Three phase, split phase, or single phase when no rotating machines why three phase?

[ebee]

There surely nothing about a non-type-tested D that says that it can't include a 'main switch' / incomer ?

Indeed what was otherwise a ('type tested') CU, with a Main Switch, could cease to be a "CU" just because it contained one 'non-approved' device.

In any event, domestic installations ('under the control of ordinary persons') with more than one CU (which is far from uncommon) should (per BS7671) have a 'separate' Main Switch / isolator ("single point of isolation).

Kind Regards, John

agreed john

 

[ericmark]

One needs to measure the loop impedance to have more then 6kA simple ohms law, 230/6000 = 0.04 Ω (0.07 phase to phase) unlikely with a domestic supply, only once have I had that problem, used a 60 amp fuse, and the resistance of the fuse resulted in under 6 kA.

When selecting MCB/RCBO/RCD we are told we should measure both line - earth and line - neutral.

The Robin tester I was auto measured line - neutral for PSCC and line - earth for ELI, but when I got a Siemens tester, it only measured line - earth with the supplied three pin test lead. So I know I made an error with my testing until I realised.

I do find the Approved documents do seem to embellish on the actual law, and the reverse, found with the Landlord English regulations the law was actually more strict than the approved document.

But go to the HSE site and there are so many bits, one simply can't read them all. Also working out what is a recommendation and what is the law is hard.

When court cases have been published often details missing, be it trading standards over an EICR, or HSE over death due to metal in wall becoming live, we often are surprised at the results, to the extent of thinking there by grace of god go I.

Personally I think the old Wylex fuse box was well made and with a RCD feeding them I had them in my house for years, with fuses swapped for MCB's. But think the DNO had fitted a 100 amp fuse, so technically should not use the old Wylex box as main switch only rated 60 amp. But that is being pedantic like saying should not have a 6 amp MCB for lights as the ceiling rose acts as a junction box and is only rated at 5 amp. OK I can see why a 10 or 16 amp MCB should not be used on lights, but what's one extra amp?

I would not worry about fitting a three phase distribution board in my house, but one I am not classed as an ordinary person, and two not until a court case is fought do we really know what the courts would rule.

 

[EFLImpudence]

I do find the Approved documents do seem to embellish on the actual law,

Why do you read them?

 

[JohnW2]

One needs to measure the loop impedance to have more then 6kA simple ohms law, 230/6000 = 0.04 Ω (0.07 phase to phase) unlikely with a domestic supply,

We've been through this a good few times before.

I certainly agree that it is virtually inconceivable that the PSCC in a domestic installation will ever be anything even approaching 6kA.

The issue (in terms of BS7671) seems to arrise because of it's Ap[pendix 14, which says:#

..... In domestic (household) or similar premises, where a consumer unit to BS EN 61439-3 is used and the maximum
prospective fault current declared by the distributor is 16 kA, it is not necessary to measure or calculate prospective
fault current at the origin of the supply.

Even though it makes little/no sense in relation to domestic installations, It appears that DNOs generally do "declare the PFC" as being 16kA, which at least some people take to mean that one has to work with that figure. If one has that belief, then it means that, without the dispensation regarding type-tested CUs in 536.4.201, domestic DBs.CUs would have to use 16 kA devices.

If I recall, this discussion initially arose because someone (I think BAS!) suggested that, even though my installtion is 'under the control of an ordinary person' (myself), and even though all my DBs are ('type-tested') CUs, I could not invoke the dispensation of 536.4.201 to have only 6 kA devices, because my supply was not "a 230 V single-phase supply rated up to 100 A" (it is a 3-phase supply) - such that all my devices should be 16 kA ones!

I do find the Approved documents do seem to embellish on the actual law,

The do not claim or intend to be presenting the law. Rather, they are guidance as to one way of satisfying the law.

.... I would not worry about fitting a three phase distribution board in my house, but one I am not classed as an ordinary person, and two not until a court case is fought do we really know what the courts would rule.

The courts can only rule on the basis of laws and, despite your speculation, I personally very much doubt that there is any legislation that prevents the installation of a single-phase non-type-tested DB or a 3-phase DB in an installation which is 'under the control of an ordinary person'.

Kind Regards, John