Vynckier MCB compatibility

[JohnW2]

Yes I meant my post on discrimination. (I just typed diversity again, don't know why I have that word in my brain)

Fair enough.

As for the RCD, it needed to be introduced for the circuit in the shed and I was merely pointing out that this had been considered (before anyone pointed it out). And as for the location it's just convenient to have it at the CU rather than fit one in the shed.

Yes, your socket(s) must have RCD protection. Although it's not quite 'discrimination' in the usual sense (which most commonly refers to discrimination between two protective devices), there is a related issue ('separation of circuits') here. If you have the RCD at the house (or, indeed, on the incoming supply at the shed), then a fault on the shed sockets circuit which caused the RCD to trip would take out the shed lighting as well - which some people would regard as dangerous. On the other hand, if you had the RCD in the shed, and only protecting the sockets circuit (not the lighting), that problem would not arise.

Kind Regards, John

 

[oo7]

I understand the potential danger with the RCD taking out the lighting but an emergency light has been included in the design to cover this.

So that's my current design but if I went for a small rcd protected CU it the shed I would need to up the CSA of the SWA to incorporate a larger fuse covering the SWA (which would be required to discriminate between the fuse protecting the SWA and the 32a fuse in the shed CU?) Do you see what I'm trying to say?

Good dame it, I hate trying to explain things in writing.

 

[JohnW2]

I understand the potential danger with the RCD taking out the lighting but an emergency light has been included in the design to cover this.

Fair enough.

So that's my current design but if I went for a small rcd protected CU it the shed ....

That would leave you with same same problem of needing emergency lighting, because the RCD in that CU would be protecting both the sockets and lighting circuits.

... I would need to up the CSA of the SWA to incorporate a larger fuse covering the SWA (which would be required to discriminate between the fuse protecting the SWA and the 32a fuse in the shed CU?) Do you see what I'm trying to say?

Yes, I do understand what you're trying to say, but I think you're missing something. What you say is only true because you are thinking about a mini-CU which has MCBs/fuses as well as an RCD. If you had just an RCD protecting just the sockets circuit (with lighting coming off the supply before the RCD, via an FCU). then you would not have the problem to which you refer since there would be no fuse/MCB protecting the sockets circuit in the shed.

Kind Regards, John

 

[oo7]

Apologies for my lack of experience and knowledge but are you saying you can fit a circuit direct into a RCD (giving it no over current protection after the RCD because in this case this would be at the main CU)? I've not seen or heard of this done.

 

[JohnW2]

Apologies for my lack of experience and knowledge but are you saying you can fit a circuit direct into a RCD (giving it no over current protection after the RCD because in this case this would be at the main CU)? I've not seen or heard of this done.

Yes. The circuit would still have the required over-current protection - the fact that it was 'before' an RCD makes no difference. I agree that it's not a very common situation, but I can see nothing wrong with it.

Kind Regards, John

 

[oo7]

Apologies for my lack of experience and knowledge but are you saying you can fit a circuit direct into a RCD (giving it no over current protection after the RCD because in this case this would be at the main CU)? I've not seen or heard of this done.

Yes. The circuit would still have the required over-current protection - the fact that it was 'before' an RCD makes no difference. I agree that it's not a very common situation, but I can see nothing wrong with it.

Kind Regards, John

Well it's "out of the box" thinking but like you say there's nothing wrong with it. Thanks, you've opened up a new world of wiring to me.

But on the other hand I can't see anything wrong with sticking the whole circuit (include the SWA) on the RCD protected CU providing the emergency lighting is included.

 

[JohnW2]

Well it's "out of the box" thinking but like you say there's nothing wrong with it. Thanks, you've opened up a new world of wiring to me.

You're welcome. The current which goes through an RCD is obviously the same on both 'sides' of the RCD, so it doesn't matter which side the over-current protection is. All that matters is that the OPD is upstream of all the cable it is protecting.

But on the other hand I can't see anything wrong with sticking the whole circuit (include the SWA) on the RCD protected CU providing the emergency lighting is included.

Nor can I, other than the 'inconvenience' of possibly having to go from the shed to the house to reset the RCD. The 'loss of lighting' is really the only safety issue - and, as I'm always saying, if the situation is such that sudden loss of lighting could present a danger, then one needs emergency lighting, anyway - the the lighting circuit itself (or the entire electricity supply) can fail, regardless of the wiring and protective device arrangements.

Kind Regards, John