Electrical question: Incoming supply wires sub-standard for BS7671

[Evan Brown]

Hi everyone

I've had an electrician's report done as part of the moving documentation on a property that I just bought. The property is in Scotland, in case that makes a difference, and it is installed on Scottish and Southern Energy's network (Scottish Hydro Electric, as was.)

The electrician's report states that the incoming supply wires to the property are not compliant with BS7671. They are currently 10mm2 and should be 16mm2, as I understand it.

We want to do some upgrade work on the electrical system but will be running up against the maximum capacity of the incoming supply due to the size of these wires.

I contacted SSE and they have said that they will quote for the supply to be upgraded. My question is: should I have to pay for this? Isn't it the responsibility of the supplier to ensure that their network meets the required standards? The electrician that did the report said that he has never seen such small incoming supply wires to a property before.

Any advice would be much appreciated. The electrician mentioned that, if we do have to pay, there may be grants for this work available, but I can't see how we could be liable for the cost of the work here.

[Andrew Gabriel]

BS7671 doesn't cover "Suppliers Works", so there's no way for the incoming supply wires to conform to BS7671.

That's not to say they aren't too small, but it's up to the local network operator. Any idea what your main cutout rating is? If your voltage goes out of range, then you would have a good argument, but that's most unlikely.

[Tim Watts]

Evan Brown wibbled on Tuesday 10 August 2010 11:24

Is he talking about the meter tails from their meter to your fusebox (where BS7671 applies) or the main incomers *to* the suppliers cutout fuse - BS7671

*does not* apply to them - they have their own regulations. Incomers are not uncommonly a size down from what you'd think they ought to be, and what BS7671 would require you to have for your meter tails.

What is the size of the main fuse by the meter? (Sometimes there's a label on the side of the fuse carrier - at least a max rating, the fuse could be smaller)? Or you could ring the supplier and ask them what your supply is.

Are you on overhead wires or underground feed? In a town or the middle of nowhere? If you're in the middle of the countryside on overhead with random transformers up poles, there might be a limit on what they *can* give you without upgrading miles of cable.

Not necessarily. You can always apply for an upgrade but these days (since privatisation) I suspect (but not sure) that they could charge you a contributory amount even if the work is on their side.

I can believe it. One thing you haven't told us - what is your power budget, ie how many amps do you plan on using, max?

[Evan Brown]

He's actually recommended upgrading both the incomers and the meter tails. The meter tails are currently 14mm2 I think and he wants them to be 25mm2.

I'm not sure and I'm away from the property now so can't check easily. I will phone SSE to find out.

The incoming supply comes from an overhead pole but the electrician reckons that most of the run will be underground. Funnily enough the property is right next to a hydro electric power station!

The electrician told us that our supply will handle 200 amps maximum as it currently is. The previous owner of the house was an electrical engineer at the power station and he put sockets/lights everywhere. We have been told that with the upgrades we want to do, we will be pushing the total load capability of the current system.

Thanks for your reply.

[Andrew Gabriel]

Max single phase supply you can get is 100A (sometimes lower if the local network can't handle it).

If you want more than that, you normally have to take a 3-phase supply.

[Tim Watts]

16mm2 I think

100a is the max unless it is 3 phase .

I don't see how you could possinly need 200A unless you are heating a massive building electrically?

[Jim K]

sounds like you;re being sold something here... or you aren't telling the whole story?

WTF are you going to do with more than 200amps? frankenstein? make heavy water?

Jim K

[js.b1]

Up to the load-side of the meter terminals the DNO can do what they want. That is subject to ESQW regulations (no supply cable joints under driveways), but not subject to BS7671 and very often the DNO side will often not comply for cost reasons multipled across the network. For example supply cable will appear undersized, burial depth can be very shallow, meter supply-side tails can be 16mm even if a 100A fuse.

After the load-side of the meter terminals BS7671 does apply. Meter load-side tails are 16mm with a 60A or 80A fuse, 25mm with a

100A fuse - the sizing is as much re fault disconnect by the upstream fuse which is nearly always BS1361 (a few get BS88 main fuses).

Either you have a 2 phase supply or the electrician is talking spheres. Domestic is 1ph (40)-60-80-100A or 2ph or 3ph, which is still 100A per phase.

Immaterial: diversity applies to socket & light final circuits. Unless you have 10x 3.3kW storage heaters I do not see a problem.

I hope someone is not simply adding up the MCB ratings and saying you need a 3 phase 100A supply, that will only apply if you have a very large number of fixed loads where diversity does not apply. An example would be 2x 11kW showers and 10x 3.3kW storage heaters which would necessitate a multi-phase supply. Diversity applies, calculation in the On Site Guide and even that is a little severe because domestic can handle 2x 11kW showers on a 100A fuse (quite common on very large detached new-build houses).

What exactly do you want to connect to it?

Can you post a picture of your existing DNO cutout & meter & consumer unit? (Take a photo and host it on Flickr or any other free hosting website).

[Andy Wade]

Might be 7/0.064 inch, which is about 14 mm^2 and used to be the standard size [1] for household meter tails before metrication.

[1] With a 60 A main fuse.

[ARWadsworth]

Or maybe the tails between the cutout and the meter. I know some electricians will not change then in case the electricity police arrest them.

Cheers

Adam

[ARWadsworth]

Are you sure about that? I have moved lots of CUs for cutomers where they have had the main cut out moved and lots of the new joints were under the driveway.

[js.b1]

Actually no is not correct in the OPs context, apologies.

ESQW 2002 actually states jointing must be done with good mechanical protection and cites the example of robust plastic resin filled enclosure (boat).

However a NatGrid inspector did advise in January 2010 that he could not joint the neighbour's Loop-In supply if my cutout were used (under a driveway or not), and there was another limitation on jointing PILC also.

Gone to digout the docs if I can find them, I suspect they are NatGrid specific.

[js.b1]

It might come down to DNO "whim".

When I asked Scottish Power to move an originator loop-in supply cutout they refused to joint the neighbour's PILC under the driveway - they said it would require a New Supply laid to each house. That I could understand. However when I asked them to move the cutout to a different location which would merely require PILC extending they said they could not joint PILC under a driveway or path cited ESQW. However I can find nothing in ESQW to support that comment - indeed the contrary as you found re resin filled boats being specifically cited.

If that is a rule it works against them re cost. Neighbour some houses away had a 1947 PILC supply which was cut by a spare in 1972 and repaired. That repair failed just after the winter and they said they could not do a repair and laid new cable for him and to the neighbour via the same route under the original land easement. It could not be some environmental nonsen^^s^regulation about jointing lead covered cable and instead replacing could it?

I actually wonder how much comes down to outsourced contractors. Neighbours in the other direction all had new alkathene gas - those with patterned concrete driveway got the pipe run under the neighbour's driveway whilst they were out. No easement was obtained before the works were completed. I also know those contractors went bust before finishing perhaps deliberately :-)

The OP referring to 200A supply could be possible if the "house" was actually a former commercial property. Either that or there is a 125A Commando socket and cable running back to the plant... sort of taking work home with him.

[ARWadsworth]

It could do.

I have seen extensions where a loop in supply was allowed externally but the original cable to the neighbour was not allowed to run under the extension. Lots of digging:-)

Dunno. And all the lads that do the work are there just to do their job according to their spec sheet. One of them did say "now two specs are the same".

Well they buggered up my friends driveway.

Never seen bigger than 100A. Mind you, I wonder how many houses share the

600A fuse in the substation with my house?

[The Wanderer]

No they can't. They're governed by the The Electricity Safety, Quality and Continuity Regulations 2002.

[The Wanderer]

They're having you on. In this day and age, they will try to get you to pay for whatever they can. Just refer them to the The Electricity Safety, Quality and Continuity Regulations 2002, and ask them to confirm in writing that they consider your service arrangement meets the requirements of those regulations.

Hint: I used to work for Southern until shortly after it was privatised. The emphasis is strictly on the bottom line of the balance sheet......

[js.b1]

Actually I was about to correct that too, even ESQW comments:

ESQW 24. Equipment on a consumer's premises

24(1) Equipment... installed on consumers' premises must be suitable for its purpose and safe. Examples of such equipment include: cables, meters, distribution boards, isolators and switches. ... ... In order to demonstrate compliance with the requirements of regulation 24(1) duty holders should adopt the standards of construction and installation necessary to comply with BS7671Requirements for Electrical Installations.

Off to read ESQCR...

[js.b1]

Having read the ESQCR and amendments, a bit clearer.

That might yet stop EDF extending the supply cable by a bit of copper pipe under the armour with an EC clamp over the top of it. Newly installed street lights around a trade park have a similar arrangement (armour bent back over a piece of copper pipe over the sheath, then EC clamped) and have that delightful (not) cable-slap ringing as you walk by in the wind.

[js.b1]

NG "gas service" publish relatively clear policy, guidelines, price structure. DNO "electric service" do not have anything like the same clarity or even availability!

The neighbour with the cable fault and other loop-in neighbour got new individual cables, outside cabinets, all done by 1-man in a no-name white-van. Just a short outage whilst the changeover was made. It makes me wonder if it was outsourced, in which case there could well be different "rules" re liability v labour v materials. Split con costs little, a trench by NG is costed like space travel whereas a trench by 1-man contractor probably costs far less.

Quite a few houses do share the same fuse, the diversity is quite a lot. Cabinets used to be 1MVA whereas I think 2MVA is now used, like the old sub-station buildings stuff gets shrunk.

In semi-rural areas they just kept adding to the end of the pipe, probably not expecting electric showers. Around here the builders added houses every 25yrs (near enough) since 1900. So what was once the edge of the town got steadily bigger as the farmland vanished and the cables which predate 1950 just got more stuck on them. I know they had to "switch a tapping" about 20yrs ago because voltage could sag too low during peak load (and now runs 252-257V at no load). Everyone noted that whenever the DNO crowd come around they always seem to "run around and suck teeth" when they saw electric cookers & showers, "reminding" people they should have permission before adding any fixed load or they can disconnect it. Saying that to the proverbial baby- just-exploded-whilst-changing-the-nappy mother is sort of met by a "I will do the digging, you just die and fall into it" look and they realise any amount of physical labour is preferable :-)

I do recall when asked to quote for an u/g to 3ph supply for a kiln in

1985 (naively not realising what that would cost!) the DNO engineer said "it is in the street, but no way".

So I suspect they just stack more on the existing infrastructure. This is why when you want to expand a true rural supply they quote something hilarious because they want you to pay for "future neighbours" and it is conversely one way by not doing so that you can keep the developers away.