Inverter board

Hi there I was wondering mcb keeps tripping, windings are ok not mechanical seized I was wondering would my inverter board trip the breaker if faulty the second I turn isolator at outdoor mcb trips at mains

On what system? I assume an AC system and not a VSD?

If you mean on an AC system then yes it could do, especially if the noise filter board has also failed.

Yes on a/c system it's a 3 phase compressor first I thought short circuit or grounded but resistance on windings are good I had 2.5 ohms across each winding and carried out megger test so then I thought mechanical but it's tripping even before compressor is called for.

what type of breaker ? b type typically for lights and sockets c an d type for ac units /motors- will take more of an inrush

You have checked the 3 phase rotary isolator haven't you? There could be a dead short in there, maybe water has got in.
It's worth confirming that first.

It's an c rated breaker..I need to call back and go through everything as I don't believe my compressor is causing the fault.is it possible winding insulation it badly damaged making compressor pull more current without giving me a short circuit or ground reading that there about to go.

If the winding insulation was bad, you would have picked it up on the insulation and resistance test.

Why not disconnect the compressor terminals to rule the compressor out for certain.

Il have to do that in the morning first thing and go form there.thanks for the help

inverter would detect overcurrent before a breaker trips

Ended up being inverter board and noise filter blown.i disconnected compressor still tripping