Generator yard and paralleling gear.
The generator yard is the one part of the plant that is deliberately exercised under load every month — which means the 'first operation after maintenance' row of the likelihood table is not an edge case here. It is the schedule.
Paralleling switchgear is switchgear
Under the table method, 600 V-class switchgear is Category 4 with a 20 ft arc flash boundary — parameters 35 kA, up to 0.5 s clearing, 455 mm working distance. Paralleling gear earns the class honestly: multiple sources capable of feeding a fault, generous clearing times during paralleling windows, and control complexity that invites abnormal states.
Table 130.5(C)(3) draws the operational line: operating a breaker under normal operating conditions is a No for arc flash likelihood — but the first operation after the equipment has been serviced or maintained is a Yes. A generator plant on a monthly PM cycle produces 'first operations' twelve times a year per unit. The likelihood table was written for exactly this, and a plant that treats the post-PM test start as routine has misread it.
Every generator is a source; so is the utility
Lockout in this yard is a sources problem before it is a procedure problem. A paralleling bus can be fed by any generator on the bus, by the utility through the transfer scheme, and by control power that rides through from more than one origin. Article 120 requires disconnecting all sources and verifying absence of voltage at the point of work — and 'all' is a longer list here than anywhere else on site except the battery room.
Exception No. 2 to 110.2(B) is the provision that makes the yard workable: an energized disconnecting means may be operated to achieve an electrically safe work condition or to return equipment to service, provided a risk assessment finds no unacceptable risk. Opening the paralleling breaker, racking it, pulling control fuses — that sequence is the exception working as designed. It is not a licence for anything beyond the switching itself.
Load bank testing is energized interaction
A load bank run feels like a test because nothing is being repaired. But connecting load bank cables to an energized bus, or landing them ahead of the test, is work on or near exposed parts, and the walk applies in full: trigger, justification, package, permit gate. Connecting to a de-energized, locked-out bus and then energizing for the run is the sequence that keeps the whole evolution on the right side of 110.2(B). The test itself — readings, adjustments, observation with doors closed and secured on healthy gear — is normal operation.
Generator control cabinets with the covers off during a test run, 'because we need to watch the governor.' Control circuits at or below 125 V have a No likelihood row — but that row requires no other exposed equipment above 125 V in the space, and an open paralleling section a meter away voids it. The watching is fine; the open covers next to it are the finding.
Post-maintenance test start? That is the abnormal-operation row, not the normal one. Walk it before the first start, not after.
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.