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Three Phase RCD & MCB Wiring?

Nano Brewery
Please could somebody advise on the most cost effective procedure of wiring up RCDs & MCBs on a DIN Rail for independent circuit protection.  Tried Googling to no joy.  Plenty of Single Phase advice, images, videos.  If using 4 Pole MCBs & RCDs, would I be correct in assuming that similar to single phase, it's just a case of Busbar-ing the MCB Lives to the RCD Lives and taking the RCD to Neutral Bar?


Have seen diagrams (like below) where the Incoming L1, L2, L3 get split to separate DP MCBs, RCDs and SP MCBs for each phase.  Seems like a bit of a faff and a pricey option (3x DP MCBs + 3x RCDs + 3x SP MCBs) per circuit.


I have 3x Three Phase Circuits (13A, 40A, 48A) that I wish to protect independently with RCDs.


Thanks in advance!  Dan.

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    davezawadi (David Stone):

    No Ebee that is not correct, any load on any phase is satisfactory, if you think about it any drop in N current is reflected in the other phases. It is the sums of all of them together which causes the trip. It may be slightly difficult to see but remember the 3 phase are all 120 degrees apart so sums ar not quite so simple, including the N current which will probably be out of phase with all the live phases. The result is exactly the same as a single phase RCD, the lack of exact summation is what causes the trip.


    Good. I was wondering which one of you would spot that little gem! (As Captain Mainwaring used to say)


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  • 0
    davezawadi (David Stone):

    No Ebee that is not correct, any load on any phase is satisfactory, if you think about it any drop in N current is reflected in the other phases. It is the sums of all of them together which causes the trip. It may be slightly difficult to see but remember the 3 phase are all 120 degrees apart so sums ar not quite so simple, including the N current which will probably be out of phase with all the live phases. The result is exactly the same as a single phase RCD, the lack of exact summation is what causes the trip.


    Good. I was wondering which one of you would spot that little gem! (As Captain Mainwaring used to say)


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