480v on 208v buss

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JFletcher

Senior Member
Location
Williamsburg, VA
Short answer: no.

Long answer: 480 volts can either be 277 or 480 volts to ground. The breakers in that panel are rated 120 volts to ground. Even a straight rated 240v breaker cannot have 277 volts going to it.

My initial thought is such a setup would probably work fine until the first (or maybe 5th) time a breaker trips and then it would probably explode, and it wouldn't surprise me if the dead front gave way in such a blast. Everything in a 277 / 480 panel is beefier than its lower voltage counterpart.

Aside from academia, the only reason I think this question would be asked is if your client has an existing 208 panel that he wants to use for 480, and doesn't want to buy a new panel. If so, guess what, he gets to buy a new panel.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Did a service upgrade once, 277/480 400A. 200A to each of two units. One was a art studio type of space they were building out then, with glass blowing, welders, etc. They were doing their own electrical, but I had to go in there a few times for some GES stuff for the service. They used a regular 120/208 load center and fed it with 480. Hope its working out ok. :roll:

Now the opposite of this is not unheard of, using a 480 panel for 208. This may be done for systems with high fault currents since the AIC of a 480 breaker on 208 is typically pretty high.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Another thought back to the topic in the OP: Perhaps we should differentiate between the panelboard and the breaker. Take loadcenters and smaller panelboards where they will only take a given line of breakers and the 240V and 480 lines are not interchangeable. For example square D QO vs NF (EDB breakers), siemens Q vs BQD, GE 1" vs TEY......So even if the panelboard was ok with 480, the breaker wouldnt be. But many I-line breakers can and are used for both 240 and 480 systems. I am not sure if there is anything different about the panelboard itself for 240 vs 480. The dataplate would say a voltage, but that could just reflect what you said when you ordered it with the guts being the same either way. Other larger framed breakers are often the same in that you use it on both 208 and 480 systems, so the mounting is the same. Are the panelboard guts any different? I would take a WAG and say no, as they want to keep their component inventory as simple and universal as possible.
 
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wbdvt

Senior Member
Location
Rutland, VT, USA
Occupation
Electrical Engineer, PE
It is also a violation of NEC Article 110.4 which states that the equipment voltage rating shall not be less than the nominal voltage of the circuit to which it is attached.
 
kwired

kwired

Electron manager
Location
NE Nebraska
electrofelon said:
Another thought back to the topic in the OP: Perhaps we should differentiate between the panelboard and the breaker. Take loadcenters and smaller panelboards where they will only take a given line of breakers and the 240V and 480 lines are not interchangeable. For example square D QO vs NF (EDB breakers), siemens Q vs BQD, GE 1" vs TEY......So even if the panelboard was ok with 480, the breaker wouldnt be. But many I-line breakers can and are used for both 240 and 480 systems. I am not sure if there is anything different about the panelboard itself for 240 vs 480. The dataplate would say a voltage, but that could just reflect what you said when you ordered it with the guts being the same either way. Other larger framed breakers are often the same in that you use it on both 208 and 480 systems, so the mounting is the same. Are the panelboard guts any different? I would take a WAG and say no, as they want to keep their component inventory as simple and universal as possible.
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All I-line panels are built to same voltage standards. They are rated up to 600 VAC or 250 VDC. If you order a factory assembled panelboard they may mark it according to your specification, but is still built with same bus components. Not all breakers are rated for maximum bus rating though.
 
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winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Not going to disagree with the general consensus that a 208V panelboard is not suitable for 480V.

However IMHO this is not an outrageous question. We use 600V insulation for wiring, so your 208V wiring _is_ suitable for reuse at 480V. Many plugs and receptacles have voltage ratings that are higher than the NEMA configuration that they correspond to (eg. insulation other characteristics suitable for 480V but a NEMA 250V configuration). As electrofelon notes some panelboard mfgs use the same panelboards with different breakers for different voltages.

-Jon
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
We don’t know that it’s even “probably fine”. Aside from the breakers, panel bus and terminal separation and creepage distances are greater at 600V than at 300V, the two design and testing standards for gear. The panel mfr did not have to think about 600V separation when designing a panel to be listed and labeled at 240V. Neither would they have done fault with Stan /SCCR testing at the higher voltage, they didn’t have to. So for all we know, the bus bars are too close in that panel, regardless of the breaker ratings and even BEFORE the first breaker has to trip there may be serious problems. So saying “it’s probably fine” is potentially giving a nod to something that may catch fire. We have no way of knowing, so we should not even remotely condone this.

NO was a sufficient answer.
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Jraef said:
We don’t know that it’s even “probably fine”. Aside from the breakers, panel bus and terminal separation and creepage distances are greater at 600V than at 300V, the two design and testing standards for gear. The panel mfr did not have to think about 600V separation when designing a panel to be listed and labeled at 240V. So for all we know, the bus bars are too close in that panel, regardless of the breaker ratings and saying “it’s probably fine” is potentially giving a nod to something that may catch fire. We have no way of knowing, so we should not even remotely condone this.

NO was a sufficient answer.
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There is a difference between telling the truth about something and condoning it. It's like the inappropriate use of slash breakers. Probably never going to matter. Think about all the sites that have inappropriately rated equipment short circuit rating wise. Is there any evidence that this has resulted in any injuries? I am not aware of any.
 
Besoeker

Besoeker

Senior Member
Location
UK
Toros said:
Hi,
is it o.k to apply 480v to a panel that is rated (according to the name plate) for 120/208v ?????

Tanx
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I think a panel board is broadly similar to what we Brits (including the English :D) would call a control panel or sometimes a distribution board.
In such cases, the answer is an absolute and categoric and NO.
And it would

I'm not familiar with your NEC but be nothing short of astonished if it didn't contravene code not to mention invalidate any warranties.

IMHO of course........:D
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Jraef said:
We don’t know that it’s even “probably fine”. Aside from the breakers, panel bus and terminal separation and creepage distances are greater at 600V than at 300V, the two design and testing standards for gear. The panel mfr did not have to think about 600V separation when designing a panel to be listed and labeled at 240V. Neither would they have done fault with Stan /SCCR testing at the higher voltage, they didn’t have to. So for all we know, the bus bars are too close in that panel, regardless of the breaker ratings and even BEFORE the first breaker has to trip there may be serious problems. So saying “it’s probably fine” is potentially giving a nod to something that may catch fire. We have no way of knowing, so we should not even remotely condone this.

NO was a sufficient answer.
Click to expand...

For loadcenters and small panelboards I definitely agree. For larger panelbaords, if the breakers are rated for the higher voltage (or they are willing to replace them), it MAY be suitable for higher voltage, but one would have to check with the manufacturer.
 
Besoeker

Besoeker

Senior Member
Location
UK
electrofelon said:
For loadcenters and small panelboards I definitely agree. For larger panelbaords, if the breakers are rated for the higher voltage (or they are willing to replace them), it MAY be suitable for higher voltage, but one would have to check with the manufacturer.
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Too many "what ifs" and what about the equipment fed by the breakers?
 
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