3phase /220V in a new theatre

bdauterive

Member
Hello all,
I am thrying to convince our electircal contractor that our shop/ stage area needs to have a 220V/3phase company switch for touring groups and road shows instead of the standard 208V/3phase. Does this seem right or am I off my rocker?
 

coldnorth57

Active Member
Hi bdauterive,
welcome to CB
your elctircal contractor is right you want to have 208v/3phase
220v is not 3phase
 

museav

CBMod
CB Mods
Departed Member
I am thrying to convince our electircal contractor that our shop/ stage area needs to have a 220V/3phase company switch for touring groups and road shows instead of the standard 208V/3phase. Does this seem right or am I off my rocker?
120/208VAC, three phase is typical for company switches and power distribution devices, is there any specific reason that you believe you need a 220VAC company switch?
 

mrb

Active Member
you want the 120/208 WYE. There is no such thing as 220v in the usa. There is 240V 3ph Delta which comes in two flavors. Regular delta has 3 hots only and you will not get 120v from it. Then there is center tapped delta which is basically a 120/240v service with a third 240v leg. Also referred to as 'high leg'. The latter two are very common in So Cal, but you want 120/208 Wye service.
 

tjrobb

Well-Known Member
Well, we sort of have 220 3p. Our incoming is 220/127 for some strange reason. Then again, our building still has TWO phase power...
 

JD

Well-Known Member
Well, we sort of have 220 3p. Our incoming is 220/127 for some strange reason. Then again, our building still has TWO phase power...

Yea, I remember seeing a ~222 on a Wye box. Checked the neutral and got ~130 volts! Got a second meter, same thing. Got through the night, no failures (sound, stage, or lights) but it gave me the creeps! (Allentown PA)

Only about 9% high when you think about it, just wasn't expecting it at the time. (PECO usually is low, PP&L runs high here in PA)
 

mrb

Active Member
:grin:
How does two phase work? I didn't know that two phase is available commercially. You don't mean split-phase, do you?

two phase power has 4 hot wires, basically two seperate single phase windings that are in sync. Was used at the dawn of commercial power to run motors. I think niagra falls output 2 phase and I know it was used in san francisco. Most utilities have done away with it but there is a special transformer those with 2 phase equipment use to create it. Google Scott-T transformer.
 

JD

Well-Known Member
:grin:

two phase power has 4 hot wires, basically two seperate single phase windings that are in sync. Was used at the dawn of commercial power to run motors. I think niagra falls output 2 phase and I know it was used in san francisco. Most utilities have done away with it but there is a special transformer those with 2 phase equipment use to create it. Google Scott-T transformer.

Often "two-phase" power is simply two of the three legs off of the Wye. Sometimes, an old building that may have been Delta gets upgraded and what had been the single phase panels end up with the two-of-three.
 
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JD

Well-Known Member
no.

two hots off a 3ph service is considered single phase. Two phase is an entire different animal. Heres a wikipedia article on it Two-phase electric power - Wikipedia, the free encyclopedia

No.

It is considered to be bi-phase. Each hot is 120 volts to N, but only 208v is available between the hots as there is a phase lag between the hots. http://www.controlbooth.com/wiki/bi-phase Single phase would provide 240 volts with a 180 degree phase relationship.

The only time a 180 degree phase relationship is found off of a three phase service is in Delta applications where one of the 240 legs is center tapped. In that application, the 120-0-120 tapped leg is single phase.

As noted in the above discussion, Wye power was used.
 
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mrb

Active Member
No.

It is considered to be bi-phase. Each hot is 120 volts to N, but only 208v is available between the hots as there is a phase lag between the hots. bi-phase - ControlBooth Single phase would provide 240 volts with a 180 degree phase relationship.

The only time a 180 degree phase relationship is found off of a three phase service is in Delta applications where one of the 240 legs is center tapped. In that application, the 120-0-120 tapped leg is single phase.

As noted in the above discussion, Wye power was used.

oops youre right in that its not the same as single phase, but its still not two phase.

Should also be noted that the neutral on a circuit with 2 hots derived from a 3ph wye service carries more current than the phase imbalance and is considered a current carrying conductor.
 

tjrobb

Well-Known Member
We have a dry-type transformer that gets us 220V two-phase at 90d. Your "basic" converter. Sorry, but no rights to post photo.
 

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