The first priority to protect ourselves from the dangers of working on electrical equipment is to eliminate the hazard before engaging in the work. NFPA and OSHA agree. Eliminating the hazard means that all electrical conductors and circuit parts are placed in a de-energized state. Many workers mistakenly believe this means to apply only lockout - tagout (LOTO) procedures. Nothing could be further from the truth. LOTO is only one step in an 8-step process that ensures the equipment is truly de-energized.
Lockout-Tagout is effective, but when used alone, it only proves that a lock and tag has been place on a piece of equipment that is turned off. It does not prove that the equipment is truly de-energized. Several additional factors should be considered:
LOTO alone does not answer these questions. To ensure de-energization, the worker must take the 8 Steps to Establishing an Electrically Safe Work Condition (ESWC) as outlined in NFPA 70E 120.5. Let’s take a look at each step:
Determine all possible sources of electrical energy to the circuit. Many circuits are fed by more than one source. Electrical drawings, labeling, and experienced plant personnel can often guide the worker to discover all sources of energy. If more than one source of energy exists, both sources need to be shut off.
The 3 ATS units above have more than one possible source of power (normal power and emergency generator power.)
Open the disconnect device for each source. This is straight forward. The worker is turning off power from all sources of possible energy to the equipment being serviced.
If possible, visually verify that the disconnecting means are open and disengaged. Many devices have a viewing window in which the worker can see whether the blades have physically disconnected from the line side because electrical devices occasionally malfunction and fail to open on each phase.
Release stored electrical energy. Devices such as batteries, capacitors, and inductors may store energy even after power to the equipment has been shut off. Energy dissipation can take several minutes depending on the type of device. Make sure that you are aware of any such devices associated with the equipment being worked on.
Label from a VFD outlining the steps to dissipate stored energy.
Block or release stored non-electrical energy so that the electrical equipment cannot be energized. Mechanical devices, such as springs, must be blocked.
Apply LOTO procedures in accordance with the company safety program. The LOTO program is the foundation of the ESWC process and the only step that ensures the circuit cannot be accidently turned back on. The LOTO procedure has several steps of its own to ensure the safety of the worker. The main goal is to prevent unintentional energization by other personnel while the worker is actively engaged with the equipment.
A proper LOTO process ensures that the circuit cannot be turned on by someone not involved in the process.
Test for the absence of voltage. Commonly known as test-before-touch, this procedure involves a real voltage tester, not a proximity tester. The voltage should show “000” volts and should be applied to both phase-to-phase and phase-to-ground electrical conductors. Take note that this is a 3-step process:
• Check with a known source like a receptacle to ensure that the meter is working.
• Verify the absence of voltage in the equipment being worked on.
• Check the voltage again with the same known source as before.
If the voltage shows anything other than zero volts, the equipment is not de-energized. Use a properly rated voltmeter, not a proximity tester!
If there is a possibility of induced voltages or stored electrical energy in the circuit, ground all circuit conductors before engaging in the work.
If necessary, grounding all circuit conductors ensures that overcurrent protective devices operate if a circuit is accidentally energized due to equipment failure or static buildup.
There you have it. This 8-step process addresses all the concerns and proves that the circuit being worked on is de-energized. These steps address the possibility of inaccurate drawings or labeling and the possibility of having more than one power source. These steps check that the circuit parts disengaged when the switch was turned to the off position and verify for the worker that voltage is not present.
If you’ve been relying solely on LOTO to eliminate electrical hazards, consider adopting the entire process of establishing an ESWC as outlined in NFPA 120.5 and OSHA 29 CFR 1910.333. Remember that these 8 steps can save your life.