You are quite right in saying that the RCD is strapped out.
The reason this came to my attention was an electrician working about half a mile away from this site was changing an RCD in a domestic property and noticed that there was 113V earth to neutral and 353V earth to phase.
After several hours of checking and testing other properties, supply cables and overhead line connections we got to the end of the line. I removed his yellow phase distribution fuse from the cut-out and the problem disappeared. As the RCD had been strapped out, the fault was feeding back onto our network.
Because of the nature of the site, we agreed to help the owner locate the fault. The whole place was an absolute nightmare.
The switch on the bottom left feeds the sub-main cable which runs up to the pig sheds. At the other end is a fuseboard with 3 fuses in, and then everything is fed out on 2.5mm2 twin and earth with unfused cooker switches used to isolate different sheds!
Needless to say, he got a severe ear-bashing and has promised to sort this mess out. I will be going back soon...
