120/208Volt Panelboard used on 240Volt supply

Status
Not open for further replies.
F

FaradayFF

Senior Member
Location
California
Hello All,
I had a question- are your typical 120/208Volt rated panelboard suitable for use on a 240V, 3 phase supply? If a slightly higher voltage is applied at the panel than what the nameplate rating of the panel is, will there be an issue? Is the spacing between phase bus bars, breaker voltage within a panel rating determine the volt rating of the panelboard? Does it also affect the footprint of the panel, otherwise a low voltage panel could have a nominal rating of 600Volt?
Thanks for your input.
EE
 
I think there are two answers.

It will probably work safely on 240 V 3 phase.

If it is not listed for it, you would be in violation of the code to use it that way.
 
petersonra said:
I think there are two answers.

It will probably work safely on 240 V 3 phase.

If it is not listed for it, you would be in violation of the code to use it that way.
Click to expand...
UL lists panelboards for their maximum voltage.
The issue of saying 240V 3 phase deals with the voltage to ground and generally affects the breaker selection not the panelboard interior/bussing. It is not uncommon to find installation restrictions on corner grounded systems.

I have never heard of a major manufacturer that regularly made max rated 208V breakers as it would not be cost effective when a 240V design is much more marketable.
 
petersonra said:
He didn't ask about circuit breakers. Just panel boards.
Click to expand...
Have never seen a panelboard with a 208 voltage rating...all I have seen are 240 volt rated, permitting use on either system and even on a corner grounded or high leg 240 volt delta system...of course you need straight rated breakers for the delta systems.
 
FaradayFF said:
Hello All,
... Is the spacing between phase bus bars, breaker voltage within a panel rating determine the volt rating of the panelboard? ...
Click to expand...
Low Voltage bus spacing is based on being UP TO 300V, then UP TO and including 600V. So there would be no difference between 208V and 240V.

As mentioned, the difference will be in the breakers. In a 208V 3 phase (presumably 4 wire) system, the maximum voltage reference from any phase to ground is 120V, so an asymmetric (ground) fault can only have the energy in a 120V source, meaning the breaker has an easier time interrupting it. In a 240V 3 phase system, those phases will be 240V reference to ground*, so the amount of energy in an asymmetric fault is greater and the breaker must be rated to handle that. So the difference is in what are called "slash rated" breakers, meaning 120/240V, or "straight rated" breakers, meaning 240V only, no 120V. Slash rated breakers are less robust, ergo cheaper than straight rated breakers. So a panel might be rated for 240V in terms of the bus bar voltage rating, but the breakers on a 120/208V system will be different than those on a 240V 3 phase delta system.

*Of course, a 120/240V 3 phase 4 wire "high leg" system mixes things up a bit, to where you can use the slash rated breakers on the two legs that are 120V to ground, but you still have to use straight rated breakers on that 3rd phase (usually B phase). Some panels restrict you from plugging single pole breakers into the spaces for the B phase.
 
FWIW, for Siemens panelboards there is a different letter in the part number for voltage and system type, "C" for 120/208 and "B" for 120/240 three phase 4 wire. I highly doubt there is any difference in the panel boards, probably just a labeling difference perhaps.

For load centers, every load center I have ever seen specifically says suitable for either system.
 
Status
Not open for further replies.
Top