[TZ] 3 phase power

[Broadcast List USER]

Many years ago I was one of six engineers at an AM/FM combo.  The  
record library was wall to near ceiling shelves full of LPs and 45s.   
I guess the outlets were just covered by the shelf units because the  
room wouldn't have passed code without outlets.  An extension cord was  
run for the Selectric that was used to make the cart labels.

The Assistant Chief decided that cover plate on the wall near the  
ceiling would be a fine place for an outlet.  He installed one, not  
questioning the reason the wires were yellow, grey, and green.  He  
plugged in the Selectric and it worked fine.  Normally, it was only on  
for a minute or two while someone typed a cart label, so there was  
never a problem.

Until... some jock left the typewriter on and left.  After some amount  
of time someone noticed smoke coming out of the record library.  The  
Selectric got so hot it actually caught on fire.  Thankfully those  
tanks were made of thick metal so the fire was mostly limited to the  
typewriter itself, though the smoke was another issue.

The Assistant Chief then had the idea of checking the Voltage on his  
outlet.  He couldn't believe it was 277 Volts.  Ultimately, I  
explained three phase power to him.  I really couldn't, but I then hit  
on an idea, ask him how we had 120 Volt AC at the transmitter site  
while the transmitters ran on 208.

--chip

On Jun 8, 2011, at 5:21 PM, Gary Glaenzer wrote:

>277 is to 480 phase-to-phase what 120 is to 208 phase-to-phase
>
>in other words, if you have a 480 Wye incoming, you have 277 each  
>phase to
>neutral
>
>very handy as you can run many more fluorescents per 20-amp breaker  
>as in a
>large store
>
>also neatly gets around the 'no greater than 300 volts between  
>adjacent
>devices in a box' restriction in the NEC
>
>From: "Steve Lewis" <steve at theengineeringbureau.com>
>>
>>Dare I ask about 277 volt lighting circuits?  I wasn't there at the  
>>time,
>>but an "electrician" once put a 120 volt florescent light fixture  
>>on a 277
>>volt circuit and when switched on apparently made for an  
>>interesting show
>>J