# breakers and voltage question



## Wireman191 (Aug 28, 2011)

The voltage ratings are on the breakers.
Your breaker rated for 240V will be fine with 208V But if it was rated for 208V you cannot exceed that voltage for that breaker.


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## kbsparky (Sep 20, 2007)

No real difference when installing a standard 2-pole breaker into a 3 phase 208Y/120 Volt panel.

BIG difference when installing a 2-pole breaker into a delta-connected 120/240 3 phase panel, where one of the connected phases is a "high leg." In this case, you would need to have a straight 240 Volt rated breaker (instead of a 120/240 Volt rating).


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## Bad (Oct 13, 2011)

I didn't even know 2 pole breakers had a 120v rating.


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## Wireman191 (Aug 28, 2011)

I had to look, I have a Square D breaker right in front of me and could have sworn they were all rated to 277V, This one is only rated to 240V:blink:


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## Roger123 (Sep 23, 2007)

kbsparky said:


> BIG difference when installing a 2-pole breaker into a delta-connected 120/240 3 phase panel, where one of the connected phases is a "high leg." In this case, you would need to have a straight 240 Volt rated breaker (instead of a 120/240 Volt rating).


I have read this a number of times, what is the difference?


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## Norcal (Mar 22, 2007)

Roger123 said:


> I have read this a number of times, what is the difference?


 
Because the lower rating on a 120/240V slash rated breaker is lower then the supply voltage (208V high leg).


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## micromind (Aug 11, 2007)

A breaker with a slash rating (120/240) can interrupt its AIR current of the lower voltage across one pole. It can also interrupt its AIR current of the higher voltage across two or more poles, but not one pole.

A breaker with only one voltage rating can interrupt its AIR current across one or more poles.

With a 4 wire ∆ system, more than 120 volts exists from the high leg to neutral or ground, so a 120/240 breaker cannot be used with the high leg, but a straight rated 240 volt breaker can.


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## Big John (May 23, 2010)

I never thought of that. I always vaguely assumed it had to do with insulation clearances between poles or to ground or something. I didn't think it would affect the interrupting ability.

-John


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