Generator cables run into an open 600-volt switchboard: what OSHA and the NEC require

According to the post, the city had not yet hooked up the transformer, so the general contractor brought in a large generator. Its cables were fed into the bottom of the main switchboard, which cannot be closed with them in place, leaving live bus open in a cramped electrical room that plumbers and other subs walk through. Some colleagues think he is overreacting, he wrote.

The federal rules do not back that view. Under 29 CFR 1926.403(i)(2), live parts at 50 volts or more must be guarded by an enclosure or by location: a room only qualified persons can enter, partitions, a raised platform or at least 8 feet of elevation. Entrances to such rooms need signs barring unqualified people. Section 1926.405(b)(1) says openings where conductors enter a cabinet must be effectively closed. Section 1926.416(a)(1) bars employers from letting anyone work close enough to touch a live circuit unless it is de-energized and grounded or effectively guarded, and 1926.416(b)(1) requires barriers so electrical workspace is not used as a passageway while energized parts are exposed.

The National Electrical Code says much the same in Section 110.27. Live parts from 50 to 1,000 volts must be in approved enclosures, in a room locked to all but qualified people, behind substantial partitions, or, for 301 to 600 volts, at least 8 feet 6 inches above the floor. Entrances need permanent warning signs that are not handwritten, according to a code column by Charles R. Miller in Electrical Contractor magazine.

In practice, an open board can stay energized only if the room is locked to everyone but qualified electricians, posted, and kept free of other trades. A room plumbers use every day does not qualify. The options are to land the generator leads so the switchboard covers go back on with the entry openings closed, or to lock the room until the permanent service is live. Clearance still counts: for 151 to 600 volts to ground, OSHA Table K-1 calls for 3 to 4 feet of clear working space in front of exposed live parts, depending on what is opposite.