[SML] Computing a lighting load

[PATRICK MCCREARY]

I have always used a 50% assumption. Then divide by 3, assuming you're 
using a 3-phase 5-wire feeder. Then assume you want a somewhat standard 
size - in your case, 600A 3-phase. We have a 300A 3-phase for 176 2.4K 
dimmers, and have never even come close. I'm not sure I would have room 
to hang enough fixtures to load the system fully.

Patrick

On 2/11/2015 12:06 PM, Dougherty, Jim via Stagecraft wrote:
> When looking at a lighting system (particularly in the context of a 
> new or replacement installation), is there a formula used to calculate 
> a systems lighting load?  For example, assume an installation has 200 
> 2.4K dimmers. To size the service at 4000A to handle the load if the 
> system were to be run entirely at full is ridiculous.  How is it, 
> then, designed/specified?  Based on a percentage of that maximum? 
>  Taking into account a typical or perhaps maximum instrument count 
> from past shows, and applying a formula to that number based on the 
> assumption that no plot’s lights are all on at once?  Darts and a 
> Square D catalog?
>
> Ideally I’m looking for a reference based on manufacturer’s 
> requirements, NEC, industry standard, etc.  Rule of thumb is 
> definitely welcome but not as helpful in this context.  I find it 
> interesting that the load will presumably be diminishing over time as 
> our industry gradually shifts to a greater reliance on LED and other 
> lower-load fixtures.  Our own system will be a mix of conventional and 
> LED for a long time to come.
>
> Thanks.
>
> - Jim Dougherty
> ATD, Middlebury College Theatre Dept.
>
>
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-- 
G. Patrick McCreary
Technical Director
Department of Theater and Dance
Indiana University of Pennsylvania

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