What kind of incoming electrical connections are these?

[newconnection]

If the existing supply is capable of supporting a 100A single-phase service, which you would have to ascertain from the supplier/DNO. If you needed 100A but the current supply cable is only good for 80A, then you would probably be better off opting for 3-phase on this existing supply rather than having the DNO install a new 100A single-phase supply. Any time you get involved with the DNO running in a new service cable, it will become expensive very quickly. A 3-phase board or three single-phase units would almost certainly be cheaper than having the DNO run a new cable.

Thanks - this makes sense.

 

[PBC_1966]

What are the advantages/disadvantages of a 3-phase versus 3 single phases?

Unless you are planning on having things like large machinery, massive kilns, or similar devices, there is almost nothing you will use domestically which actually runs as 3-phase. It's used for things like large motors in industrial situations because it's more efficient.

All of your normal domestic loads are single phase. If you had a 3-phase supply, you wouldn't be using it for 3-phase as such, simply distributing your single-phase loads across the three different phases. With, for example, a 60A 3-phase supply you can draw a maximum of 60A from each phase. So a 60A 3-phase supply would actually give you more available power than a 100A single-phase supply, so long as you are able to distribute the loads reasonably evenly between the phases (e.g. one electric shower on phase 1, another electric shower on phase 2, electric cooker on phase 3 and so on). Hence why I said that if the current supply cable will not support 100A, you would likely be better off adopting a 3-phase supply of lower rating rather than paying to have the DNO run a new 100A single-phase service.

 

[flameport]

If you do have the 3p supply installed, have a proper 3p distribution board fitted.
Any 'electrician' who suggests 3 separate consumer units should be shown the door.

 

[ban-all-sheds]

There is (almost) nothing for which you can use a 3-phase supply in a domestic installation in the UK.

You could potentially use one for some continental-make cookers, but you don't need to. The only thing I can think of actually in a house would be a high-powered instant water heater. Or if you wanted a lift or escalator.

If you're a keen woodworker or car mechanic, for example, you might find a 3-phase supply useful for professional machinery, a vehicle lift etc.

 

[ban-all-sheds]

If you do have the 3p supply installed, have a proper 3p distribution board fitted.
Any 'electrician' who suggests 3 separate consumer units should be shown the door.

Depends on the layout.

I can't quite picture it, but isn't this going to be subdivided into flats? Sharing the phases out between them might be the obvious thing to do, as would 1 SP CU per flat.

Also, from memory, when JohnW2 described his installation it seemed eminently sensible, and not something which could be improved by coalescing the CUs into a 3P one.

 

[newconnection]

If you do have the 3p supply installed, have a proper 3p distribution board fitted.
Any 'electrician' who suggests 3 separate consumer units should be shown the door.

Depends on the layout.

I can't quite picture it, but isn't this going to be subdivided into flats? Sharing the phases out between them might be the obvious thing to do, as would 1 SP CU per flat.

Also, from memory, when JohnW2 described his installation it seemed eminently sensible, and not something which could be improved by coalescing the CUs into a 3P one.

No, this will be a large house.

 

[newconnection]

Thanks for all the replies so far - an education to say the least and has helped to know the basics before getting a professional in.

Based on the assumption it is a 3 phase and IF it is, it seems the best way to go would be distributing the single-phase loads across the three different phases for which I will need a 3 phase meter from the electric supplier and a single 3 phase consumer board (3 separate single phase CUs is a bad idea?)

Anyone have any links to and decent 'metal' (latest regulation) 3 phase consumer boards, please?

 

[JohnW2]

Also, from memory, when JohnW2 described his installation it seemed eminently sensible, and not something which could be improved by coalescing the CUs into a 3P one.

Indeed so. Each of my three phases feeds a separate floor (plus a few complications for cellar, outhouses and garden!), each of which has its own local (single-phase) CU(s), the phases supplying 'distant' locations being fed via switch-fuses. I can't see what purpose a 3-phase DB would serve - apart from being a potential means of distribution to the remote floors (rather than the current Henleys + Switch fuses), it could only sensibly supply final circuits on the ground floor. It would surely be ludicrous for, say, second floor final circuits to originate in a ground floor DB, wouldn't it?

Kind Regards, John

 

[PBC_1966]

Each of my three phases feeds a separate floor (plus a few complications for cellar, outhouses and garden!), each of which has its own local (single-phase) CU(s), the phases supplying 'distant' locations being fed via switch-fuses.

Seems like a perfectly acceptable arrangement, given reasonable balancing of load across the system. And if I recall correctly from a couple of your photos, aren't your incoming phases still identified by the old red/blue/green scheme at your service?

 

[newconnection]

So 3 x single phase CUs or 1 x 3-phase CU?

 

[JohnW2]

Each of my three phases feeds a separate floor (plus a few complications for cellar, outhouses and garden!), each of which has its own local (single-phase) CU(s), the phases supplying 'distant' locations being fed via switch-fuses.

Seems like a perfectly acceptable arrangement, given reasonable balancing of load across the system.

Indeed - at least as reasonable than any other approach I can think of. Trying to introduce a 3-phase board would, IMO, merely be meddlesome (and unhelpful) for the sake of it! As in most houses, there is potential imbalance in that by far the greatest potential load is on the ground floor phase. However, I've partially addressed that by feeding the cellar, outhouses and E7 immersions from 'upper floor phases'.

And if I recall correctly from a couple of your photos, aren't your incoming phases still identified by the old red/blue/green scheme at your service?

Indeed so - at the fuses. On the input and output of the meter, they are identified as A, B & C - which is a new one on me ...

Untitled

• JohnW2
• 5 Apr 2012
• 3

(as always, note the {exposed} red insulation of the incoming neutral )

Kind Regards, John

 

[JohnW2]

So 3 x single phase CUs or 1 x 3-phase CU?

Yep, that's the choice, and if it's to be a single dwelling, in single occupancy, you'll just need a singe 3-phase meter to cover the whole lot, whichever way you do it.

Kind Regards, John

 

[PBC_1966]

Indeed so - at the fuses. On the input and output of the meter, they are identified as A, B & C - which is a new one on me ...

And your A/B/C labels don't follow the original red/blue/green phase sequence as identified on the board (when the colors changed, it wasn't a case of white replacing green, but of white replacing blue and blue taking the place of green - messing around with the colors isn't a new thing!). Maybe the phases were shuffled around at some point, or maybe the A/B/C labels are wrong.

A/B/C for phases is a common designation system over here.

 

[JohnW2]

And your A/B/C labels don't follow the original red/blue/green phase sequence as identified on the board ...

Indeed they don't - I forgot to mention that.

Maybe the phases were shuffled around at some point, or maybe the A/B/C labels are wrong. .... A/B/C for phases is a common designation system over here.

Fair enough - but, as a said, albeit my experience is very limited, A/B/C 'is a new one on me' over here! IIRC, that A/B/C labelling was added when I had the previous 3 single-phase meters changed to a single 3-phase one, soon after I acquired the installation, a little under 30 years ago - and has been perpetuated through a subsequent meter change.

Kind Regards, John

 

[newconnection]

So 3 x single phase CUs or 1 x 3-phase CU?

Yep, that's the choice

Apart from the 'neatness' of one CU, what are the advantages/disadvantages of either option?