[SML] L21-30 power supply

[e-mail frank.wood95]

Richard

I had forgotten your power distribution systems, which I consider
mildly insane. Most users receive all or part of a three-phase,
four-wire feed, plus an earth wire. While the high voltage
distributions are three-phase delta, only really heavy power users get
anywhere a delta system. Places such as steel mills, for example.

For the rest, I regard your systems  with a delta distribution, with
one side centre-tapped to provide a pseudo-neutral as wholly
insanitary. Westinghouse was right, and Edison wrong.

Yes, with one phase missing,  the neutral current will be higher than
normal. At this time of night, I am not prepared to start the
calculations. But don't forget that the return current from the
missing phase will not be flowing in the neutral.

On 28 February 2015 at 20:21, Richard Niederberg <ladesigners at gmail.com> wrote:
> Dear Frank,
> We do not want an overloaded neutral or weird harmonics to be present
> ANYWHERE in the system. Two out of three legs maxed out can cause problems
> elsewhere in the installation, especially if the Delta-to-Wye transformer
> was being fed by a service with a 'wild' leg.
> /s/ Richard
> _________
>
> On Sat, Feb 28, 2015 at 11:22 AM, e-mail frank.wood95
> <frank.wood95 at ntlworld.com> 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 tou've lost the whole show. With two phases left, you
>> can usuallyy cobble up enough lights to keep going.
>>
>> I've had to dothis once when the isolator developed a mechanical fault.
>>
>> Three-phase machinery is a different question. Motors get awfully
>> confused if they lose one phase, so it is right for them.
>>
>> On 28 February 2015 at 15:11, Richard Niederberg via Stagecraft
>> <stagecraft at theatrical.net> wrote:
>> > Dear Tim,
>> > For Dimmer Packs, you should plug straight in to the breaker panel, so
>> > all
>> > the 'hots' trip together, if the breakers are mechanically interlocked,
>> > which they should be for maximum safety.
>> > /s/ Richard
>> >
>> > On Sat, Feb 28, 2015 at 7:00 AM, Tim Nielsen via Stagecraft
>> > <stagecraft at theatrical.net> wrote:
>> >>
>> >> Hey list,
>> >>
>> >> I have a L21-30 power supply mounted to the side of a breaker panel in
>> >> my
>> >> shop for a chain motor.  I've never used it, but lately on shows I've
>> >> found
>> >> myself in need for more power available on stage.
>> >>
>> >> I know Lex makes their "Bento Box"
>> >>
>> >> (http://www.lexproducts.com/products/entertainment/powerhouse-portable-distribution-boxes/20-30-amp-portable-distribution-boxes/30-amp-bento-box-with-tail-input-to-nema-receptacles)
>> >>
>> >> This looks like exactly the product I need, unless I'm overlooking
>> >> something.  Does anyone know about any other products I could use?
>> >> I've
>> >> seen a few adapter cables, but they all seem to output at 208v, which
>> >> isn't
>> >> useful to me.
>> >>
>> >> My plan would be to use it for power for bands on stage, occasional
>> >> extra
>> >> dimmer packs, running a couple of circular saws on stage, etc., not
>> >> constant
>> >> use.
>> >>
>> >> Thanks!
>> >>
>> >> -Tim
>> >>
>> >> --
>> >> Timothy Nielsen
>> >> Episcopal High School
>> >> Technical Director
>> >> Office:  (703) 933-4172
>> >> Email:  TDN at episcopalhighschool.org
>> >>
>> >> ____________________________________________________________
>> >> For list information see <http://stagecraft.theprices.net/>
>> >> Stagecraft mailing list
>> >> Stagecraft at theatrical.net
>> >> http://theatrical.net/mailman/listinfo/stagecraft_theatrical.net
>> >
>> >
>> >
>> >
>> > --
>> > /s/ Richard
>> > _________
>> >
>> > ____________________________________________________________
>> > For list information see <http://stagecraft.theprices.net/>
>> > Stagecraft mailing list
>> > Stagecraft at theatrical.net
>> > http://theatrical.net/mailman/listinfo/stagecraft_theatrical.net
>>
>>
>>
>> --
>> Frank Wood
>
>
>
>
> --
> /s/ Richard
> _________



-- 
Frank Wood