3 Phase to single phase

[Adam_151]

If you are going to be charging off it (as opposed to it being only for information, i.e. 'used xxx kwh for lighting, and yyy kwh for small power) the it needs to be a MID approved meter

 

[morg]

Thanks for all the posts and information, interesting reading!
I will get more information about current setup and will report back on the questions asked.

Only suggested single phase installation, as it appears to be alot cheaper, for example 3 phase meter is over £130, where as single phase meter is £30.
Everything 3 phase related seems double/triple the cost, as stated I don't intend on using any 3 phase equipment.

I have looked at one of these Wylex 100amp CU with RCD (£50), I think it would look good in a small workshop looks somewhat commercial.
But would go for whatever setup is cost effective!

If you are going to be charging off it (as opposed to it being only for information, i.e. 'used xxx kwh for lighting, and yyy kwh for small power) the it needs to be a MID approved meter

No no it won't be for charging purposes, its just a 'check meter' for information as you suggest.

 

[JohnW2]

Possible but not something that is desirable, necessary or to be recommended. ... If you only want a few circuits, a 2 or 4 way 3 phase board would be a far better option, those would provide up to 6 or 12 single phase circuits and still retain the possibility of one or more 3 phase circuits as well for the inevitable day when some new piece of 3 phase equipment arrives. ... For metering, a meter is installed. A 3 phase one in the supply to your new board.

If I understand correctly, I presume that there already is a 3-phase board (probably more than 4-way), supplying 3-phase circuits for the other users and single-phase circuit(s) for the OP.

However, what you propose (which, as above, is probably the present situation) would presumably not, in itself, address the OP's need - to separately monitor/meter the total consumption of his single-phase circuits(s). If, as was quite probably your thinking (and, again, may well already be the case) his single-phase circuits are spread across phases, that would become tedious, because he presumably would then have to separately monitor/meter each of his single-phase circuits (and add up the figures) (or perhaps use a 3-pahse 'check meter' if he has only three single-phase circuits on different phases).

Kind Regards, John

 

[flameport]

for example 3 phase meter is over £130

Some are.
Others are not.
https://meters.co.uk/products/mx300-100/

 

[JohnW2]

Some are. Others are not. https://meters.co.uk/products/mx300-100/

I suppose so ...

...Genuine retro meter from the 80’s. Were built to last.

I suppose I probably would not argue with that

Kind Regards, John

 

[SUNRAY]

Some are.
Others are not.
https://meters.co.uk/products/mx300-100/

That's a no brainer, even if a single phase CU is fitted on only one phase it's semi future proofed.

 

[flameport]

because he presumably would then have to separately monitor/meter each of his single-phase circuits (and add up the figures) (or perhaps use a 3-pahse 'check meter' if he has only three single-phase circuits on different phases).

Existing 3 phase supply -> 5 core cable -> 3 phase meter -> 5 core cable -> new 3 phase board which can have a selection of single or 3 phase circuits connected.

Meter registers total energy used for the new board regardless of what circuits are in it.

As I said previously - this is a very simple, everyday installation. It's just a sub board with it's own meter. Thousands of similar installations in commercial premises everywhere.

 

[JohnW2]

Existing 3 phase supply -> 5 core cable -> 3 phase meter -> 5 core cable -> new 3 phase board which can have a selection of single or 3 phase circuits connected. Meter registers total energy used for the new board regardless of what circuits are in it. ... It's just a sub board with it's own meter.

Indeed. I misunderstood, and thought you were suggesting that the entire installation (including the OP's single-phase circuits) should be fed from a single 3-phase board (which is why I said that was probably what they already had).

In that case, if I now understand you correctly, the only difference between your proposal and the OP's is that he proposed a 3-core (L,N,E) feed from one of the three phases feeding (via a single-phase meter) a single-phase sub board containing single phase MCBs for his single-phase circuits, whereas you are propose a 5-core feed (via a 3-phase meter) to a 3-phase sub board which (currently) would contain single-phase MCBs for his single phase circuits. Is that correct?

If so, I agree that your suggestion would represent theoretical 'future-proofing' but if the OP is certain that he will never need any 3-phase circuits, it presumably would not offer any advantage? Whilst nothing is impossible, if he currently estimates his 'maximum machinery load as 2-3kW, it would seem that he is probably right in saying that he is never likely to need 3-phase loads.

Kind Regards, John

 

[ericmark]

I have over the years been told a consumer unit is a type tested distribution unit with a maximum of 100 amp single phase for use in premises in the control of an ordinary person. However I have never found the base rule, it may be HSE or building regulations, there is

530.3.4 For an installation with a 230 V single-phase supply rated up to 100A that is under the control of ordinary persons. Switchgear and controlgear assemblies shall either comply with BS EN 60439-3 and Regulation 432.1 or be a consumer unit 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.

but it does not actually say three phase can't under the control of an ordinary person maybe some one can clarify what control an ordinary person is permitted.

I remember when a neighbour died the widow had to find some one with a licence to take his guns, could it be similar in our houses? when we die our widows have to engage an electrician to be in control? I seem to remember a few companies where an electrical firm was on some sort of retainer or contract to look after the installation, but I have never looked into it.

 

[JohnW2]

I have over the years been told a consumer unit is a type tested distribution unit with a maximum of 100 amp single phase for use in premises in the control of an ordinary person.

The BS7671 definition of a Consumer Unit does not say much of that - only that it is 'type tested and that it must have a DP main switch. The rest of what you say comes, as you illustrate, from the situation in which use of a Consumer Unit allows one to avoid what is effectively a requirement for 16kA devices, per 536.4.201 of BS7671:2018 (your 530.3.4 from BS7671:2008).

It really seems a bit daft (inexplicable) to me that the required breaking capacity of protective devices can change according to whether the person 'in control' of the DB is, or is not, 'an ordinary person'!

... but it does not actually say three phase can't under the control of an ordinary person maybe some one can clarify what control an ordinary person is permitted.

I think you're probably making this more complicated than it is. The bit of 536.4.201 (530.3.4 in 17th) you quote is merely a dispensation/relaxation saying that IF it is a "230 V single-phase supply rated up to 100A that is under the control of ordinary persons.", then use of a type-tested CU allows one to use devices with a lower breaking capacity. In all other cases, including that of a 3-phase supply (and regardless of who is 'in control' of it), the primary part of that reg applies, namely:

The relevant fault current (short-circuit) rating of the assembly should be equal to or exceed the maximum prospective fault current at the point of connection to the system.

Nothing in that reg (nor anything else in BS7671 of which I am aware) says anything about who may, or may not, be 'in control of' a 3-phase supply.

In this context, I am an 'ordinary person', and am presumably deemed to be 'in control of' the 3-phase (3 x 80A) supply to my house, and I can't see how that can be contrary to any regulations! The reality is that the three phases are treated totally separately so, applying common sense (and despite some arguments we've had here!), I am perfectly comfortable with having 6kA devices in type-tested CUs in each of those three phases, and doubt that it contravening any regulations.

Kind Regards, John