BS EN 61439-3 - what it actually says vs what people think it says

[JohnW2]

BS7671 (as do others) refers to other standards in several places, IMO to fully comply you need to have these standards also (when they apply).

As I said, I do not think that is really the case with 'Product Standards' (which is what most Standards are). In the case of a Product Standard with which BS7671 requires compliance, I would say that all that is required (or, indeed, all that is possible) is that the manufacturer of the product 'confirms' (i.e. by 'marking', and in the spec) that the product is compliant.

As I said, there's really no point in someone working to BS7671 looking at Product Standards, since there will almost never be any way in which they can confirm for themselves that a product they are using complies with the requirements of that Standard - they have to "take the manufacturers word for it".

As I also said, BS7671 is pretty unusual in being a 'what to do' Standard, rather than a Product one. Indeed, I'm pretty sure that my late father, a Standards Engineer, would have said that it was not 'a Standard' at all, but rather a set of regulations (and would probably draw my attention to the fact that it was subtitled "The IET Wiring Regulations" ).

There may be some Standards with which BS7671 requires compliance which are not Product Standards, but there can't be many, if any.

Kind Regards, John

 

[davelx]

I continue to be fairly amazed. Even if the TN-S sheath had only the same impedance as the L conductor (which I rather doubt), that would presumably require at least 50mm² cable all the way from the substation to your installation. I must say that I had always assumed that the 'extraordinarly high' PFCs we hear about would/could only ever be seen with TN-C-S.

Anyway, even 0.1Ω only equates to 2.3kA, and we are talking about 'greater than 6kA' - which I find hard to believe would ever be seen in a domestic installation.

Kind Regards, John

Coincidently, I had reason to do a Ze measurement this morning.
We are on clay with underground streams in the area, so the ground is always wet. also water pipes running parallel to the undergrpund cable pretty much all the way to the sub station, which might have an impact.

 

[JohnW2]

Coincidently, I had reason to do a Ze measurement this morning. We are on clay with underground streams in the area, so the ground is always wet. also water pipes running parallel to the undergrpund cable pretty much all the way to the sub station, which might have an impact.

That obviously will not affect the true Ze (i.e. without bonding connected) of a TN-C-S supply and I doubt that any amount of water will have much effect on the Ze of a TN-S supply, since the low impedance of the (metal) cable sheath will totally overshadow it.

With domestic TT, one would obviously be lucky to get a PEFC much over 6A, let alone 6 kA!

However, what might get overlooked is that PEFC (hence Ze) is only part of the story in terms of 'breaking capacity' of devices. PFC is the greater of PEFC and PSCC, and the latter will be dramatically greater (and the same as that with TN) in a TT installation.

Kind Regards, John

 

[SimonH2]

Coincidently, I had reason to do a Ze measurement this morning.

You can't leave us hanging - what results did you get for PEFC and PSCC ?

 

[davelx]

You can't leave us hanging - what results did you get for PEFC and PSCC ?

Didn't check, it was just a cursory test prior to splitting my tails (ooh err) for a feed to a new 32A EV charger. Will post the full results when I do the full tests for the EIC.