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Hi,

UKPN are installing a new 200A 3PN supply. Their incoming cable is 95mm.
As per the Multiple Occupancy Building recommendation G87 they will only supply the cut out. I now need to supply an isolator and Ryefield (or equivalent).


Looking at table 4D1A 70mm cable will cover me for free air spaced, using rule of thumb I'm thinking 35mm main bonding. But looking at table 54.8 looks like 25mm is fine, did I read this correct?
544.1.1 We do also have PME.

Here's the snag, in my area we only have 2 phases in the street, so you have to over spec the Ryefield by 33% to get your required number of ways. i.e. 9 ways only has 6 usable ways when only using 2 phases.
Normally not a big deal, but I'm tight for space as this is a retro fit.
So here is my thought, is there any reason why I can't bring in L1 and L2 into the Ryefield, then link L2 to L3 in the Ryefield to enable me to use spare ways? To be clear L3 does not exist so I am not joining phases.
My thought is as long as I do not overload cutout there is no problem. UKPN protect their cable with 200A fuse and cutout bus bar is rated at 200A, so I don't see a problem. But am I missing something?

Thanks
Michael
 
Your tails won't be spaced in free air will they!

Why do you think 35mm main bonding will be adequate? I came up with 50mm off the top of my head (next standard size larger than 47.5)
But you would need to confirm with ukpn if they require larger for any reason.

How can it be a 3PN supply of there are only two phases? Is it a two phase supply or two phases of a three phase supply?

You'd be better off getting the distribution board custom made for two phases, otherwise you will not be balancing your loads across the phases.
 
Tails will be in electric intake cupboard, 1M max from UKPN cutout into my isolator, then another 1M max from isolator into Distribution board, maybe a clip or 2, this is free air right?

UKPN won't comment on anything upstream from their cutout. EDF have just advised needs to be 35mm as per network calculations, not BS7671.

It is only 2 phases in the street.

Since posting I've spoken to Lucy Electrical. They have confirmed okay to link L2 with spare L3. But I agree I'll need to balance phases.

EDF have also advised you can use any TP&N distribution board as long as you can lock it off as they no longer do this, it is the BNO's responsibility.
 
I agree with the 50.0 for main bonding but ask the supplier the size of the PEN conductor. If you are going to alter the Ryfield for operation with two phases you will need either the manufacturer to undertake this or obtain a specific kit from them but it is not likely one exists. Anything you do with the board would void any warranties.
 
Tails will be in electric intake cupboard, 1M max from UKPN cutout into my isolator, then another 1M max from isolator into Distribution board, maybe a clip or 2, this is free air right?

UKPN won't comment on anything upstream from their cutout. EDF have just advised needs to be 35mm as per network calculations, not BS7671.

It is only 2 phases in the street.

Since posting I've spoken to Lucy Electrical. They have confirmed okay to link L2 with spare L3. But I agree I'll need to balance phases.

EDF have also advised you can use any TP&N distribution board as long as you can lock it off as they no longer do this, it is the BNO's responsibility.

A clip or two? Yeeeeeehaw! Do the job properly with galv trunking and the main switch and DB directly coupled on to it.

What else do you need to know from ukpn about the upstream installation?
EDF are presumably the meter operator? In which case their advice won't count for anything if you have failed to comply with BS7671.
The suppliers PEN conductor from your OP is 95mm therefore 35mm bonding is incorrect.

Yes, but what are those two phases? A two phase supply or two phases of a three phase supply? Do you know the difference?

You are right it doesn't have to be manufactured by ryefield, it could be any DB fitted with hrc fuses.
 
I agree trunking would be the preffered route, but this is a retrofit, so this might not be an option, but I'm not ruling it out until I have completed the design. Space is the biggest hurdle.
I'm gonna need to be careful with cable bends, I recall there is a calculation for the minimum radius but I can't find it, does anyone know of a link?

BS7671 table 54.8 advised 25mm Main protective bonding. UKPN have advised I should use 25mm. EDF state 35mm, but I will ask for a copy of "Network Regulations" which he referred to.

Yes, EDF are DNO
I asked UKPN to comment on [FONT=&#10]Multiple occupancydistribution board[/FONT], just looking for ideas.

EDF commented you can use any appropriately rated distribution board as long as you can lock it off. MCCB or fused. Albeit having costed this, the Lucy MSDB wins in both cost and it's designed specifically for the job.

I must admit I do not know if it is actually 2 phases or using 2 phases from a 3 phase supply. I will seek clarification. I made an assumption it was the later as I am not aware of 2 phase and no I do not know the difference. I would be grateful for a quick explanation.
 
I agree trunking would be the preffered route, but this is a retrofit, so this might not be an option, but I'm not ruling it out until I have completed the design. Space is the biggest hurdle.
I'm gonna need to be careful with cable bends, I recall there is a calculation for the minimum radius but I can't find it, does anyone know of a link?

BS7671 table 54.8 advised 25mm Main protective bonding. UKPN have advised I should use 25mm. EDF state 35mm, but I will ask for a copy of "Network Regulations" which he referred to.

Yes, EDF are DNO
I asked UKPN to comment on [FONT=&#10]Multiple occupancydistribution board[/FONT], just looking for ideas.

EDF commented you can use any appropriately rated distribution board as long as you can lock it off. MCCB or fused. Albeit having costed this, the Lucy MSDB wins in both cost and it's designed specifically for the job.

I must admit I do not know if it is actually 2 phases or using 2 phases from a 3 phase supply. I will seek clarification. I made an assumption it was the later as I am not aware of 2 phase and no I do not know the difference. I would be grateful for a quick explanation.

Being a retrofit does not remove the need to provide good protection to the tails. If bend radius is a problem then why don't you use a cable with a smaller bend radius? What cable are you planning to use for this anyway?

Which area is this in? I thought EDF were no longer a DNO in the United Kingdom!

My mistake on the main bond, it does appear to be 35mm

Oh dear, you might want to learn a little bit about the basic supply systems!
Two phase supplies are fed via a transformer which has a 480V centre tapped output, with the centre tap referenced to earth to make it a neutral point. This you have two phases at 240V wrt earth and 480V between them.
Two phases of a three phase supply is just what it says on the tin.

Whereabouts in the country is this? There are a few areas which still have some bizarre supply arrangements due to using the old DC supply cables from the 1930's
 
Yes, EDF are DNO
I asked UKPN to comment on [FONT=&#10]Multiple occupancydistribution board[/FONT], just looking for ideas.

EDF commented you can use any appropriately rated distribution board as long as you can lock it off. MCCB or fused. Albeit having costed this, the Lucy MSDB wins in both cost and it's designed specifically for the job..

EDF are not a DNO in the UK any more, I've just checked the list.

Earlier you said it could be any distribution board, now you are limiting it to mccb or fuse protected dbs, make your mind up!


Sent from my iPad using Tapatalk
 
Sorry EDF are Meter Operator
UKPN are DNO; it's Hastings, South East England.

I should have added etc..... after "Any Distribution board"

My tails need to be 70mm,

Where are you getting figure of 35mm for bonding?

Thanks for 2 phase explanation, I also had a quick google, just not aware of it until now.
 
Sorry EDF are Meter Operator
UKPN are DNO; it's Hastings, South East England.

I should have added etc..... after "Any Distribution board"

My tails need to be 70mm,

Where are you getting figure of 35mm for bonding?

Thanks for 2 phase explanation, I also had a quick google, just not aware of it until now.

The supply neutral is 95mm according to your OP.
Up to 95mm is 25mm bond
95mm and above is 35mm
So in my understanding of the English language 'up to 95mm' does not include 95mm but stops just short of it.
 
No,
BS7671 Table 54.8
Over 50mm up to 95mm - 25mm
Over 95mm up to 150mm - 35mm

Therefore 95mm is 25mm

Also, BS7671 544.1.1 Except where PME conditions apply, a main protective bonding conductor shall have a cross-sectional area not less than half the cross-sectional area required for the earthling conductor of the insulation and not less than 6mm. The cross-sectional area need not exceed 25mm...........

I read this again as 25mm, do you agree?

Appreciate your comments, but neither of us probably at our best this late :)
 
No,
BS7671 Table 54.8
Over 50mm up to 95mm - 25mm
Over 95mm up to 150mm - 35mm

Therefore 95mm is 25mm

Also, BS7671 544.1.1 Except where PME conditions apply, a main protective bonding conductor shall have a cross-sectional area not less than half the cross-sectional area required for the earthling conductor of the insulation and not less than 6mm. The cross-sectional area need not exceed 25mm...........

I read this again as 25mm, do you agree?

Appreciate your comments, but neither of us probably at our best this late :)

544.1.1 is irrelevant as you have said its PME.

So yes it does look like 25mm may be acceptable
 
You can get single phase ryefield boards if you don't want to waste capacity and keep the board as designed just install two single phase ryefield boards.

If I was you I'd stick with a ryefield board if you can as the meter operators are often very difficult if you have anything installed out of the ordinary.
 

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