Residential 3 Phase Supply to Single / 3 Phase

[JohnW2]

For single phase circuits it's not necessary to identify which phase is in use. Could be done if desired, black and grey sleeving is available. So are number and letter wire markers.

As you say, it certainly is not necessary, and I would be very surprised if (m)any people over-sleeved the brown of single-phase circuits with black or grey, even if all three phases were present in the installation as a whole.

However, whilst you say that the over-sleeving "could be done" (which, literally, is obviously true!), I wonder whether, strictly speaking, it would be compliant with BS7671, given that Table 51 indicates only brown as the colour which should be used to identify a line conductor in a single-phase AC circuit?

Kind Regards, John

 

[TimboTwo]

Why don't you ask your electrician about this?

 

[JohnW2]

I decided to go 3 phase for my incoming supply to allow for electric car charging etc and I am getting a 3 phase smart meter installed next week.

I agree with more-or-less everything that has been said to you about your proposed 3-phase board.

However, although it's presumably far too late for me to be asking, I can't help but wonder whether you actually need/needed a 3-phase supply. Do you actually have, or envisage that you will have, any 3-phase loads (you hint that you might be considering 3-phase EV charging, but nothing beyond that?).

Although, just to confuse things, my house is 'an exception which proves the rule' -) ), the vast majority of domestic properties in the UK (including those which have, or will have, EV charging) have single phase supplies - and the only usual reasons for wanting a 3-phase supply would be if one had loads which required such a supply, or if the total demand was too great for a standard (usually 100A maximum) single-phase supply (which would be unusual for a "2.5 floor" property).

For what it's worth, my large house ("4+ storey" - 3 floors + full-size cellar + attic) has (but doesn't really need!) a 3-phase supply and I've arranged that in one of the ways suggested above - with multiple single-phase CUs/DBs scattered around the house, spread over the phases on roughly a 'one per floor' basis, which offers some advantages. If I had, or ever come to have, any equipment which requires a 3-phase supply, it would be very simple to add a small further, 3-phase, DB to service the required circuit(s).

Kind Regards, John

 

[JohnW2]

Why don't you ask your electrician about this?

Indeed. Given the number and nature of the questions he's asked here, he is clearly going to have to do that.

Kind Regards, John

 

[winston1]

Neutral overload protection shuts off the supply, rather than disconnect the Neutral, I don't recall it being needed for the average install

OK. Makes sense.

 

[sparkypenguin]

Thanks very much for all the input , I'll try and respond to all questions in a logical order....

Why don't you ask your electrician about this?

I will but I always like to have multiple opinions about any aspect of my build and to learn about what's possible etc, after all it's very rare that there is only one solution and it does allow me to have a more meaningful conversation!

I agree with more-or-less everything that has been said to you about your proposed 3-phase board.

However, although it's presumably far too late for me to be asking, I can't help but wonder whether you actually need/needed a 3-phase supply. Do you actually have, or envisage that you will have, any 3-phase loads (you hint that you might be considering 3-phase EV charging, but nothing beyond that?).

Although, just to confuse things, my house is 'an exception which proves the rule' -) ), the vast majority of domestic properties in the UK (including those which have, or will have, EV charging) have single phase supplies - and the only usual reasons for wanting a 3-phase supply would be if one had loads which required such a supply, or if the total demand was too great for a standard (usually 100A maximum) single-phase supply (which would be unusual for a "2.5 floor" property).

For what it's worth, my large house ("4+ storey" - 3 floors + full-size cellar + attic) has (but doesn't really need!) a 3-phase supply and I've arranged that in one of the ways suggested above - with multiple single-phase CUs/DBs scattered around the house, spread over the phases on roughly a 'one per floor' basis, which offers some advantages. If I had, or ever come to have, any equipment which requires a 3-phase supply, it would be very simple to add a small further, 3-phase, DB to service the required circuit(s).

Kind Regards, John

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.
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. 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.

Thats just an standard TPN board you have shown, The size you pick depends on how many cirucits, obviously a 12Way board will give you 12 TPN ways, or 36(3x12) SP ways, or any combination in between.Normal to leav at least 20% spare ways.
You'll need RCBOs on most if not all of you SPN circuits, TPN cirucits may or may not need RCD protection, TP rcbos are an rare/unusual thing, so if you needed RCD protetcion to a three phase circuit, then stick a service centre on the top or bottom of the board and run the cirucit through 4 pole RCD in there. Or design so that you dont need an RCD at the board end.

You'd of course want the incommer as well, thats a rookie mistake to make to order board without the incommer!
Who is in charge of designing/installing the installation, because it sounds like you want to order a board without really understanding what you actually need.......

I thought that a standard board was what I needed?
I understand about the number of ways so 12 way or maybe slightly larger.
I'll look for a board with incomer and thanks for promoting me to "rookie" level .
I only just started looking into the design of the system yesterday morning and not planning to order the board yet, I just wanted to get an idea of what was possible / allowed etc so I can discuss with my electrician and also to allow me to consider any implications on other aspects of the build.

Thanks for clarifying

Does it matter if the 3 phases are balanced?
I have read that it does not really matter as it's just like having 3 different houses one on each phase, however I have also read that it could lead to a high and dangerous neutral current?
If I was drawing the full 18KW on one phase and nothing on the others would this matter?
Do I need to fit some form of Neutral overload protection?

This is a copy of my last post and I have received 2 responses.....

er no. If the neutral was disconnected by a breaker or fuse the line voltages could drift all over the place up to 415 volts.

and

Neutral overload protection shuts off the supply, rather than disconnect the Neutral, I dont recall it being needed for the average install

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?
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.
And although it may not be "needed" for an average install I would rather fit some form of protection if the only downside is the extra cost?


As I have stated I only have a basic knowledge of electrics and I did only start to look into this yesterday morning. I have taken a photo of the incoming supply which may help?
20210918_171405.jpg
20210918_171409.jpg
20210918_171412.jpg

Thanks again for all the continued help

 

[Risteard]

Thats just an standard TPN board you have shown, The size you pick depends on how many cirucits, obviously a 12Way board will give you 12 TPN ways, or 36(3x12) SP ways, or any combination in between.Normal to leav at least 20% spare ways.
You'll need RCBOs on most if not all of you SPN circuits, TPN cirucits may or may not need RCD protection, TP rcbos are an rare/unusual thing, so if you needed RCD protetcion to a three phase circuit, then stick a service centre on the top or bottom of the board and run the cirucit through 4 pole RCD in there. Or design so that you dont need an RCD at the board end.

You'd of course want the incommer as well, thats a rookie mistake to make to order board without the incommer!

Who is in charge of designing/installing the installation, because it sounds like you want to order a board without really understanding what you actually need.......

The EVSE will need to be wired through a 4 pole RCCB, as it must interrupt all live conductors.

 

[Risteard]

As you say, it certainly is not necessary, and I would be very surprised if (m)any people over-sleeved the brown of single-phase circuits with black or grey, even if all three phases were present in the installation as a whole.

However, whilst you say that the over-sleeving "could be done" (which, literally, is obviously true!), I wonder whether, strictly speaking, it would be compliant with BS7671, given that Table 51 indicates only brown as the colour which should be used to identify a line conductor in a single-phase AC circuit?

Kind Regards, John

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

 

[flameport]

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.

18kW is approximately 78 amps.

With 78 amps on one phase and nothing on the other two, the neutral current is 78 amps.
With all 3 phases at 78 amps, the neutral current is zero.
The only circumstances where the neutral current can exceed that of one phase is where harmonics are present. The solution there is to remove the harmonics, not install spurious overload devices.
You don't need neutral overcurrent protection.

Phases should be balanced, and by installing a standard 3 phase board they will be. However nothing will happen if they are not balanced, or if for some reason al the loads in use at a particular time were on one phase.

the incoming supply

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

 

[Adam_151]

I thought that a standard board was what I needed?

It is IMHO, I was just a little unsure why the modified picture was shown as if to illustrate something that you thought was unusual

I'll look for a board with incomer and thanks for promoting me to "rookie" level

You mis-understand generally all commercial boards come without incommer, you order the incommer you need as a separate item, as opposed most domestic boards where the incommer is supplied as standard, thats why its a rookie mistake to forgot to add the incommer, it was a half tongue in cheek comment when you copied the description of a board without incommer as asked "Is this what I need?" It certainly wouldn't be the first time I've seen someone who does mostly domestic work have to take a second trip back to the wholesaler!

 

[SUNRAY]

This is a copy of my last post and I have received 2 responses.....

er no. If the neutral was disconnected by a breaker or fuse the line voltages could drift all over the place up to 415 volts.

and

Neutral overload protection shuts off the supply, rather than disconnect the Neutral, I dont recall it being needed for the average install

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?

Thanks again for all the continued help

It's OK to ignore winstons reply as he doesn't know what he's talking about as demonstrated in his reply to Rockys correct post

OK. Makes sense.

 

[winston1]

It's OK to ignore winstons reply as he doesn't know what he's talking about as demonstrated in his reply to Rockys correct post

It is very rude to tell people to ignore other members replies. Especially when I DO know what I am talking about. FACT if the neutral is disconnected the phase voltage could rise to 415 volts. Rocky’s explanation of course was also correct.

 

[Risteard]

It is very rude to tell people to ignore other members replies. Especially when I DO know what I am talking about. FACT if the neutral is disconnected the phase voltage could rise to 415 volts. Rocky’s explanation of course was also correct.

The harmonised voltage is 400V.

 

[SUNRAY]

It is very rude to tell people to ignore other members replies. Especially when I DO know what I am talking about. FACT if the neutral is disconnected the phase voltage could rise to 415 volts. Rocky’s explanation of course was also correct.

It's also very rude to post uninformative and, in this case, incorrect advice. OP even pointed out there was contradiction between the two posts and then you verified your error by posting

OK. Makes sense.

As to your latest... FACT... (yes I can shout too)...

FACT if the neutral is disconnected the phase voltage could rise to 415 volts.

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?

 

[333rocky333]

OK. Makes sense.

Neutral monitoring i recall is more used when the Neutral conductor size is reduced compared with the phase conductors, i would guess its more used in Network distribution supplies.
you are correct to say it would be foolish too somehow break just the Neutral conductor.