480 v. 277 V clarification?

[cmrobin21]

Hello,

I'm a relative newbie in the industry. I often look at panel schedules and wonder what the actual voltage of certain equipment is.

Say I'm looking at a panel schedule and I see equipment being called out as 3 phase, is this automatically 480V? Would 2 phase be 277V? I would think that I'd need to know whether it was a Delta of Wye configuration to know this.

What about single v. double pole? Is this an indication?

I'm most often confused when it comes to lighting...

Anyone know of a good resource to clarify any of this?

 

[mpparent]

If your incoming is 480/277V, 3ph, 4W (this means 3 hot or phase wires and 1 neutral(the ground is implied)), then if you had, say, a 20A/1p(pole) breaker, then it would be a 277V circuit. If it was a 2 pole breaker, then it would be 480V, 1ph. If it was a 3 pole, then it would be 480V, 3ph.

Any basic electricity book should give you some help with this.

Hope this helps,

Mike

 

[wbd]

3 phase does not automatically mean 480 v. 208 V is also 3 phase. Voltages are designated as something like 277Y/480, 3 phase or 120Y/208 V 3 phase.
If your looking at a lighting panel (like what is in your house), it is usually single phase 120/240 V.
Some ways to detect 3 phase - the higher voltage will be the lower voltage times SQRT 3 and 3 phase is usually on a motor control center or switch.

The pole on a breaker is the contact for the circuit - a single phase circuit will be one pole, 2 pole is still single phase and 3 poles for a 3 phase circuit breaker.

wbd

 

[cmrobin21]

Thanks guys,

WBD, you hit the hail right on the head. I have a few 3 phase loads, but what I've read tells me it can be either 277 or 480.

I guess I'm looking to verify the voltage with no vendor info, looking only at the panel schedule.

I contend that it's not really possible since delta/wye is not specified.

I guess I'll have to break down and find the exact requirements from each vendor!

Thanks again for both your responses!

CM

 

[davidbeach]

On a 480Y/277V system (not 277Y/480V, per IEEE definitions), you can have 480V single phase and 480V three phase, but you can only have 277V single phase. You can have 480V circuits, either single or three phase, that also have a neutral, but these are still 480V circuits.

The only way you would get 277V three phase would be a 277Y/160V system or a 277V delta, neither of which is very likely.