I’m hoping to learn if there are any rules-of-thumb regarding a permanently-installed breaker panel and the quantity and capacity of the breakers located within it. The space in question is a soundstage for single-camera film/video shoots (within a commercial office building), which under normal circumstances would only have a company switch—the production gaffer would use portable distribution boxes to break out power feeds as needed. In this example however, the space has a breaker panel feeding permanent wall-mounted 120v receptacles (100A, 60A, 20A) instead of a company switch. This is a simple breaker panel: no dimming or remote/relay control pertains.
I recently saw an installation where a 225-amp 3-phase 120/208 panel had the following collection of single-pole breakers (each feeding individual 120v wall receptacles: Edison and Stage Pin (Bates) respectively):
(18) 20A breakers
(16) 60A breakers
(4) 100A breakers
…that adds up to 1720 amps if every receptacle were to be fully loaded. Divided by 3, that’s 573.3 amps per leg in a box with a 225-amp main, presuming the internal bussing of the panel roughly divides the circuit loads among the legs.
I understand the concept of diversity, and the presumption that everything won’t be loaded simultaneously, but I hope to better understand the design thinking here. I know the main breaker protects the feed wiring, and the branch circuit breakers protect the branch wiring to the receptacles. In a motion picture studio environment, there is no way to calculate the “actual” load demand, since all of the load circuits are receptacles and it’s a guess to anticipate how much power will be used. I believe certain residential and commercial demand calculations are done by the square foot, but again that’s not really this application. Are there any restrictions (other than how many breakers will fit) that apply to the number or size of breakers in a panel? How would a theatre consultant or engineer estimate these loads and the number/capacity of circuits?
It’s extremely convenient to have so many circuits and so many receptacles, but is this design responsible? And would this room within the office building fall within NEC 520 or 530? To clarify, there is no live audience in this space.
Thanks.
I recently saw an installation where a 225-amp 3-phase 120/208 panel had the following collection of single-pole breakers (each feeding individual 120v wall receptacles: Edison and Stage Pin (Bates) respectively):
(18) 20A breakers
(16) 60A breakers
(4) 100A breakers
…that adds up to 1720 amps if every receptacle were to be fully loaded. Divided by 3, that’s 573.3 amps per leg in a box with a 225-amp main, presuming the internal bussing of the panel roughly divides the circuit loads among the legs.
I understand the concept of diversity, and the presumption that everything won’t be loaded simultaneously, but I hope to better understand the design thinking here. I know the main breaker protects the feed wiring, and the branch circuit breakers protect the branch wiring to the receptacles. In a motion picture studio environment, there is no way to calculate the “actual” load demand, since all of the load circuits are receptacles and it’s a guess to anticipate how much power will be used. I believe certain residential and commercial demand calculations are done by the square foot, but again that’s not really this application. Are there any restrictions (other than how many breakers will fit) that apply to the number or size of breakers in a panel? How would a theatre consultant or engineer estimate these loads and the number/capacity of circuits?
It’s extremely convenient to have so many circuits and so many receptacles, but is this design responsible? And would this room within the office building fall within NEC 520 or 530? To clarify, there is no live audience in this space.
Thanks.