RCD (RCBO) use with Autotransformer

Q&A and troubleshooting
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1

Hi there, the power system on my boat is comprised of two 5K Quattro IIs in parallel (240V) into a 100A autotransformer. I would like to add an RCD (RCBO) breaker on the output 240V mains (L1&L2) but it blows when any load is applied. Is an RCD possible with an AT? What is the proper configuration?

Thanks!

2

you need 2 x RCD, one L1/ N, the other L2/N. This is because the Auto transformer adds a return path that is not monitored by the RCCD.

The other alternative is to add a 3 phase RCD, wiring only L1, L2 and N to the RCD (ignoring L3).