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Sizing of RCBO

FusionControlEng

Hello All

I have been given the tasks of the sizing of an RCBO for 20 x 13A sockets, I am very new to electrical services design 

Obviously, the size of the RCBO will not be 260A  as this would assume all the sockets will be pulling 13A all at the same time which is very unlikely to happen

Is there a basic methodology for sizing an RCBO?

Many thanks

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  • 0

    For an RCBO (or indeed any means of 30mA RCD protection) also consider protective conductor currents - i.e. "earth leakage" in normal use (very common from things with electronic power supplies for example). Generally you'd want to keep normal leakage below about 30% of the RCD's rating (they can validly trip anywhere between 50% and 100% of their nameplate residual rating) - so below 9mA for a 30mA RCD. So if you were supplying say an office full of PCs or the like - which at a rough rule of thumb might leak 1mA each - you might want to limit the number of sockets per circuit to something closer to 9 or 10 rather than 20. Or have a larger circuit without RCD protection and RCDs local to each socket or small groups of sockets (often the case with underfloor bus-bar trunking systems).

       - Andy.

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  • 0

    For an RCBO (or indeed any means of 30mA RCD protection) also consider protective conductor currents - i.e. "earth leakage" in normal use (very common from things with electronic power supplies for example). Generally you'd want to keep normal leakage below about 30% of the RCD's rating (they can validly trip anywhere between 50% and 100% of their nameplate residual rating) - so below 9mA for a 30mA RCD. So if you were supplying say an office full of PCs or the like - which at a rough rule of thumb might leak 1mA each - you might want to limit the number of sockets per circuit to something closer to 9 or 10 rather than 20. Or have a larger circuit without RCD protection and RCDs local to each socket or small groups of sockets (often the case with underfloor bus-bar trunking systems).

       - Andy.

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