected employees before re-energizing. Where an unqualified worker is authorized under a machine-specific procedure to lock out a machine, for example at its main disconnect, they apply their own lock and verify that the machine will not start using its normal controls, but they do not open electrical enclosures or test conductors.

Job briefings and communication

Before any work on electrical equipment, the qualified person in charge holds a job briefing with everyone involved. It covers the hazards, the procedures, any special precautions, the energy sources and how they will be controlled, the PPE and the emergency plan. Affected employees are told what will be shut down, for how long and how they will know when it is safe to restart. Good briefings prevent the classic failures of lockout: someone switching equipment back on because they did not know work was under way, or a second source being missed because no one checked the drawings. If anything changes during the job, the briefing is repeated.

Unqualified workers can help by asking questions at briefings, by reporting anything unusual they notice about the equipment, and by keeping clear of the work area until they are told it is safe.

Locks and tags also have to be the right ones. Lockout devices should be durable, standardized and identifiable as belonging to a specific person, and tags should state who applied them and why. Electrical lockout often needs special devices: breaker lockouts that clamp onto a handle, plug lockouts that enclose a cord cap, and group lock boxes for jobs with many isolation points.