Safety

The steps that keep you alive: de-energize, lock it, prove it dead. This is a refresher, not training. Follow your employer's written program and NFPA 70E.

Lockout/tagout: the electrically safe work condition

Find every source of supply, from up-to-date drawings, labels and a walk-down. Watch for backfeeds: generators, PV, UPS, control power from another panel, capacitors.
Shut off the load, then open the disconnecting device for each source.
Where you can, look at the blades or the racked-out breaker to see it's open.
Put your own lock and tag on each disconnect. Only you remove your lock.
Test each phase conductor or circuit part, phase to phase and phase to ground, with a properly rated tester, checking the tester on a known source before and after.
Where there could be induced voltage or stored energy, ground the conductors with rated temporary grounds before touching them.

Until the test is done, treat it as energized and wear the PPE for live work.

Live-dead-live

Live: check your meter on a known live source (or a proving unit) on the voltage range you'll use.
Dead: test the de-energized circuit: every phase to every phase, and each phase to ground.
Live: check the meter again on the known source. If it failed between steps, your "dead" reading means nothing.

Use a meter rated for the location: CAT III for panels and feeders, CAT IV at the service and outdoors at the utility side, at the system voltage or higher.
Inspect leads for cracks and exposed metal. Use shrouded probes; keep fingers behind the guards.
Non-contact testers are for a quick look, not for proving dead.

Shock approach boundaries (AC, 50 to 750 V)

Voltage, phase to phase	Limited: movable conductor	Limited: fixed part	Restricted
50 to 150 V	10 ft 0 in	3 ft 6 in	Avoid contact
151 to 750 V	10 ft 0 in	3 ft 6 in	1 ft 0 in

Limited approach boundary: unqualified people stay outside unless a qualified person escorts them.
Restricted approach boundary: only qualified people, with shock protection (rubber gloves, insulated tools) and a plan.
The arc flash boundary is separate and is often farther out. It's on the equipment label.

Arc flash basics

An arc flash can reach thousands of degrees in a fraction of a second. Most happen when someone is working on or near energized parts: dropping a tool, a test probe slipping, racking a breaker.
Incident energy is measured in cal/cm². The arc flash boundary is where it falls to 1.2 cal/cm², about the onset of a second-degree burn on bare skin.
Read the equipment's arc flash label: it gives the incident energy or PPE category, the boundary and the shock data.
Your PPE has to be rated at or above the incident energy. Wear arc-rated clothing as the outer layer, with no meltable fabrics underneath.

PPE categories

Category	Minimum arc rating	Typical gear
1	4 cal/cm²	Arc-rated shirt and pants or coverall, face shield or arc flash suit hood, hard hat, safety glasses, hearing protection, leather gloves or rubber gloves with protectors
2	8 cal/cm²	As category 1, with an arc-rated balaclava under the face shield (or a hood), and leather work shoes
3	25 cal/cm²	Arc flash suit: jacket, pants, hood and gloves
4	40 cal/cm²	Heavier arc flash suit, same pieces

Rubber insulating gloves

Class	Max use voltage (AC)
00	500 V
0	1,000 V
1	7,500 V
2	17,000 V
3	26,500 V
4	36,000 V

Air-test gloves for leaks before every use, and wear leather protectors over them.
Gloves need an electrical retest at least every 6 months once issued. Check the stamped date.

NFPA 70E (Article 120, 130.4, Table 130.5(G), Table 130.7(C)(15)(c)); OSHA 1910.147, 1910.333, 1926.417