[SML] L21-30 power supply

[e-mail frank.wood95]

Dan

As we both know, Code requirements are not always sensible. With a
genuine three-phase load, such as a motor, dropping all three phases
at once is desirable. I can't work out what a three-phase motor
deprived of one phase would do, but I am prepared to bet that it would
be very unhappy.

A stage lighting installation is not like that. It is, effectively,
three single-phase installations, spread across the three phases for
balance purposes on the whole site load.

Back in the days of thyratron dimmers, the poor neutral had to carry
the total load current. This was what made them so damned expensive,
as you needed a Star-Delta transformer tto balance up the load.

On 28 February 2015 at 20:49, Dan Sheehan <dsheehan.sml at gmail.com> wrote:
> Frank, Case under discussion concerns a 5-wire, 3-phase *outlet receptacle*.
> I haven't checked the Code, but I strongly suspect that in this situation,
> it would be required that if one phase trips, the whole receptacle and
> anything plugged into it (like extension cord and nobody-knows-what)
> must be depowered.
>
> Note this is different from the case of an independent  120V(in US)
> load connected to one leg,
> which can be protected by one breaker (I think... again, IANAE).
>
> On Sat, Feb 28, 2015 at 2:22 PM, e-mail frank.wood95 via Stagecraft
> <stagecraft at theatrical.net> wrote:
>> Richard.
>>
>> Why do you think this? Dimmer packs are essentially single phase
>> devices, the total load being spread across three phases for reasons
>> of load balancing. If your breakers work on strict trades union
>> principles (One out: all out) tripping one breaker will lose you the
>> whole works, and you've lost the whole show. With two phases left, you
>> can usuallyy cobble up enough lights to keep going.
>
> --
> ...Dan Sheehan
> Fixer of things that break



-- 
Frank Wood