RCBO's trip on split phase 120v/240v when breakers are turned on with no load

DIY
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1

Hi everyone,

I am helping a friend finish off a split phase system on their boat. It consists of 2 x 24/5000/100 110v Quattros with shore power and generator feeds in. Each AC out L1 and L2, goes to a 40A 110v RCBO. They then pass to contractor and then to MCB’s rated for each circuit.

Turning the inverters on is fine, turning each RCBO is fine. Engaging the contractors is fine. When we turn a MCB on to test that circuit, the RCBO’s trip immediately. Even on a circuit with is just sockets.

We have buzzed everything through and cannot find an earth leaks, earth to neutral shorts.

Any pointers would be much appreciated.

2

Not quite the same scenario, but maybe the same underlying cause:

Recently rewired my MP2 installation and needed to swap out the RCBO on ACin. It was tripping when very small loads on ACout1 were switched. instead we now use a time-delay RCD on ACin and have no nuisance tripping.