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I have a building that is mains supplied, but has a 3 phase back up generator-- black outs are almost daily here. There is no 3 phase equipment in use.

The current instillation is about 12kva, but the 4 pole RCD being used is too small. We don't have access to a shop to buy one for a wile....

Should I just use 3 individual RCD's, One on each Phase? Or use the existing 3 phase RCD and branch some loads off before it and give them their own single phase RCD?

Right now their solution was to just bypass the RCD for some loads, not ideal! This came to light when I tried to switch a load to another phase to get the loads balanced better to keep the genset from overloading. the RCBO would trip no matter what I did, and I eventual realized what was going on, and why there were 2 neutral buss bars.

Nothing is labeled so it is a bit of a frustrating job. I need to get going up ASAP, and NEED it to be safe as well. But need to do it with what i have on hand.

SV Savannah
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  • This sounds like a job for the Home Improvement crowd. – vir Jan 27 '22 at 00:05
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    I’m voting to close this question because it should be migrated to DIY.SE – Elliot Alderson Jan 27 '22 at 00:38
  • This is an electrical design question. It is in this context NOT about regulations but about using available equipment to achieve a safe design. – ATCSVOL Jan 27 '22 at 19:00
  • @SV Savannah An informal answer. You obviously understand the issues. Either if your suggestions sound "safe enough" properly implemented. I can't immediately think of disadvantages either way but I suggest looking at each possibility and trying extensive "what if ..." thought experiments to see if anything unsafe comes to mind. – ATCSVOL Jan 27 '22 at 19:05

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The key rule with RCDs is that current that goes out though a RCD MUST return through the same RCD.

So if you use one 3 phase RCD you can share a neutral between the phases downstream of said RCD. If you use separate single phase RCDs then you must keep the neutral downstream of each RCD separate.

It's difficult to give more specific advice without knowing both the regulations in your country and the design of the distribution equipment in use.

Peter Green
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