Control/Dimming Understanding NEC / Panelboard Breaker Capacities & Quantities for a Sound Stage

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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.
 

BillConnerFASTC

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Its all based on load schedules. Ive been assigning laodes to circuits on panel schedules gor a long time. In the tunsten halogen world and dimmees, it has varied but mmost recently 1150 (2x575) for every production circuit. With 200 or so, new i was way safe. In an LED world, i use 1200 watts per 20 amp cirvuit. Again several hundred units - way more than they'll ever have, let alone all on at full. Fixed loads are just that.

Circuit breakers and dimmers are not loads. Figure out how many lights of what wsttage you might possibly ever have connected. All receptacles will never be fully load. That 225 amp panel will handle 140 - 575s, or 600+ LEDs. How big is the room and how many fixtures can they feasibily hang and focus?
 
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danTt

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Its all based on load schedules. Ive been assigning laodes to circuits on panel schedules gor a long time. In the tunsten halogen world and dimmees, it has varied but mmost recently 1150 (2x575) for every production circuit. With 200 or so, new i was way safe. In an LED world, i use 1200 watts per 20 amp cirvuit. Again several hundred units - way more than they'll ever have, let alone all on at full. Fixed loads are just that.

Circuit breakers and dimmers are not loads. Figure out how many lights of what wsttage you might possibly ever have connected. All receptacles will never be fully load. That 225 amp panel will handle 140 - 575s, or 600+ LEDs. How big is the room and how many fixtures can they feasibily hang and focus?
Or 16 5k Fresnels, which would be a lot for a single cam studio, but also not terribly outside the realm of film..
 

RonHebbard

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Or 16 5k Fresnels, which would be a lot for a single cam studio, but also not terribly outside the realm of film..
@danTt Wouldn't 16 Five Kw. Fresnels put you past 80% on your 225 Amp panel and are you allowing for in-rush when cold? Are we to assume a 3 phase 5 wire panel? With five 5K's per phase, how are you powering that last 5K?
Toodleoo!
Ron Hebbard
 
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danTt

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@danTt Wouldn't 16 Five Kw. Fresnels put you past 80% on your 225 Amp panel and are you allowing for in-rush when cold? Are we to assume a 3 phase 5 wire panel? With five 5K's per phase, how are you powering that last 5K?
Toodleoo!
Ron Hebbard
Well, either I'm assuming they have a 140v service, or I'm doing quick bad math :) You're right, it's probably actually 12 5ks. Still a lot of light for a small film studio, but not completely unheard of.
 
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BillConnerFASTC

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Or 16 5k Fresnels, which would be a lot for a single cam studio, but also not terribly outside the realm of film..
In a modern office building where this is likely used for promotional and such, not even sure its taller than one story, in 2018, why would they not be using LED? I suspect tye hvac isnt close to being up to 16 5ks. Maybe it is a 40 x 40 2-3 story sound stage for feature films - but i doubt it.
 

danTt

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NY
In a modern office building where this is likely used for promotional and such, not even sure its taller than one story, in 2018, why would they not be using LED? I suspect tye hvac isnt close to being up to 16 5ks. Maybe it is a 40 x 40 2-3 story sound stage for feature films - but i doubt it.
I did not get the sense from the OP that this was specifically about fitting out a new install, but rather about an venue they were in recently that had this power setup. Depending on the age, I could see tungsten being a much more likely encounter. Still a lot of light for a venue of indeterminite size, but much more feasibly reachable with film fresnels than 140 HPLs.
 
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derekleffew

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—the production gaffer would use portable distribution boxes to break out power feeds as needed.
What would he bring in? Probably not much more than what was necessary. Let's say he was a little paranoid and brought in
(18) 20A breakers
(16) 60A breakers
(4) 100A breakers
Would that be wrong? It all depends on the fixtures/lamps.

It seems to me this doesn't differ much from a derated dimmer rack feed. No one feeds a 96x2.4 dimmer rack with 640a/leg. Or do they? @BillConnerFASTC uses 1150w per dimmer, but does he leave 17% of dimmers unused?

See also the attached article Dimmer Feeds--How Much Is Enuf ?
 

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tjrobb

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Cedar Rapids, Iowa
Afaik, NEC is quiet on studio loads. Normal offices are 3.5W/sf for FEEDERS and minimum 180VA per yoke for receptacles (i.e. a double would be 360).
Again, minimum. In the end, the NEC is a safety code and is more concerned the wire handles the load than what the load is. If you're thinking an outlet is going to be handling 1200W, design for it.
Lastly, there's a "nonconcurrent load" caveat. If, as an example, you have 6 L14-30 but it's infeasible more than 2 ever get used at once those last 4 can have a design load of 0W. (Edit: this is sometimes seen in ballrooms for light shore power loads).
 
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BillConnerFASTC

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Clayton NY 13624
I know one consultant that fed 96*2.4 racks at 800 amps - full load continuous.

I'm not sure what the 17% refers to but high schools with 2 or 3 racks at 800 amps bussed never get near maxing it - even if their initial inventory if 125-150 fixtures doubles. (Or triples - and how many high schools get to 200-300 fixtures really?)

I've also looked at it from how many fixtures fit - 18" on center, every rail, boom, and electric.

And how much time does a theatre have to hang and focus? Another limit.

Frankly determining a realistic load and profile for purposes of designing the AC is trickier than feeders. Having watched an ampmeter on the feed for Yale Rep and knowing it rarely got above 50-60 amps at a time when some T12s were still in use is was informative.

Now, in an all LED world, a couple of 48 circuit relay panels, a 200 amp feed each seems silly large but that's what I usually use.