Delta Breaker Rating

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It needs to be 'straight rated' and more importantly it also needs to be rated for use on Grounded-B phase systems.

A rating 120/240V means the breaker can only be used where the maximum voltage to ground is 120V.
 
jim dungar said:
. . . and more importantly it also needs to be rated for use on Grounded-B phase systems. . .
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The UL White Book states that, "2-pole circuit breakers suitable for controlling 3-phase, corner-grounded delta circuits are marked 1? - 3? to indicate their suitability." However, if it were switching the neutral, a normal but full voltage rated 3-pole circuit breaker could be used. :)
 
I'm a little confused here, I have an ungrounded 240V delta system that is being used to feed heaters in this structure. A new fan forced heater was installed, there is a unit disconnect breaker rated for 120/240 on it, I ordered a new 2 pole 240V rated breaker to replaced the existing one, but I was thinking I really don't have L-G voltage since it's ungrounded right? So would the 120/240 breaker be ok?
 
Check NEC 240.85
Yiu have a situation with the potential of the breaker to see 240 to ground (if one phase becomes grounded) and the slash rating (240/120)indicates is is not listed for that possibility.
 
No wonder it seemed strange, I think Jim and I know I thought it was a corner grounded system. My (our?) bad.
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Definitely my mistake. Last night I read grounded, today I see it says ungrounded.

The first part of my answer remains the same, a slash rated (120/240V) device can not be used. Ignore the rest of my comment
 
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