Crabtree cons unit feeds 4 circuits, want to add 2 circuits from old fuse box but c/u has no rcd protection. Is it ok to remove the main isolator and replace with 80amp 30m amp rcbo or does a double pole isolator have to be upstream in a consumer unit.
Crabtree starbreaker
- Thread starter JACKC
- Start date
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If I have understood correctly -
It's not ideal as one fault will take out everything.
Obviously a switch has to be upstream.
Why can't you fit RCBOs for the new circuits.
You mean RCCB, I presume.
It's not ideal as one fault will take out everything.
Not sure what you mean.
Obviously a switch has to be upstream.
Why can't you fit RCBOs for the new circuits.
Yep, RCBOs are your friend here
He hasn't specified what model/age it is - could it be one of the older obsolete units like the one I expect to be pulling out of my G/Fs house before too long ?
As to using an RCD as a main switch, aren't the technical requirements* for the main switch different to the switching requirements for an RCD ? I've sen pictures on here of CUs with a combined main switch and RCD - but I doubt an RCD not specifically designed for it would have the required features.
* I suspect forced contact opening might be one of them. As in, when you open the switch, it forces the contacts apart as opposed to forcing them closed when on and letting them spring open for off.
As to using an RCD as a main switch, aren't the technical requirements* for the main switch different to the switching requirements for an RCD ? I've sen pictures on here of CUs with a combined main switch and RCD - but I doubt an RCD not specifically designed for it would have the required features.
* I suspect forced contact opening might be one of them. As in, when you open the switch, it forces the contacts apart as opposed to forcing them closed when on and letting them spring open for off.
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Thanks for the replies, going down the line of just fitting new c/u and leaving Crabtree alone unless customer wants to pay for EICR on this board. Wasn't sure if a RCCB was suitable for replacement for main isolator. Forced contact reason sounds good enough not to do it.
Don't think so. Table 53.4.
Who would have fitted a main switch on a single RCCB board?
How is it 'combined' rather than just being an RCCB.
It is designed for it. That's what it does.
Wouldn't RCCB contacts be forced apart when it trips?
Well if (and note the IF, that's why I asked the question rather than made it as a statement) the RCCB normally used in a CU doesn't meet the requirements for a main switch, then having one that's designed to meet both sets of requirements would be a combined function device. The photo that comes to mind had an RCD/Main Switch that was perhaps 3-4 modules wide and was labelled "Main Switch" as well as it's RCD specs. None of the RCDs )other than that one) I;ve seen in CUs have been labelled as such.
Is it ? And RCCB is designed to disconnect the circuit when there's earth leakage, a main switch is designed to provide a certain level of isolation. The former might provide the latter, it might not, it would depend on it's design.
Not necessarily. The contacts will be opened by stored energy in a spring - whether that's sprung contacts or in the mechanism. If the contacts welded for some reason (closing onto a load for instance) then it's foreseeable that the stored energy might not be sufficient.
There's a huge difference in operating force between the main switch and the MCBs and RCDs I've seen in CUs.
That's why I asked the question. I'll look up the reference you gave next time I'm in the same place as my old copy of the regs.
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