Supply to OUTBUILDINGS

[acat]

Hi Folks

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


Thanks


Chris

 

[WayneL]

I'll start it off, then.

Contrary to some popular urban myths, there is no requirement for a seperate earthing system (e.g. TT/Earth Rod) at the outbuilding, regardless of the earthing system of the main installation.

The only thing that needs to be taken into consideration is the presence of extraneous conductive parts in the outbuilding and, if required, the CSA of the' Protective Bonding Conductor' that will need to be run along with the supply to the outbuilding.

The option is there to install an earth rod, should this be an easier and more cost effective option.
You then need to seperate your outbuilding earthing system from the main installation earthing system.
The feed to the outbuilding would be earthed at the supply end only.

That should get things rolling

 

[Mr.Black]

As the cable(buried) is supplying a special installation the supply cable therefore should be RCD protected.

If the supply cable is visible for its entire length does it still need RCD protection?

Anyone agree

 

[WayneL]

As the cable(buried) is supplying a special installation the supply cable therefore should be RCD protected.

If the supply cable is visible for its entire length does it still need RCD protection?

Anyone agree

I would have to disagree, Mr Black, no requirement for RCD protection of the cable if mechanically protected. (e.g. SWA), unless an RCD was required for earth fault protection to meet EFLI maximums.

 

[Mr.Black]

What about it being a special installation?

 

[Deleted member 9648]

Bs 7671....the BRB section 7, lists special locations. A normal garden outbuilding is not a special location. Where such outbuildings come under special locations such as construction sites,swimming pools etc there are additional requirements and it is important to refer to the BRB for more information.

 

[Sav]

Superb post and really helpful !! I am writing down my notes as we gom along !!
Keep up the good work and any other such subjects or ideas others may have, would be great to put them on, so that we ( really meaning me ) , can write down helpful notes and links etc.

Best regards and have a great weekend everybody,

Sav

 

[SirKit Breaker]

I would have to disagree, Mr Black, no requirement for RCD protection of the cable if mechanically protected. (e.g. SWA), unless an RCD was required for earth fault protection to meet EFLI maximums.

I agree and I always try to split supply with a Henley block and switch fuse to out buildings, just so any problems with it doesnt affect the house. The supply to your house doesnt have RCD protection and its basically the same set up.

 

[Jason Smith]

On a subject like this full of Grey areas, we need to define what 7671 says, as thats the law. After that, we need to find out what our individual governing bodies state.Best practices etc. As its for those reasons that opinions differ so greatly. So if we can define what we say by quoting a reg, or say I do this, etc, because I believe its best practice etc, that would help.
I personally have followed my" master" and will rod the lot if I get a chance to prevent transporting a fault. It is time to move on from that as I have learnt from this forum, to develop my own methods.

 

[Jason Smith]

I'll start it off, then.

Contrary to some popular urban myths, there is no requirement for a seperate earthing system (e.g. TT/Earth Rod) at the outbuilding, regardless of the earthing system of the main installation.

The only thing that needs to be taken into consideration is the presence of extraneous conductive parts in the outbuilding and, if required, the CSA of the' Protective Bonding Conductor' that will need to be run along with the supply to the outbuilding.

The option is there to install an earth rod, should this be an easier and more cost effective option.
You then need to seperate your outbuilding earthing system from the main installation earthing system.
The feed to the outbuilding would be earthed at the supply end only.

That should get things rolling

Wayne, sounds a brilliant explanation and I bet it couldnt be put into fewer words.watching this thread closely.

 

[Mr.Black]

I know the outhouse isn't a Special Location it comes under SPECIAL INSTALLATION there is a difference!!!!!!!!!!!!!!!!!!!!!

Check in the PART P DOCUMENT.Then tell me what you think.

 

[Jason Smith]

Right then, a special installation, in this context, is a outdoor power installation, and is therfore covered by Part P.(leckys guide to the building regs,green book, page 71). Therfore, its to be treated as a dwelling,additional info within this page give advice on outside sockets etc, so I cant see it effects anytechnical decisions . Do you agree

 

[Mr.Black]

If you mean that the supply cable should be protected by an RCD then absolutey my good man.Very important as some spark may come along at a later date and decide the outhouse needs a earth spike,fires it into the ground and ouch ouch what happened there..

 

[Jason Smith]

If you mean that the supply cable should be protected by an RCD then absolutey my good man.Very important as some spark may come along at a later date and decide the outhouse needs a earth spike,fires it into the ground and ouch ouch what happened there..

WOT - I take it you infer that a sparky would do such a thing as to drive an earth rod through a cable ? never, surely ?

 

[WayneL]

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.

 

[Deleted member 9648]

I know the outhouse isn't a Special Location it comes under SPECIAL INSTALLATION there is a difference!!!!!!!!!!!!!!!!!!!!!

Check in the PART P DOCUMENT.Then tell me what you think.

Not sure what the relevance of this is. Part P is about what work is notifiable.....Bs 7671 determines how that work is carried out,not part P. In Bs 7671 a garden outbuilding is not a special location and therefore only the general requirements of Bs 7671 apply.

 

[Jason Smith]

Not sure what the relevance of this is. Part P is about what work is notifiable.....Bs 7671 determines how that work is carried out,not part P. In Bs 7671 a garden outbuilding is not a special location and therefore only the general requirements of Bs 7671 apply.

Right, thats what I am saying, BS 7671 applies to a dwelling as well as an outbuilding. If an outbuiding is obviously part of a dwelling, then 7671 and part P applies, so wheather or not its a special location or Installation, its still 7671. so we can set aside the fact that its either a special installation or location, as it has no bearing on the technical aspects. Whats next.

 

[pushrod]

I was asking a lecturer today about this today - he teaches the 17th wiring regs (and really knows his stuff) and it was his opinion that any shed/outbuilding outside the main building's equipotential zone should have its own earthing system, ie an earth rod.
The swa doesn't need an rcd because it has mechanical protection.
Earth the swa at the supply only. There must be an rcd at the outbuilding

I did ask about extending the house's equipotential zone to include the outbuilding ... but didn't really get the chance to explore that question.

 

[martysparky]

Hi again,


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

Good call nice one

 

[WayneL]

I was asking a lecturer today about this today - he teaches the 17th wiring regs (and really knows his stuff) and it was his opinion that any shed/outbuilding outside the main building's equipotential zone should have its own earthing system, ie an earth rod.

Hi mate,

You should get him to have a read of GN8 then mate, coz he's got it wrong

I'm not criticising him, by the way, a lot of people have got this idea that you have to TT an outbuilding, but it's all rumour.
There may be some circumstances where it would make more sense to TT it, but that's a judgement call by the sparky on the job.

The other thing worth mentioning is that, if there are no extraneous conductive parts in the outbuilding, and therefore no bonding requirements, then you can simply run your SWA supply to the outbuilding, utilising either the armour, or a third core, as the CPC - once again, regardless of the type of earthing system of the main installation.