16mm T&E for external building

[JohnW2]

So if i throw up a little stud partition with a door everything should be fine?

I believe so, strictly speaking (per the regs). Whether that partition and door would make it appreciably safer to have 'nearby sockets' (which, theoretically, could then be just outside that door) is perhaps more debatable.

Its 31sqm to give you an idea of size.

As I said, it's linear dimensions, not floor area, which matter - in a room with a shower (or bath) you are not allowed sockets within 3m of that shower (or bath).

Kind Regards, John

 

[RF Lighting]

Yes, it will be clipped to the wall again about 3m above ground level.

Twin & earth is not really suitable for that use.

No reason not to use SWA.

apart from cost... t&e in conduit is half the price.

You will not fit 16mm² t&e in conduit.

Also as this is going to be a shower room, is there a metallic water pipe entering the building?

Have you considered if you're going to extend the equipotential zone from the house, or if you'll make the outhouse into it's own zone with a local earth and bonding?

 

[influx]

Yes, it will be clipped to the wall again about 3m above ground level.

Twin & earth is not really suitable for that use.

No reason not to use SWA.

apart from cost... t&e in conduit is half the price.

You will not fit 16mm² t&e in conduit.

Also as this is going to be a shower room, is there a metallic water pipe entering the building?

Have you considered if you're going to extend the equipotential zone from the house, or if you'll make the outhouse into it's own zone with a local earth and bonding?

I was planning to use all plastic if possible, but as for equipotential zones i'll leave that to the professionals. I know my earthing goes back to the provider as there was a fault with it on the nearby pole last winter that caused all my lights to flicker.

will 16mm T&E not fit in 25mm conduit? 40mm starts to get a bit pricey.

 

[EFLImpudence]

You don't need 16mm².

 

[JohnW2]

You don't need 16mm².

True. I think the main question is the one which has been asked about bonding and equipotential zones. If there are things that need bonding in the outhouse (there's obviously going to be a water supply, but it might enter in plastic), there are clearly decisions to be made about the earthing arrangements, and if the house's equipotential zone were being 'exported', then the CPCs of either 10mm² or 16mm² would clearly be inadequate (I'm not sure, without looking it up, about SWA). That is clearly why the OP needs an electrician on board.

Kind Regards, John

 

[RF Lighting]

Yes that's exactly the point I was getting at. You don't want to spend money running a submains cable to find you then need to run a separate bonding conductor, which could end up costing more money than just putting in the right cable to start with.

 

[EFLImpudence]

True. I think the main question is the one which has been asked about bonding and equipotential zones.

The OP said his friend told him 16 would be needed and I don't think anyone has queried it.
It should be discussed with the electrician.

If there are things that need bonding in the outhouse (there's obviously going to be a water supply, but it might enter in plastic), there are clearly decisions to be made about the earthing arrangements,

It would be easier to install a section of plastic pipe.

and if the house's equipotential zone were all beingt 'exported',

Extended
If the pipe comes from the house ???

then the CPCs of either 10mm² or 16mm² would clearly be inadequate (I'm not sure, without looking it up, about SWA).

Have I missed something?
Why would such CPCs be required?

That is clearly why the OP needs an electrician on board.

He does.

 

[JohnW2]

The OP said his friend told him 16 would be needed and I don't think anyone has queried it. t should be discussed with the electrician.

Agreed - that's why I wrote "True" and also wrote that the OP required input from an electrician

If there are things that need bonding in the outhouse (there's obviously going to be a water supply, but it might enter in plastic), there are clearly decisions to be made about the earthing arrangements,

It would be easier to install a section of plastic pipe.

IF a metal water pipe were the only extraneous-c-p, then I agree.

and if the house's equipotential zone were all beingt 'exported',

Extended If the pipe comes from the house ???

Unless it's very old, I seriously doubt that the bulk of the (assumed underground) run of water pipe would be metal - although the bits emerging from the ground at the ends might be. That's how the water supply to my greenhouse works - nearly all plastic, but two or three feet of copper (partially underground) at each end.

then the CPCs of either 10mm² or 16mm² would clearly be inadequate (I'm not sure, without looking it up, about SWA).

Have I missed something? Why would such CPCs be required?

IF (on electrician's advice) the house's 'earth' were 'exported' to the outhouse, and if there were extraneous-c-ps in the outhouse, then there would be a need for a bonding conductor back to the house's MET. I was saying that no T+E has an adequate CPC to serve such a purpose.

Kind Regards, John

 

[influx]

The OP said his friend told him 16 would be needed and I don't think anyone has queried it. t should be discussed with the electrician.

Agreed - that's why I wrote "True" and also wrote that the OP required input from an electrician

If there are things that need bonding in the outhouse (there's obviously going to be a water supply, but it might enter in plastic), there are clearly decisions to be made about the earthing arrangements,

It would be easier to install a section of plastic pipe.

IF a metal water pipe were the only extraneous-c-p, then I agree.

and if the house's equipotential zone were all beingt 'exported',

Extended If the pipe comes from the house ???

Unless it's very old, I seriously doubt that the bulk of the (assumed underground) run of water pipe would be metal - although the bits emerging from the ground at the ends might be. That's how the water supply to my greenhouse works - nearly all plastic, but two or three feet of copper (partially underground) at each end.

then the CPCs of either 10mm² or 16mm² would clearly be inadequate (I'm not sure, without looking it up, about SWA).

Have I missed something? Why would such CPCs be required?

IF (on electrician's advice) the house's 'earth' were 'exported' to the outhouse, and if there were extraneous-c-ps in the outhouse, then there would be a need for a bonding conductor back to the house's MET. I was saying that no T+E has an adequate CPC to serve such a purpose.

Kind Regards, John

I was quoting 16mm based on the amp draw of a shower and kettle over a 25m run. I assume 10mm will be too thin for this?
The underground water pipe is all plastic. I think it was all renewed in the 80's.
Someone also mentioned that i could use a earth spike for a ground? Is this practice still done?

 

[JohnW2]

I was quoting 16mm based on the amp draw of a shower and kettle over a 25m run. I assume 10mm will be too thin for this?

You're probably not going to have the kettle and shower operating at the same time (both are usually on on very occasionally, for a few minutes) and, even if you did, a 7.5kW shower plus a 3kW kettle only amounts to around 45A, and 10mm² cable would probably be OK for that. Having said that, I generally advise people to try to 'future proof' supplies to outhouses by using cable larger than they actually need.

The underground water pipe is all plastic. I think it was all renewed in the 80's.

If no metal water pipe which has been in contact with the ground enters the outhouse, that makes things a bit easier. Are there any other metal things (other pipes, structural metal etc.) which enter the outhouse and are also in contact with the ground?

Someone also mentioned that i could use a earth spike for a ground? Is this practice still done?

As has been said, there are various options for the earthing arrangements at an outhouse, and a local 'earth spike' is one of those options. As has been said, this is one of the most important issues for you to discuss with your electrician.

Kind Regards, John

 

[westie101]

Sometimes I do end up wondering about the differences.

So T&E is unsuitable for outside use for a number of reasons
PVC
Non armoured
for just two

I suggest that some of you go and look at DNO mural wiring that is clipped to properties all over the country.
In the main it is PVC/PVC 16mm or 25mm meter tails. No different to what you guys use all the time, no special design PVC, and of course no steel surrounding it.
I suppose the difference is that it might be fused at 200 or 315A so must be safer in that use!!
But hey we've got thousands of kilometers of it and don't worry. So why is PVC seen as such a problem in a domestic situation.

Some odd dual standards here

The earlier type with a brown outer was no different, and then before that it was rubber with a fabric outer.

Similarly with split concentric, the outer earth is just that, connected to earth. The neutral is also connected to earth by the DNO system
So why does it need to be surrounded by steel earth?

ESQCR requires the outer earthed metal and accepts that all our cable with either stranded copper, a separate neutral/earth or a solid aluminum outer all comply (in fact modern HV cables just have stranded copper or solid aluminum)
But of course they are fused/electrically protected at much higher amperage!

Seems the installation trade really needs to modernise it's thinking

 

[EFLImpudence]

I was quoting 16mm based on the amp draw of a shower and kettle over a 25m run. I assume 10mm will be too thin for this?

A 7.5kW shower and 2kW kettle is, @240V, 39.6A therefore your 40A supply would be adequate for which a 6mm² cable would be sufficient and the volt drop acceptable even accounting for the shower.

However, if larger bonding conductors are required then you may as well install a larger cable.

The underground water pipe is all plastic. I think it was all renewed in the 80's.

Then that is not an issue.
Are there any other extraneous-conductive-parts?
That is metal parts emerging from the ground.

Someone also mentioned that i could use a earth spike for a ground? Is this practice still done?

This is only necessary to avoid expensive cabling arrangements.

 

[JohnW2]

So T&E is unsuitable for outside use for a number of reasons ... PVC, Non armoured, for just two ... I suggest that some of you go and look at DNO mural wiring that is clipped to properties all over the country. ... In the main it is PVC/PVC 16mm or 25mm meter tails. No different to what you guys use all the time, no special design PVC, and of course no steel surrounding it.

Like many others, I've had outdoor exposed PVC/PVC T+E in service for very many years (decades) in my time without any problem.

The one issue you don't mention is UV light. You say that DNOs do not use 'special PVC', but is it not more UV resistant than standard white or grey sheathed T+E? 'Ordinary' PVC T+E can certainly get pretty brittle with long-term UV exposure, but that is rarely an issue if it is well secured and not disturbed.

Kind Regards, John

 

[westie101]

You say that DNOs do not use 'special PVC', but is it not more UV resistant than standard white or grey sheathed T+E? 'Ordinary' PVC

Nope it is exactly the same with the same product code on the drums as standard "meter tail" PVC

 

[westie101]

Looking at the main issue here I'd run it in PVC trunking