[SML] Computing a lighting load

[Lou Poppler]

On 2/11/15, PATRICK MCCREARY via Stagecraft <stagecraft at theatrical.net> wrote:
> 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.

A quick back-of-the-envelope sanity check says your system trips when
any phase exceeds 36KW.  If your users are always careful to balance
the load over all 3 phases, then you are good up to 108KW.  But if
some show winds up with 37 1Kpars accidentally all on the same phase,
and all at full at the same time, then not so good.  Many modern
electric rooms would use a common-trip 3ø breaker, so you might expect
to lose all dimmer power when one phase is overloaded.