400 amp breaker issues

[mboltz110]

we had a 400 amp breaker kick out twice in the past two weeks it goes to a 1200 amp main witch also kicked off when the 400 amp kicked off. I used my meter to check the load side of the breaker when it was off I have 3 volts on one of the phase or if I check phase to ground I get 3 volts on each leg of the 400 amp breaker when its off. is this a sign the breaker is going bad? any ideas would be appreciated.

thanks

 

[texie]

If it also tripped the up stream breaker you likely have an intermittent dead short.

 

[ron]

I used my meter to check the load side of the breaker when it was off I have 3 volts on one of the phase or if I check phase to ground I get 3 volts on each leg of the 400 amp breaker when its off. is this a sign the breaker is going bad? any ideas would be appreciated.

Depending on the meter you used, it could be phantom voltage. https://www.nema.org/Technical/Documents/Bull_88_reaffirmed_12_15_11.pdf
Do you have an analog meter you could try?

 

[mbrooke]

Capacitance can induce voltage.

 

[Cow]

If it also tripped the up stream breaker you likely have an intermittent dead short.

I agree with this.

Sounds like you may also have a coordination issue with your breakers.

We would be getting the megger out to try and track the problem down.

 

[mboltz110]

Ok, thanks everyone. I will get or megger out and try to track it down.

 

[jimport]

Just had one a week ago. A 250a was tripping with no load, <20a on it. The C phase had a hot spot that you could not touch.

 

[Jraef]

Ok, thanks everyone. I will get or megger out and try to track it down.

Seemingly random intermittent trips like this are often associated with moisture somewhere, so if you can, megger when known to be dry and then again when possibly wet, comparing the readings. If there is a significant change, that’s your likely culprit and may indicate failing conductor insulation.

But it as mentioned, you appear to have a coordination problem too if the 1200A breaker is tripping before the 400A. That needs to be addressed no matter what else you find.