Cabling a remote RCD and using it as an isolator switch

AndyRob · Sep 6, 2021

I am drawing up a contract for a job in a domestic property which has a 3-phase Distribution Board and need to supply 3ph to a heat pump that's in the same room. An MCB in the DB will feed an RCD in its own enclosure, mounted next to the heat pump 3 metres away. I know that an RCD is desirable but have been told by some that it is an 18th Ed requirement too - but by others that it is not.

So, first, am I right in thinking that the 3m cable to the RCD has to be SWA, or standard cable in steel conduit, because the cable itself isn't protected by an RCD?
If the heat pump were in an outbuilding I appreciate that, under the 18th Ed, it would be normal/required to feed the RCD via SWA from the DB - but if the pump is nearby and in the same room?

Second, is their any reason why the RCD should not be used as the manual isolator for the heat pump, bearing in mind it can be located alongside? It would be easy to specify a larger enclosure to house both a dedicated isolator and the RCD with it, but would it be necessary? I'm sure I've seen spec's for either MCBs or RCDs (Hager maybe?) that promote the fact that their breakers can be used as isolators. Is it BS EN61008 that's the key?

Many thanks.

telectrix · Sep 6, 2021

So, first, am I right in thinking that the 3m cable to the RCD has to be SWA, or standard cable in steel conduit, because the cable itself isn't protected by an RCD?

not necessary. RCD required only if cable is buried. if it's surface mounted no need. unless it's TT earthing and metal enclosures.

Dartlec · Sep 6, 2021

According to table 537.4, RCDs are suitable for isolation, emergency switching and functional switching

For RCDs to 60947-2 (Industrial applications mostly I think?), the note says they are only suitable for isolation if the device is marked with the symbol for isolation

whereas 61008 and 61009 are fine for all uses according to BS7671

As @telectrix says, the cable can be anything suitable if it's surface mounted (or >50mm from surface)

There may be other considerations re the environment etc that may factor into choice of cable and protection, if it's likely to be bashed etc - but that's more a good practise thing than necessarily a regulation.