32Amp MCB tripping initially and then staying on when pushed back up?

[spagettilegs]

I have a 32amp MCB for my heating (heat pump) and when the heating comes on, it trips after a few seconds. If I push it back up it works fine until the next time the heat pump calls for power. I thought it might be faulty so I swopped it out but had the same issue with the new one.

What might cause this to happen?

Thanks

 

[davesparks]

Is this a new fault on an existing installation which has previously worked?

Or is it a fault on a new installation/something which has always happened since installation?

 

[spagettilegs]

Is this a new fault on an existing installation which has previously worked?

Or is it a fault on a new installation/something which has always happened since installation?

It's an existing installation thats worked fine for years...up until now.

 

[mainline]

It's an existing installation thats worked fine for years...up until now.

As @Dave said #5

Is the heat pump the only thing on this circuit ?

Look to see and test if there is a starter/run capacitor.

 

[davesparks]

It's an existing installation thats worked fine for years...up until now.

Then it's likely something is failing in the heat pump.

Was the replacement MCB exactly the same as the old one? Same rating, tripping curve, manufacturer etc?

 

[brianmoooore]

Sounds like the motor stiffens up when stopped, then the MCB hits the magnetic on first start, but draws that little bit less on the subsequent starts.
mainline's possibly failing capacitor would be worth checking.

 

[spagettilegs]

Then it's likely something is failing in the heat pump.

Was the replacement MCB exactly the same as the old one? Same rating, tripping curve, manufacturer etc?

I replaced it with like for like B rated 32amp. I tried a C rated. Same result. It's a 15Kw heat pump. Should I try a D rated? The max starting current is 74amps.

This is the motor being used. Compressor copeland zr72kce-tfd522, 1.242,61 € - https://www.skh-kaeltetechnik.de/Compressor-Copeland-Emerson-ZR72KCE-TFD522

 

[mainline]

I replaced it with like for like B rated 32amp. I tried a C rated. Same result. It's a 15Kw heat pump. Should I try a D rated? The max starting current is 74amps.

This is the motor being used. Compressor copeland zr72kce-tfd522, 1.242,61 € - https://www.skh-kaeltetechnik.de/Compressor-Copeland-Emerson-ZR72KCE-TFD522

If it worked fine before, then there is a fault which needs repairing.

 

[brianmoooore]

This is a 3 phase motor, so presumably a 3 pole MCB. I think most of us had assumed single phase.
Won't be any capacitors or start windings.
Possibly one faulty phase winding? Check the currents in each phase for balance, with a clamp meter