MEP003A opening main breaker at <75% load

[delvin00]

I need some guidance. My otherwise great MEP003A throws the main CB at 75% load as indicated by panel guage and my tester. I replaced the main breaker with a supposedly good one. Unfortunately it still does it. Where should I look next? Any help will be greatly appreciated.

 

[Munchies]

Could be a faulty Current transformer but thats a guess. double check your TM for this fault condition for some more clues. If that doesnt get you anywhere, read the mep-003a main breaker thread. Lots of info and measurements in there.
Lastly. Consider an oversized contactor to replace the breaker. They are quite troublesome.

 

[Harleyd315]

What is the amp draw at 75% load. Check it with an amp probe. I have had bad % load meters. Maybe a bad gauge and not bad breaker.

 

[LuckyDog]

You may want to check the adjustment of R3.IIRC If R3 is not adjusted correctly, it will cause the circuit breaker to trip at the wrong levels. Section 9 in TM TM 5-6115-585-34

 

[Isaac-1]

Also what is the history on this unit, could someone have swapped out the box with the CT in it from a MEP-002a and not reset it for a MEP-003a? just a thought as that trip point would be about right for a MEP-002a. Again the first thing I would check is that R3 is adjusted correctly since this breaker does not trip like a conventional breaker, instead it relies on shunt tripping from the CT circuit.

Ike