Switch Fuse Enclosures

[Aragorn84]

I guess in my case, the downstream device is a single 40A fuse, and so i should be fine with a 10mm link cable.


I guess where it gets less clear is the situation where its feeding multiple circuits, and in those situations its perhaps sensible to ensure the link cables can support the full current of the service fuse.

It just seems to me that the link cables in these wylex boards look quite small. It might be that infact they are larger than they look, and will happily support 100A.

Anyone seen them up close that can confirm the cable CSA used?

 

[mfarrow]

Probably very true in reality, but it's probably really a bit naughty to have a RCD rated at less that the total design currents of the circuits it protects. Let's face it, a couple of 32A sockets circuits could theoretically both be ('quite legally'!!) be fully loaded, before one started adding on other circuits, so a 63A RCD (pretty common in CUs) could easily be overloaded.

That's all very true, and I think the BS EN probably gives overload requirements for it for just that scenario. Plus one can then apply the whole installation diversity factors in the OSG, and we're laughing.

Wylex Standard has a system which allows devices above 30/32 A only in boards with 8+ ways. There is a tag on the shield which prevents it being screws into a 2/4/6 way board, which all have a 60A main switch.

 

[JohnW2]

I guess in my case, the downstream device is a single 40A fuse, and so i should be fine with a 10mm link cable.

Yes, I don't see that as a problem.

I guess where it gets less clear is the situation where its feeding multiple circuits, and in those situations its perhaps sensible to ensure the link cables can support the full current of the service fuse.

That would, indeed, seem sensible, given that I don't think the downstream OPDs could be guaranteed to give adequate protection to cables which were not already adequately protected by the cutout fuse.

It just seems to me that the link cables in these wylex boards look quite small. It might be that infact they are larger than they look, and will happily support 100A. ... Anyone seen them up close that can confirm the cable CSA used?

As you say, they might have higher CSAs (or, at least, CCCs) than appearances suggest. Are there no markings on the link cables?

Kind Regards, John

 

[Aragorn84]

Are there no markings on the link cables?

I've not seen one up close to tell.

This (albeit somewhat vague) suggests its 16mm:

http://community.screwfix.com/threads/wylex-consumer-unit-cable.53806/

I'll see whats in the cable bin at work, might be some offcuts of 16mm and if so i'll just use that.

 

[JohnW2]

That's all very true, and I think the BS EN probably gives overload requirements for it for just that scenario. Plus one can then apply the whole installation diversity factors in the OSG, and we're laughing.

That's all possibly true. What you say about diversity is much the same as my statement "probably very true in reality". Whether there is any sensible basis on which the Standard covering RCDs could allow for (potentially continuous) 'overloads', I'm not so sure, since the nature, arrangement and usage of circuits which an RCD protects will vary so much between different installations.

Wylex Standard has a system which allows devices above 30/32 A only in boards with 8+ ways. There is a tag on the shield which prevents it being screws into a 2/4/6 way board, which all have a 60A main switch.

True, but that is 'ancient history'. Virtually all modern dual-RCD CUs of any size will allow one to install MCBs or RCBOs the total 'rating'of which is far in excess of the rating of the RCD protecting them (and the Main Switch).

Kind Regards, John