I have a 4xmcb + 1 DP isolator switch in a CU. T Can I replace the switch with a RCD (which has a switch in it anyway)? I mean will it physically fit? They are both double-width devices afaik see but I haven't boughtthe rcd yet. All bits are contacum and the CU is only a year old - is has one of those rails that the devices clip onto.
If I can't do this I suppose I have to replace the whole unit? thanks
Yes a RCD will fit in as a replacement for the main switch. If you already have another RCD in the same enclosure and you wish to retain the "master switch" capability of the main switch position then the RCD selected will need to be a time delayed type since the other RCD will be cascaded from it.
Thanks John. The exisiting unit only has the switch and 4 mcb's. Saved me buying an rcb on spec. tvm
Physically yes but is an RCD considered acceptable as a "main isolator"?
Hager RCDs will fit contactum as well. Note that contactum changed design subtly a couple of years back - probably won't affect the RCD for switch swap - but to fit a new style MCB[1] in an old style enclosure requires a little copper adaptor to shim the live bus bar tab into the correct position.
[1] New ones have coloured dollys - colour depending on rating. Old ones were all brown.
Simple answer is yes, see Table 53.2 in 7671.
Regards Bruce
I guess I missed something here. I bought the new rcd and while the x-y-z dimensions are indeed the same the profile of the slot (thingy) for mounting on the rail is not. It could be the CU is older than I thought - that's the only thing I can think of anyway. Ah well. I see TLC sell an exclosure for rcd's - it'd be easier for me to get one of them than replace the entire CU & mcb's.
The DIN rail bit is usually fairly standard - its the relative position of the terminals that moves a bit...
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I was surprised at that too. Will get a pic of both the isolator slot and the rcd one.
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