Supply to OUTBUILDINGS

[acat]

Hi Folks

Please post all your ideas and suggestions here so we only have one place to look


Thanks


Chris

 

[sirocco]

I think the best way to describe it would be to give an example as each installation will have different requirements.

Lets say you want to supply a brick shed, 5 metres from the house/CU, with a lighting radial and a socket radial.

If no Extraneous Conductive Parts:

You could sellect a 4mm, two-core, SWA cable and use the armour as your CPC/Earth.

You could sellect a 4mm, three-core, SWA cable and use the third core as your CPC/Earth.

Either of these should be appropriate to feed your outbuilding, protected at the house CU by a 32A MCB.

At the outbuilding you would likely have a 30mA RCD main switch and a 6A and 20A MCB respectively.

If there were Extraneous Conductive Parts in the shed:

This changes things completely.

The installation now requires that the extraneous conductive part/s are bonded to the MET (This can be via an 'Earth Marshalling Terminal' - basically a 'remote' MET - as shown in the diagram in post 15)

The bonding of these 'Extraneous Conductive Parts' follows similar rules to the bonding carried out in the house/main installation, so the armour/third core probably wouldn't do.

You would probably be looking at minimum 10mm bonding conductor, so you either run 10mm SWA 3- Core - or you run a seperate bonding conductor alongside your SWA.

The good news is you just connect this conductor to the Earth Bar (EMT) in your garage CU, and use it as a combined CPC/Bonding.

You then run any final circuit CPCs and bonding conductors from this EMT.

That's about as good as I can explain it.

As I said earlier, each installation is different so you have to decide what is best.

E.G. If the outbuilding was 50 metres from the house, you might decide it's easier to rod it.
It's your decision at the end of the day

Thanks Wayne,
Great response, its getting clearer all the time.
Couple of further queries
The water supply to my outbuilding is 32mm Polyethylene Blue pipe fed directly from a street main with my house tee'd off it also in polyethene.
The only metal connections to this pipe in the outbuilding is a tap screwed to a plastic sink and a toilet cistern.
The drainage is similarly plastic connected to the street sewer.
Does the fact that, although the supply pipe is clearly non conductive, water flows in it make it in anyway an extraneous conductive part?
There are no metal gas/oil or water supply pipes coming into the outbuilding ,only plastic.
Also does the diagram at Post 15 hold good for both TNS and TNCS sytems?
Thanks for your help
Graham

 

[pushrod]

Does the fact that, although the supply pipe is clearly non conductive, water flows in it make it in anyway an extraneous conductive part?

Graham

Not an extraneous conductive part

 

[Hundleton1]

Got a question on this, looked at a job today, needs a shed at top of garden on supply, was going to run 3 core SWA up to it via the garden wall however the problem is i cant get the supply back to the CU, its a terraces house and the board rite at the front, i would have to rip the house in half to get a cable to it, there is just no way to get there with out them moving out.

the best option is off the utility room ring main as thats where the back door is, the main CU is split load twin RCD


whats the best way of doing this as its really classed as a spur ?

i was going to put a new CU in the shed with 6 and 16A MCB for lights and sockets with a another one in the utility room with the 20A, however the regs state that a fused spur must be limited to a rating of 13A

i was also not going to fit a RCD as per the RCD in series i keep reading about

 

[jase]

feeding off main house C.U would also be dependent on size of the submain to outbuilding too right? say if using a 16mm 3 core swa would be hard to terminate the earth and neutral in the C.U s so best option would be to split tails into fused switch, earth the swa banjo into an MET and then at outbuilding C.U bring in the 16 mm swa tails and earth with a rod and 10mm? earth

 

[Deleted member 9648]

Got a question on this, looked at a job today, needs a shed at top of garden on supply, was going to run 3 core SWA up to it via the garden wall however the problem is i cant get the supply back to the CU, its a terraces house and the board rite at the front, i would have to rip the house in half to get a cable to it, there is just no way to get there with out them moving out.

the best option is off the utility room ring main as thats where the back door is, the main CU is split load twin RCD


whats the best way of doing this as its really classed as a spur ?

i was going to put a new CU in the shed with 6 and 16A MCB for lights and sockets with a another one in the utility room with the 20A, however the regs state that a fused spur must be limited to a rating of 13A

i was also not going to fit a RCD as per the RCD in series i keep reading about

How much load is going to be used in the shed?....I would of thought a 13a FCU would cover most sheds.

 

[pushrod]

whats the best way of doing this as its really classed as a spur ?

i was going to put a new CU in the shed with 6 and 16A MCB for lights and sockets with a another one in the utility room with the 20A, however the regs state that a fused spur must be limited to a rating of 13A

i was also not going to fit a RCD as per the RCD in series i keep reading about

run it to a 13A metal clad FCU in the shed and wire it in either1.5mm T&E clipped direct, or 1.5mm singles in plastic conduit. Can't really see the point in a submain, just alot of expense.

 

[sirocco]

Waye,
Again, great post
Would the layout shown the diagram hold good for a TN-S system as well as PME?
Graham

Hi again,

I don't think many people have got a copy of 'Guidance Note 8', so I though I'd post this scanned picture from it.

Quite informative, I thought.

The sizes given are much higher than you'd see in a domestic - but the principal is the same, just scale it down.

It shows the two options for additional buildings using a TN-C-S supply. Building B3 is using the existing earth system and Building B2 is using a rod.

You'll notice that the combined CPC and Protective Bonding Conductor running to building B3 is 35mm, as are the bonding conductors in B3, even though the Line and Neutral conductors feeding B3 are only 25mm - this is because their selection is based on the supply neutral (120mm), and not the neutral feeding B3 itself (25mm).
This wouldn't matter to a domestic, as the size of protective bonding conductor remains at 10mm for a supply neutral up to 35mm

The regs quoted are the 16th reg numbers, as the IEE haven't thought it necessary to update GN8 to the 17th yet - I think a lot of the info didn't change.

This was the 2nd best £25.00 I've ever spent, by the way, so if anyone is thinking of buying it - go right ahead.

I'll probably post some more info from it when I get a minute Hope it helps.

 

[jase]

Waye,
Again, great post
Would the layout shown the diagram hold good for a TN-S system as well as PME?
Graham

what about if the main house was a TT?

 

[burt]

A definitive answer to this question (without it being immediately corrected) would be really nice. Do we rod the outbuilding and separate the earthing system from the house when supplying an outbuilding?

 

[telectrix]

A definitive answer to this question (without it being immediately corrected) would be really nice. Do we rod the outbuilding and separate the earthing system from the house when supplying an outbuilding?

read post#2 and others that explain it clearly.

 

[Deleted member 9648]

A definitive answer to this question (without it being immediately corrected) would be really nice. Do we rod the outbuilding and separate the earthing system from the house when supplying an outbuilding?

Definately maybe or not at all.

 

[Joe V.]

Although I think Pushrod may misunderstand the definition of 'extraneuos' (I also misunderstood the exact definition before someone on this forum corrected me), I agree with him on his point about earthing pipework. If I saw a house with a copper heating system, which had been electrically dissconected from the boiler by a short section of plastic pipe, I would want the remaining copper pipework to be bonded.
There are far too many ways a pipe (and all the radiators and taps connected to it)could become live. I should think that there are enough sparks who have seen live unearthed metalwork to agree

It may not be covered by the regs, but it's good practice at the very least.

This reminds me of a house where the CH radiators/pipework repeatedly attracted lighting strikes through the wall (breeze block & timber frame). Does / how does the presence of a lightning protection system on the outbuilding influence the choice of local rod or extending Earth from the main building ?

 

[GMES]

The thread is 3 years old so time to close it.