Unusual Breaker Failure

[flashlight]

Service call for non-functioning commercial hot water heater. 208V 30A unit. Tested 110V to ground at both terminals of disconnect, but 0V between the two terminals. Checked phases at main panel, all OK. Circuit breaker for WH showed same thing, 110 to ground on both sides, but zero between poles. Somehow CB must have failed internally in such a way to pass one phase to both poles and cancel other--without shorting out. Replaced breaker, problem solved.

This is a new one on me--has anyone else ever seen this ?

 

[Smart $]

...

This is a new one on me--has anyone else ever seen this ?

Yes. One pole of breaker failed open. The "110V" reading you were getting on the load side of failed-open pole is the other phase through the load.

 

[flashlight]

Makes much more sense than what I said. I have old breaker, easy to verify. Thanks !

 

[Electron_Sam78]

We have around 500 RV electrical pedestals where I work which amounts to around 1500 circuit breakers that get turned off and on pretty regularly. I'm always changing out bad circuit breakers and have seen all kinds of failures including breakers putting out reduced or no voltage.