Main switchgear rooms.
Almost every energized-work decision in the building either starts or ends in this room. It is also home to the most-misquoted number in the trade: the '10-foot rule' that is actually the boundary for an exposed movable conductor — not for the fixed bus in front of you.
The boundary numbers, stated correctly
For 480 V fixed circuit parts — bus, lugs, breaker stabs, everything bolted into this room — the limited approach boundary is 3 ft 6 in. and the restricted approach boundary is 1 ft 0 in. The 10 ft 0 in. figure that circulates in the field is the limited approach boundary for an exposed movable conductor, a different column of Table 130.4(E)(a) entirely. Teaching the 10-foot number for fixed parts inverts the table.
These are shock boundaries, and they exist only where parts are exposed. The arc flash boundary is a separate, independent distance — under the table method for 600 V-class switchgear it is 20 ft, which is usually the largest boundary in the room and the one that governs where the second person stands.
What the table method really says about this room
600 V-class switchgear carries Category 4 under Table 130.7(C)(15)(a), with parameters of 35 kA and 0.5 s clearing at 455 mm. Main gear close to the service transformer can exceed the fault-current parameter, and older air-frame mains with intentional short-time delay can exceed the clearing-time parameter — and either exit forces an incident energy analysis under 130.5(G). The rooms most likely to breach the parameters are precisely the main rooms. If there is one place the facility should refuse to run on table values, it is here.
Arc-resistant switchgear earns its N/A in both tables — likelihood and PPE — only with doors closed and secured and the event within its rating. Open a low-voltage compartment door, defeat a latch, or rack with covers off, and the rating is out of the picture; the gear is ordinary switchgear again. The rating protects operation, not maintenance.
The permit gate lives at the restricted boundary
130.3(A) requires an energized electrical work permit for work within the restricted approach boundary — 1 ft 0 in. here — or for the closed-door interaction case. But 130.3(C) exempts testing, troubleshooting and voltage measuring by qualified persons using Chapter 1 practices and PPE, along with thermography and visual inspection that stay outside the RAB. Which means the two most common energized tasks in this room — verifying absence of voltage and shooting IR — are justified-energized, PPE-required, and permit-exempt. Knowing where the paperwork is and is not required is half the battle of getting crews to respect it where it is.
An immaculate switchgear room with the incident-energy labels facing a housekeeping pad nobody can stand on, and a 20 ft arc flash boundary that ends inside the adjacent, fully occupied electrical room next door. The boundary does not stop at drywall. Chalk it on the floor once and the conversation changes permanently.
Door open on energized gear? You are at the trigger question already. Run the walk before the screwdriver comes out.
This is the material of the 8- and 16-hour NFPA 70E classes — taught on the 2027 edition, against data center topology, about 55 times a year. Private onsite days run against your one-lines.