Residential 3 Phase Supply to Single / 3 Phase

[JohnW2]

They shouldn't be sleeved, as single phase circuits are required to be identified by brown for the phase (line).

That's what I suggested.

 

[JohnW2]

Reasons for going 3 phase.. I personally don't believe that 18KW is enough for a modern new build given that more stuff is going to go electrical, and although I do have a gas supply to the property, I am not planning to install any gas components. I may wish to install a 22KW EV, my solar panels are potentially going to be a 10KW 3 phase system, my air source heat pump is potentially going to be a 3 phase model, I will also have an electric oven / hob and 1 electric shower. Plus it did not cost much more to go 3 phase so I could not see any downside.

Fair enough. I agree that there is no appreciable downside, other than the initial complexity (and cost) of the installation. However, I suppose my point was that the vast majority of domestic installations in the UK have (and 'manage with', even if they have EV charging) a single-phase supply (potentially 23kW with a 100A supply) and that will undoubtedly remain the case for at least a very long time to come.
However, if you are seriously contemplating a 22kW EV charging (something that virtually no domestic properties would consider, or be able to have), a single-phase supply would obviously not be adequate.

As for splitting the supply to single phase DB's over the floors this is not something I even considered. I did start off planning to use separate DB's but just assumed they all had to be close to the meter and therefore all in the garage and 90% of the top floors cabling is already in place.

On the contrary, the main point/advantage in doing as I do is that most of the CUs/DBs are very remote from the meter - probably at least 20 metres 'as the cable flies' in the case of my top floor. As well as facilitating easy isolation of just sections of the installation, it means that the 'distribution circuits' (from meter to CU/DB) can be in large cable (mine are mainly 25mm²), thereby appreciably reducing the loop impedance and voltage drop in the more remote (i.e. top floor) parts of the house. I've never bothered to do the sums, but it may well not have been possible to use the usual size cables for final circuits on the top floor if they had all been wired all the way back to a CU/DB a long way away.

Plus I only just found out yesterday morning that I could use a 3 phase DB and simply take single phases from it and hence I am thinking I may as well use a 3 phase board to give more flexibility going forward.

If, as you indicate, you have, or may have, a need for some 3-phase circuits, then that is certainly a reasonable way to go - although, as I said, there's no reasonn why you could not have had a separate, fairly small, DB for 3-phase circuits even if most of the installation used single-phase DB(ds).

Kind Regards, John

 

[JohnW2]

... They appear to contradict each other as one assumes only the neutral will be shut off and the other states that the entire supply will be shut off?

AS has been said, the former would be dangerous, and would never be done. As has also been said, the latter (with excessive neutral current resulting in all four conductors being disconnected) would not be required in dopmestic (or most other) installations.

And if anyone can shed any light onto whether my 3 phases need to be balanced and whether 18KW on one phase whilst zero on the other 2 could potentially cause a dangerous neutral current.

I think flameport has answered your question. As he has said, in the absence of harmonics (very unlikley to be an appreciable issue for you), the neutral current can never be greater than the greatest of the line current in the three phases - so if the neutral and line conductors are all the same size, there would be no reason to worry about the neutral current, even if only one of the three phases had any load at all.

Kind Regards, John

 

[winston1]

The harmonised voltage is 400V.

So what. The actual voltage is usually over 415v. Over 415v is more dangerous than 400v.

 

[winston1]

It's also very rude to post uninformative and, in this case, incorrect advice.

I didn't. This what I posted.

FACT if the neutral is disconnected the phase voltage could rise to 415 volts. Rocky’s explanation of course was also correct.

Hmmm I'd rather expect phase voltage to be a nominal 400V all the time and 415V is well within the current standards. What is your point?

You know as well as I do that the usual UK mainland voltage is around 415v not 400v and can in fact rise to 440v or 10% above so called nominal.

 

[winston1]

You are correct to say it would be foolish to somehow break just the neutral conductor.

Thankyou Rocky. Good to have someone agree with me rather than squabbling and ruining threads for the sake of it

 

[BS3036]

so called nominal.

- don't know what to say!

 

[JohnW2]

- don't know what to say!

It's interesting how careless omission of a hyphen can make a big difference

Kind Regards, John

 

[sparkypenguin]

Thanks again to everyone for their input, it's very much appreciated.
I hopefully now have attained a very basic "rookie" (Adam_151 ) knowledge of what I need to discuss with my electrician.
Even including understanding how the comments by winston1 and 333rocky333, that I originally thought were contradictory, were not as they appear to be both true.

A couple more questions...

Install a foundation earth electrode while you still have the opportunity.

Given that their is an earth connection in the meter box do I still need to / should I do this?

Surprising that they actually installed a 3 phase cutout in a small SP meter box.
Hopefully it will be small meter.

I have tried to find out the size of the meter but they have said that they cannot confirm which make / model until they fit it.
They have however stated that if required they will fit on the other side of the box on my internal garage wall.
Does this sound acceptable?

Mark.

 

[SUNRAY]

.

 

[flameport]

I've already had most of the cables installed and they all terminate in the garage

Too late for a foundation earth, as it goes in the foundation of the building.

Does this sound acceptable?

No. It's just making do with what's there.
Cabinet should have been sized for a 3 phase supply.

Is there actually an electrician involved with this build?

 

[JohnW2]

Given that their is an earth connection in the meter box do I still need to / should I do this?

No, you don't. As you say, your supply comes with a 'PME' ("TN-C-S") earth, and that's all you need. Flameport's previous comment related to the fact that your diagrams showed an 'earth rod' (labelled "Ground Rod", suggesting that it was created by an American) , rather than a supplier-provided earth.

I have tried to find out the size of the meter but they have said that they cannot confirm which make / model until they fit it. ... They have however stated that if required they will fit on the other side of the box on my internal garage wall. Does this sound acceptable?

Flameport has replied that it is 'not acceptable' and, whilst probably not ideal, that's just his opinion - there's nothing electrically wrong with it, and they wouldn't do it if t was not electrically acceptable. Traditionally, the only real practical downside of not having the meter accessible from outside the property would have been that 'meter readers' would have had to gain access to your garage to read the meter - but since it is a smart meter, that's not an issue.

Kind Regards, John

 

[sparkypenguin]

.

Good point!

Too late for a foundation earth, as it goes in the foundation of the building.
No. It's just making do with what's there.
Cabinet should have been sized for a 3 phase supply.
Is there actually an electrician involved with this build?

Apologies but the OP diagram I uploaded was completely incorrect as my system is actual as John states in his most recent post, PME TN-C-S, therefore no earth rod required.
With hindsight I would have installed the correct meter box but I only decided to go 3 phase after the meter box etc was fitted but I did discuss in length with Northern Power Grid as to whether they could use the existing box and they were fine with it but they did say it may result in the supplier having to fit the meter internally.
I have informed the supplier, EON, that it may have to be fitted in the garage and I have also sent them meter box photos along with the measurements of the available space but they have not yet confirmed what they will be doing.
There was an electrician but I have sacked him as I have decided to do the work myself!

No, you don't. As you say, your supply comes with a 'PME' ("TN-C-S") earth, and that's all you need. Flameport's previous comment related to the fact that your diagrams showed an 'earth rod' (labelled "Ground Rod", suggesting that it was created by an American) , rather than a supplier-provided earth.
Flameport has replied that it is 'not acceptable' and, whilst probably not ideal, that's just his opinion - there's nothing electrically wrong with it, and they wouldn't do it if t was not electrically acceptable. Traditionally, the only real practical downside of not having the meter accessible from outside the property would have been that 'meter readers' would have had to gain access to your garage to read the meter - but since it is a smart meter, that's not an issue.

Kind Regards, John

Thanks for confirming and as I replied to flameport I now understand that my first post was completely wrong and I can see why I would have needed an earth rod in that scenario.
I can however confirm that my system does come with a PME TN-C-S earth so as you stated no earth rod required.
Good to know that the meter in the garage, although probably not ideal, is not a no no.

Well I think that's all the info I need so once again thanks to everyone who has contributed

 

[SUNRAY]

.

Good point!

Ah, somehow I managed to post a reply to a completely different thread here

 

[JohnW2]

Ah, somehow I managed to post a reply to a completely different thread here

You're certainly not the first to have done that - and equally certainly won't be the last

Kind Regards, John