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RCCB & Switch Overload Protection (536.4.202)

sparkiemike
Just trying to get my head around regulation 536.4.202, particularly the last line.


“However overload protection shall not solely be based on the use of diversity factors of the downstream circuits. To achieve overload protection of RCCBs or switches, the rated current of the OCPD shall be selected according to the manufacturers instructions”.


If I understand it correctly in a the sum of the downstream MCBs should not exceed the current rating of the RCD. So in most dual RCD split load boards the RCDs would need to be rated at 100A


Is this correct, because there seem to be a lot of "pre-populated" boards still being sold with 63A RCDs? 


How are others interpreting this new reg?
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    So it's sounding rather like things haven't changed much. If you're assembling things yourself (e.g. RCCBs in separate enclosures) then you follow traditional BS 7671 rules and have to ensure overload protection using an appropriately rated overload protective device (or possibly the sum of several downstream devices). If however you're using a pre-manufactured assembly (e.g. to BS EN 61439 series) than it's the rules of the equipment standard that apply and then one permitted option is complete reliance on diversity without an explicit overload protective device - provided the manufacturer can justify that. Or have I overlooked some subtlety again....?


      - Andy.

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  • 0
    So it's sounding rather like things haven't changed much. If you're assembling things yourself (e.g. RCCBs in separate enclosures) then you follow traditional BS 7671 rules and have to ensure overload protection using an appropriately rated overload protective device (or possibly the sum of several downstream devices). If however you're using a pre-manufactured assembly (e.g. to BS EN 61439 series) than it's the rules of the equipment standard that apply and then one permitted option is complete reliance on diversity without an explicit overload protective device - provided the manufacturer can justify that. Or have I overlooked some subtlety again....?


      - Andy.

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