I did write "if you are not using a CU you must ensure that your DB conforms to 61439-3 and meets 432.1".
And again, I point out that the standard for CUs is for distribution boards for use by ordinary persons, which will include all domestic installations.
16 kA.
You did, but it appears that if (in the scenario described in 530.3.4, including a reference to 'ordinary persons') one IS using it CU, it also needs to conform to 61439-3, and would also need to satisfy 432.1 (which appears to apply to any installation which has combined fault/overload protection devices, regardless who is 'in control' of it). So ......
I'm essentially asking what is the difference between the 'either' and the 'or' of BS7671's 530.3.4.
Yes - but, as above, 432.1 requires that the devices be able to be able to break the PFC of the particular installation. I don't really understand how the Standard can guarantee that the breaking capacity it requires will inevitably be at least as high as the PFC of any installation - unless, as I have suggested, the breaking capacity required by the Standard is so high that it's next-to impossible that any installation would have a PFC higher than that figure.
It is 16 kA.
If one is using a CU, then by definition it will conform to BS EN 61439-3. If it doesn't then it isn't a CU.
Ah, I see (I think). Either the assembly shall have an adequate prospective fault current withstand, or it shall withstand 16 kA.
I don't think it's necessarily that simple in the eyes of 7671. The 7671 definition of a CU does not mention any Standards, so presumably something could satisfy that definition, per se, without having to comply with any Standards, 61439-3 or otherwise.
I remain confused. Whichever of the 'either/or' (of 530.3.4) one chooses to use, the reg has a requirement that the devices conform to 61439-3, which you say specifies a 16kA breaking capability. That would mean that nearly all domestic installations would have to have 16kA (or higher) devices - something that I didn't think was the case (and seemingly similar with BAS, judging by his recent comment). As you go on to say, that would mean that 432.1 would only become relevant if the PFC were greater than 16kA - which I find rather hard to believe would ever be the case with the sort of installation that reg is talking about. As I've said before, although my experience is extremely limited, I don't think I've ever actually seen a PFC above (or significantly above) 1kA, let alone 16kA.
Maybe, but if that's what they are "trying to say", I don't think thet have been very successful. Furthermore, as above, I didn't think that such installations did need 16kA devices.
I might, but I don't really like making comments unless I have something constructive to suggest as a 'change' - and since I haven't got much of a clue as to what they are trying to say, I wouldn't really know what to suggest!
You tell me - although I wouldn't have thought so. The definition is almost laughable, and certainly not helpful:
BS7671 said:
Part 2 defines it as "A particular type of distribution board comprising a type tested coordinated assembly for the control and distribution of electrical energy, principally in domestic premises...".
If 530.3.4 applies, then either method of complying requires that the DB/CU complies with BS EN 60439-3
Shall I be generous and assume that you missed "including the conditional short-circuit test described in Annex ZA of BS EN 60439-3" by accident?
See above - do you really want to argue that when BS 7671 references a consumer unit it does not mean a type tested assembly complying with BS EN 60439-3, including the conditional short-circuit test described in Annex ZA of BS EN 60439-3?
I believe that the "conditional short-circuit test described in Annex ZA of BS EN 60439-3" relaxes that capability requirement. Basically, if you have a type tested coordinated assembly incorporating components and protective devices specified by the manufacturer complying with BS EN 60439-3, including the conditional short-circuit test described in Annex ZA of BS EN 60439-3, in an installation rated at no higher than 100A the devices do not have to be 16kA ones.
My recent comment was prompted by you saying that you don't have to worry about what 530.3.4 says about type tested CUs.
As with Ze, you can either measure the PFC or use the declared figure. AIUI the latter will be 16kA. If you want to use a lower figure you would, IMO, have to show what measures you had put in place to prevent that lower figure becoming incorrect through network changes outwith your control.
They are trying to say that you must either use
What devices does it use for fault & overload protection?
I think you'll find that 432.1 does.
When BS7671 references a "Consumer Unit" one has every reason to believe that they referring to the item which they have defined in Part 2 of the Standard. Indeed, if, despite it not being included in their definition, the term "Consumer Unit" implied "incorporating components and protective devices specified by the manufacturer complying with BS EN 60439-3, including the conditional short-circuit test described in Annex ZA of BS EN 60439-3.", there would be no need for them to qualify "Consumer Unit" with a repetition of those words in 530.3.4. If, as I now think is the case, they intended that it was a crucial part of what makes a DB a CU, they really should have included those qualifications in the Part 2 definition.
Yes, having done some reading I think you are right, my confusion having resulted from the fact that Stillp had told us that BS EN 60439-3 requires 16kA breaking capability. What he didn't do was mention that "conditional short-circuit test in Annex ZA", and it appears that that test allows the device, per se, to have a breaking capacity less than 16kA, but only if there is an upstream BS88-3 fuse ≤100A - the test being undertaken with a 100A upstream fuse.
Yes, that appears to be how the 16kA figure comes about. Mind you, assuming that your opinion is correct, and given that no-one could put such measures in place, they might just as well say that the devices have to be able to break the declared PFC.
Yes, I confess that I hadn't thought of that, but it makes me wonder what 432.1 is all about. That it requires that protective devices should be capable of breaking the PFC is fair enough, and little more than a statement of the obvious. However, under what circumstances does one have separate devices for protecting against overload and L-N faults?
I forgot to say ....
I don't see why you couldn't. Or at least I don't see why in your sort of situation one necessarily couldn't.
When I wrote that I knew full well what the significance of not having a type-tested CU was.
Yes, that's very much my situation (see **). My actual situation is that one phase serves the ground floor and cellar, the second phase serves the first floor and the third phase serves the second floor and outside stuff (garage, garden etc.). There are lots of CUs - 2 on first phase, 3 on second phase, 2 or third phase, and one little one for genny-only circuits. When we first moved in, an electrician tried to persuade me to have one or two 3-phase sockets in the cellar (my 'workshop') and garage, just in case I ever acquired a need, but I never did that.
Indeed. However, my uncertainty relating to my place as it is currently set up is that there is a single 3-phase meter, and that could well be taken to indicate that it was a single 'installation'. I imagine that I could ask to have it changed to three separate single-phase meters, but I suspect that the supplier would then not only regard it as three single-phase "installations" but also three "services", hence three Standing Charges!
Fair enough. I thought you were suggesting that I could avoid those issues (other than by claiming that I had 3 single-phase installations) by having "type-tested CUs" (i.e. invoking the 'conditional short-circuit test). As I said, if my installation does not qualify me to 'enjoy' 530.3.4, I don't think that would be the case.
If I recall correctly, the measured PFC is currently around 0.75kA.If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
