The old barn electrics

[La Poste]

Greetings all.

My neighbour has just had a garage built in the shape of an old barn.
We live in the sticks and I guess the only way the architect could get it through planning was to make it this way.
It's in keeping with the surrounding area.

As he is my next door neighbour he has asked me to do the electrics.
The supply is a 2.5mm SWA buried underground.
The system is a TN-S with the transformer on a pole in the field out back.

I will have a quick look at it later but I have a couple of small queries if anyone can enlighten me.

As the supply is SWA which means it is earthed in a metal housing does it need to be RCD protected.
I don't think it does, I am thinking of a distribution circuit you know like they supply street lights with and a 5 second disconnection time.
As the supply is TN-S from an underground supply cable I don't think exporting an earth from the main house will be a problem.
I could TT it and would probably get low results for EFLI but I would prefer to keep the distributors earth.
Can anyone see any problems with exporting a TN-S earth?

The other question is I want to encase all the cables in black galvanized metal conduit to give it a more pleasant look but I am little concerned about the sockets.
What would members consider to be the best and most attractive sockets and switches to put on.
They would be metal surface mounted supplied by cables in black enameled conduit.
Has anyone any recommendations?

I will take some pictures in due time but I wondered if anyone has ever done a job like this.

Many thanks.

 

[topquark]

No need for the dist circuit to be RCD protected, but you will want to earth the metal armour at the supply end.

As you're considering metal conduit I'd go for metal clad fittings, particularly in a garage. Less likely to be damaged.

When you check out the garage, see if there's any extraneous metal in the structure as that would need bonding back to the MET if you're using the suppliers earth. So that would mean running an larger bonding cable as well as the SWA (2.5mm would not be large enough for bonding I suspect).

 

[Engineer54]

Greetings all.

My neighbour has just had a garage built in the shape of an old barn.
We live in the sticks and I guess the only way the architect could get it through planning was to make it this way.
It's in keeping with the surrounding area.

As he is my next door neighbour he has asked me to do the electrics.
The supply is a 2.5mm SWA buried underground.
The system is a TN-S with the transformer on a pole in the field out back.

I will have a quick look at it later but I have a couple of small queries if anyone can enlighten me.

As the supply is SWA which means it is earthed in a metal housing does it need to be RCD protected.
I don't think it does, I am thinking of a distribution circuit you know like they supply street lights with and a 5 second disconnection time.
As the supply is TN-S from an underground supply cable I don't think exporting an earth from the main house will be a problem.
I could TT it and would probably get low results for EFLI but I would prefer to keep the distributors earth.
Can anyone see any problems with exporting a TN-S earth?

The other question is I want to encase all the cables in black galvanized metal conduit to give it a more pleasant look but I am little concerned about the sockets.
What would members consider to be the best and most attractive sockets and switches to put on.
They would be metal surface mounted supplied by cables in black enameled conduit.
Has anyone any recommendations?

I will take some pictures in due time but I wondered if anyone has ever done a job like this.

Many thanks.

A 2.5mm SWA is pointless waste of money, use a minimum 4mm 3 core SWA, at least you will be future proofing to some extent. 3 core, as then you can use the 3rd core as your bond and the armour as your CPC. In reality they will both be connected to the garage EMT !!anyway...

I personally wouldn't use black enamelled conduit in a garage, due to corrosion over the years. Nothing to stop you using Black PVC conduit, or indeed galvanised conduit, that will match the metal clad switches and socket outlets.
You have a choice to either use standard type metal-clad fitments or the full sized metal clad, where you can use standard metal switch and outlet fronts of your neighbors choice...

 

[topquark]

Must admit, mine's done in plastic conduit and just about to do another the same way (still with metal clad accessories). You may even find that 4mm isn't large enough for bonding but at least that'll take you up to around 40A possible supply (xlpe).

 

[topquark]

Here's some piccy's:

View attachment 8613View attachment 8614View attachment 8615View attachment 8616

 

[johnboy6083]

you tart!
personally id be tempted to run black 50x50plastic trunking round the top, with conduit drope. Will be very easy to do, and allows numerous additions ect, without any hassle.

 

[Dan23584]

you tart!
personally id be tempted to run black 50x50plastic trunking round the top, with conduit drope. Will be very easy to do, and allows numerous additions ect, without any hassle.

I used a similar method in a boiler house not long ago, not long after they wanted additions so I was glad for the trunking!

 

[johnboy6083]

I used a similar method in a boiler house not long ago, not long after they wanted additions so I was glad for the trunking!

i love trunking jobs, as its so easy to add and remove stuff. also looks very neat.

 

[Engineer54]

Nice conduit job!! Shows that you can make a decent job of PVC conduit when done right..

PS ...I like the artexed ceiling in your garage, ...different!! lol!!!

 

[EastAnglian]

If you have other services in the barn (water, structural metal) which require bonding then I would suggest you are best off making the installation TT by using an earth electrode (and RCD of course!) at the garage end. Else you will end up needing to confirm the minimum size of the bonding cable and may choose a larger size SWA than you actually need. If there is no local bonding required then simply export LNE in a 3 core armoured cable.

The size of the SWA should be determined by considering the maximum demand for the garage (now and in the forseeable future) and the length of the cable run to determine voltage drop. 2.5mm SWA may well be perfectly adequate if it can comfortable meet the above 2 requirements.

 

[La Poste]

Thanks guys really helpful, I like the pictures Topquark.

The supply is already there and is a 2.5 mm SWA although not sure if it has its own CPC or just the armoring.

There are no extraneous metallic parts introducing earth potential, just a concrete floor and an empty building although this may change.

I noticed a gas bond of 6mm attached to the gas pipe outside the main house which is very close to the barn.

Getting a new 6mm or 10mm bonding cable from the barn to the fuse board in the house would be impossible without digging the whole patio up so if he were to introduce a water supply I could attach a bond to the existing gas bond( not strictly correct as per regulations, needs to be an unbroken cable) or just TT the whole thing.

It looks like a nice job.

 

[EastAnglian]

If you don't have 3 cores in the SWA you could work out the CSA of the armour (use a micrometer to measure the diameter of one strand, apply Pi*r*r to get its CSA, then multiply by the number or strands). Then check this against Table 54.7 in the regs.

TT is probably easier!

 

[johnboy6083]

the flaw of the abve plan is that CSA of conductors is nominal. That means that the manufactureres will conduct tests to see how much current the conductor will take ect, and then assign a nominal CSA. if you look at different manufacturers of cable,the actual measured CSA will be different. it probably wont me much but there will be slight differences

 

[Engineer54]

If no extraneous metalwork in the garage, then just use what you have, the armouring of the SWA cable. Don't even consider TT'ing this garage there is really no need whatsoever!!


If your neighbour later wants to have a water supply in there, tell him to pipe it in, in Plastic pipe. lol!!!

 

[johnboy6083]

couldnt agree more. The garage is probably one of the most dangerous parts of a domsetic electrical installation, due to the use of power tools, the possible dam[p and wet environment, and the alomst certain use of gear outside the equipotential zone. with all of this considered, why would you consider using the least protected of all supplies (TT). RCD's can and do fail.

 

[EastAnglian]

Before we loose sight of the question don't forget that La Poste is working with a pre-installed cable and he will need to satisfy himself that the CPC meets the requirements of section 543 and table 54.1.

If its a 3 core SWA then job done - easy - but if not then it will be necessary to confirm that the CSA of the armour meets the Regulation.

If it does not then TT is the remaining option.

 

[topquark]

Nice conduit job!! Shows that you can make a decent job of PVC conduit when done right..

PS ...I like the artexed ceiling in your garage, ...different!! lol!!!

About 13 years old now, so done in the proper colour singles as well

 

[johnboy6083]

Before we loose sight of the question don't forget that La Poste is working with a pre-installed cable and he will need to satisfy himself that the CPC meets the requirements of section 543.

If its a 3 core SWA then job done - easy - but if not then it will be necessary to confirm that the CSA of the armour meets the Regulation.

If it does not then TT is the remaining option.

The SWA will be constructed to a british standard. This will list the available cables sizes, and the armour CSA, along with other information

 

[Engineer54]

Iv'e Never yet come across a SWA cable under 95mm2 where it's armouring doesn't meet the requirements of being used as the cables CPC.

In this instance the armouring needs to have a minimum CSA of 5.7mm, a standard 2 core SWA cable has a armouring CSA of 17mm. So I think that the SWA will JUST meet CPC requirements!! ...lol!! I think we can now all agree then that the SW Armouring will be just Fine!! lol!!

 

[La Poste]

If your neighbour later wants to have a water supply in there, tell him to pipe it in, in Plastic pipe. lol!!!

I should have thought of that straight away LOL.
There's nothing like missing the obvious to make me feel daft.

 

[yellowvanman]

Iv'e Never yet come across a SWA cable under 95mm2 where it's armouring doesn't meet the requirements of being used as the cables CPC.

In this instance the armouring needs to have a minimum CSA of 5.7mm, a standard 2 core SWA cable has a armouring CSA of 17mm. So I think that the SWA will JUST meet CPC requirements!! ...lol!! I think we can now all agree then that the SW Armouring will be just Fine!! lol!!

If I remember correctly the ECA were saying that SWA up to 400mm was sufficient for CPC requirements, although I think 240mm was borderline.

 

[telectrix]

check the thread "can we use the armour of SWA as cpc" there's a chart showing all sizes , and whether the armour is ok as CPC

 

[Engineer54]

check the thread "can we use the armour of SWA as cpc" there's a chart showing all sizes , and whether the armour is ok as CPC

There are 2 chart/tables in that thread, i tend to use the one Spin posted (i think on page 4 /post 37 or thereabouts), and have been using that table for quite a few years now without incident. I don't use the table Lenny posted, far too many calculations to have make on too many cable sizes etc, before getting definitive results.

To be honest, these day's i only look up such tables when my mind goes blank...lol!! As i'm using SWA cables for much of this and past projects distribution systems. So they are almost imprinted, in my mind, even the cables that i've had to calculate to prove compliance.. lol!!!

 

[La Poste]

Here's some pictures of the barn.

It's a garage really in the shape of a barn.

 

[Octopus]

So I guess the relevent question also is whether plumbing in a new "building" on the end of an existing SWA cable is notifiable under Part P?

For me I'm not sure you may get away with simply providing an EIC but others may have alternative opinions.