FPE 100 amp Three Phase Breaker tripping

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powerplay

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Electrical Contractor
I have heard FPE breakers tend not to trip easily at times, but in an old upstairs Meter Stack the Three Pole 100 amp Breaker trips when an existing old circuit from the downstairs remote FPE loadcenter panel with 120 volt 15 amp breaker shorted out…. We’ll change the 15 amp breaker first I’m thinking, but seems odd an 100 amp breaker takes out the whole panel when the 15 amp breaker doesn’t trip?
 
powerplay said:
I have heard FPE breakers tend not to trip easily at times, but in an old upstairs Meter Stack the Three Pole 100 amp Breaker trips when an existing old circuit from the downstairs remote FPE loadcenter panel with 120 volt 15 amp breaker shorted out…. We’ll change the 15 amp breaker first I’m thinking, but seems odd an 100 amp breaker takes out the whole panel when the 15 amp breaker doesn’t trip?
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Thats because they are not selectively co-ordinated. :)
 
powerplay said:
I have heard FPE breakers tend not to trip easily at times, but in an old upstairs Meter Stack the Three Pole 100 amp Breaker trips when an existing old circuit from the downstairs remote FPE loadcenter panel with 120 volt 15 amp breaker shorted out…. We’ll change the 15 amp breaker first I’m thinking, but seems odd an 100 amp breaker takes out the whole panel when the 15 amp breaker doesn’t trip?
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Actually it's quite common for a short on a 15 or 20 amp branch circuit to trip a 100 amp main upstream. Actually just had that happen a couple weeks ago where a 125 amp breaker in a meter center tripped from a short on a branch.
 
If the breaker shorted out as you stated then yes the feeder OCPD should have opened ( tripped).
It do what it was supposed to do.
I take it that this is a main lug panel.
 
Is there a possibility this old Main Lug Loadcenter FPE NA breaker is faulty and and that replacing with a new NA 15 amp breaker it may respond first ?
 
Where you have a high available fault current on the load side of the smaller breaker, it is very common for the upstream feeder of service breaker to trip. This happens where the current at the fault is in the instantaneous trip region of both devices. Without the use of expensive electronic breakers, you cannot expect selective coordination for breakers between 15 and 200 amps or so.
 
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