120 volt loads on 480/277v gear.

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I'm guessing this is just plain fail:mad::D , has anyone actually load tested a situation like this ?

I have stumbled on a situation where a panel is 480/277 and the loads associated are 120/208.

My assumption is that the interior wiring will potentially be subjected to extreme overload.

I'm thinking a 277v breaker with a supply voltage or 120 volts would not trip until it carries 45 or 50 amps, Am I wrong ?

By the way , I have not taken off the deadfront and verified the breakers to be 277, but they appear to be, and the panel is definitely labeled 480v....

:-?
 

LEO2854

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I'm guessing this is just plain fail:mad::D , has anyone actually load tested a situation like this ?

I have stumbled on a situation where a panel is 480/277 and the loads associated are 120/208.

My assumption is that the interior wiring will potentially be subjected to extreme overload.

I'm thinking a 277v breaker with a supply voltage or 120 volts would not trip until it carries 45 or 50 amps, Am I wrong ?

By the way , I have not taken off the deadfront and verified the breakers to be 277, but they appear to be, and the panel is definitely labeled 480v....

:-?
Are you looking at a 480/277 volt panel that feeds through a 480 volt step down transformer to a 208/120 panel?
Need more info!
 

hurk27

Senior Member
We have a theater with a 480/277 volt GE 2000 amp MDP feeding a 900 amp breaker feeding a 750kva transformer that feeds another 2000 amp 208/120 volt GE MDP, both MDP's are the exact same including the 480/277 label, I asked the GE engineer if this violated there listing, he said no because the same breaker gets labeled for both voltages, when I brought up that the NEC required that if it is labeled for 480/277 it wouldn't be allowed on a 208/120 he just said he will have the plant send the correct labels, but he said the breakers are exactly the same?:confused:

I left it alone as it didn't seem to be a factor to him.

As far as tripping, breakers react to amperage not voltage, so the tripping point should not change, but the contact rating would change, but that would be when using a 120 volt breaker for 277.

I should add that all the sub panels in the place on the 208/120 side were also labeled for 480/277 also.
 
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Jraef

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As mentioned, breaker tripping has nothing to do with voltage, only current. Voltage is important only with regards to spacing of components, i.e. 480V components need to be spaced further apart to avoid flashover. So a breaker rated for 480V is perfectly fine with anything lower than that. But the converse is not true; if a breaker says on its nameplate that it is rated for a maximum of 240V, you cannot apply 480 (or 277) to it.
 

hurk27

Senior Member
As mentioned, breaker tripping has nothing to do with voltage, only current. Voltage is important only with regards to spacing of components, i.e. 480V components need to be spaced further apart to avoid flashover. So a breaker rated for 480V is perfectly fine with anything lower than that. But the converse is not true; if a breaker says on its nameplate that it is rated for a maximum of 240V, you cannot apply 480 (or 277) to it.

you know I asked that GE engineer if it would affect the GFP or the auxillery units, and he said no, that the power supplys in them were rated to operate from 120 through 480, I was suprised.
 

dbuckley

Senior Member
I have stumbled on a situation where a panel is 480/277...
There is an inexactitude here.

Which of these is true:

*This is a 480/277 rated panel fed with 480/277 volts?
*Is it a 480/277 panel fed from something other than 480/277 supply, and if so what?

Without this item of detail, everything else is guesswork, and as Pierre notes, it'll get us nowhere.
 
Thanks a million guys,

I imagined the ratings would be based on load period, volt-amps, this seemed like a possible wire melting arrangement.lol

I'd not be comfortable with allowing the interior branch circuit wiring (12thhn) to be potentially loaded to 40+amps.

Since that's not the case and it's not a fire / life safety issue, I'm not going to change it out.


:)
 
...

Without this item of detail, everything else is guesswork, and as Pierre notes, it'll get us nowhere.


"...I'm thinking a 277v breaker with a supply voltage or 120 volts would not trip until it carries 45 or 50 amps, Am I wrong... ?"
 
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infinity

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The 277 volt breaker will have a higher AIC rating. Depending on the system they could be required. We have used GE 277 volt CB's when the engineer spec'd 65K AIC breakers. The 120 volt CB"s were only available in 10k and 22k AIC.
 

Jraef

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you know I asked that GE engineer if it would affect the GFP or the auxillery units, and he said no, that the power supplys in them were rated to operate from 120 through 480, I was suprised.
It's a relatively new development that is fairly common now with little Switch Mode Power Supplies.
 
The 277 volt breaker will have a higher AIC rating. Depending on the system they could be required. We have used GE 277 volt CB's when the engineer spec'd 65K AIC breakers. The 120 volt CB"s were only available in 10k and 22k AIC.

So it may be possible that this particular application was actually engineered this way?
 

infinity

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So it may be possible that this particular application was actually engineered this way?

I can only comment on that I've seen this done intentionally for the reason that I posted. We had two new panels to install, 208Y/120 volt, and they both came in with SP, 277 volt, 65KAIC breakers installed. When I contacted the switchboard manufacturer he stated that the EE had spec'd 65KAIC CB's. I'm unsure if their 65KAIC rating is even applicable at 120 volts.
 
I can only comment on that I've seen this done intentionally for the reason that I posted. We had two new panels to install, 208Y/120 volt, and they both came in with SP, 277 volt, 65KAIC breakers installed. When I contacted the switchboard manufacturer he stated that the EE had spec'd 65KAIC CB's. I'm unsure if their 65KAIC rating is even applicable at 120 volts.

Absolutely.

Many manufacturers have similar product ratings.

Hey much appreciated guys , this saves me from running a load test, and I'll sleep better...

Big help.

:)
 
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