curious about ratings on breakers as regards voltage

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bstoin

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I happened to notice that single pole breakers of various makes are rated for 120/240AC. My question is this: does this designation mean that a single pole breaker could be used on a high leg for special equipment?
I have seen posts on different occasions that would indicate that single pole breakers cannot be used on a high leg because "they are not rated for such uses," but the 120/240AC marked on the breaker would seem to indicate that they could be used on a high leg.
 
The 120/240 tells you that you cannot use that breaker on a high leg. You have to meet both conditions...1) not exceeding 240 volts hot to hot, and 2) not exceeding 120 volts hot to ground. If you install it on a high leg you have 208 volts to ground. A breaker that is suitable for use on a high leg will only have a 240 volt marking. See 240.85.
Don
 
Chris, you could use two of these breakers with an identified handle tie for a line to line load, see 240.20(B)(2)

Roger
 
chris kennedy said:
How would this occur on a single pole breaker other than a phase to phase fault?
Click to expand...

Two examples where slash rated breakers cannot be used are:
A 3 phase 4 wire 240/120 system has a high (wild) leg of 208V to ground.
A 3 phase 3 wire 240 delta corner grounded (grounded B phase) has 240V to ground.
 
The issue is what is the maximum voltage pole pole of a breaker must interupt.
withg a 120/240v rated breaker you would be looking at either a 120v 1ph3w or 208y/120v 3ph4w w/grounded neutral. a single pole on a 1, 2, 0r 3 pole breaker would never see over 120v. Then, as the others have pointed out you have 240v 3ph 3w deltas, 240/120v 3ph4wire deltas, 480v 3ph3w deltas, and 480Y/277v 3ph4w.
If you take a look at each system what is the maximum voltage a single contact by itself must be able to clear? This usually is representitve of a line-neutral or line to ground fault. When 2 or more contacts are involved in clearing a fault they are in series so there is double that contact gap to draw deionize and dicipate the arc.
 
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