your sub-main cable would only require RCD protection if part of it was, for example, T/E from CU buried or partially buried in a wall without earthed metallic protection.
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Discuss Multi RCD testing in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net
Time delay rcd LOL
a fluc apacitor should dit it as long as it's charged to 500V and clipped to his goolies.
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