Commercial basics: three-phase systems, motor circuits, panel schedules, tenant-improvement lighting retrofits, and the labels commercial work requires
In one paragraph
The first commercial call is usually small (a tenant improvement, a motor that will not start, a lighting retrofit) and it is a different world in four ways: the power is three-phase, so voltages, neutrals and the high-leg marking are new; motor circuits are sized from the code's tables and three separate rules, not from the nameplate alone; every panel needs a legible schedule and, on commercial gear, an arc-flash warning label; and the lighting is governed by the nonresidential half of the Energy Code, which puts a certified acceptance test technician between you and the final. The contract changes too: the residential home-improvement rules of Phase 3 do not apply, and the 10-point CSLB notice of B&P 7030(a) goes on every prime contract. This lesson is the vocabulary and the section numbers for the first year of commercial work.
The rule
Motor branch-circuit conductors are sized at not less than 125 percent of the motor's full-load current from Tables 430.248 and 430.250 (2025 CEC 430.22); running overload protection is set by 430.32 (115 or 125 percent of nameplate for continuous-duty motors); and the branch-circuit short-circuit and ground-fault device is sized from Table 430.52 (250 percent of full-load current for an inverse-time breaker, with the next-size-up allowances). Non-dwelling switchboards, panelboards and similar equipment likely to be worked on energized carry an arc-flash warning (110.16); a three-phase system with a high leg is marked (110.15); panel circuits are legibly identified (408.4); and reconditioned panelboards may not be installed in California (408.2(A)). Nonresidential lighting controls require acceptance testing by a certified technician under the Energy Code.
Why it matters
Commercial work pays better per hour and fails in different places: a motor breaker sized like a residential circuit trips on every start, a missing arc-flash label or panel schedule fails a final, and a lighting retrofit without acceptance testing never closes its permit. Learning the three-phase vocabulary and the motor tables once turns the property manager's small tenant-improvement call into the account that carries the winter.