dnb

Current best practice for outside light cable routes

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I need to consider where the outside light cabling needs to go before I put the cladding on the house so that I can provision for it. So I wondered what the best practice for outside lights on a timber clad SIPS build is. There is little to no experience of SIPS here, not that I believe it should make too much difference.

 

Some of the discussions are around using "safe zones" (I know the 18th calls them something else now) and them not transfering through an outside wall, so for example a pair of lights at the side of an external door: The cable shouldn't just go through at the fitting location and then up the wall inside the house without being protected in some way (30mA RCD would seem to cover this) because there's nothing on the inside of at least one side to indicate the cable is there, but it's made a hole into a bit of "living space" into a prime coat hook location so even though it is protected, a better design would be for the cable to be elsewhere. Going up the outside of the SIPS to ceiling height and then into the house via the ventilation void of cladding solves this, but it seems a lot like using the cavity in a traditional build (the cable can of course be mechanically secured, so no risk of tracking water) so is frowned upon as a method. 

 

Going further, It would be good from a thermal view to collect the various outside lights to as few common cables as possible to minimise structure penetrations, but that's quite a lot of wiring on the SIPS behind the cladding.  I can see people getting even more upset about that! (Needless to say running anything on surface of the cladding in conduit is not acceptable to one person.)

 

Maybe I should put more carrots in the diet so we can all see in the dark? It might be easier. 😉 

Edited by dnb

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A very interested observer on this one.

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I was rather hoping it was going to end up a daft question and I was overthinking it in very specific ways while missing the fairly obvious (as is my usual practice 😉 )

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Cables should be 50mm from the surface 

Or protected by 30mA RCD and installed in a zone or have earthed armouring.

 

so run a swa cable if it’s difficult.

 

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Where is the light switch in relation to the outside lights?

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2 hours ago, dnb said:

The cable shouldn't just go through at the fitting location and then up the wall inside the house without being protected in some way (30mA RCD would seem to cover this) because there's nothing on the inside of at least one side to indicate the cable is there.

 

That is not strictly true, when looking at a wall, you are meant to consider both sides of the wall as their could be sockets etc. on the otherside too. 

 

I didn't build in SIPs but really that ought not to make a massive difference because you would not put cables in a TF behind the insulation either so bringing it through the wall inside is acceptable as long as you then continue on using an acceptable route - i.e. straight from location. What are you doing inside? Service void using battens then plasterboard?

 

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16 minutes ago, Carrerahill said:

when looking at a wall, you are meant to consider both sides of the wall as their could be sockets etc. on the otherside too

I thought this only applied to thin walls. But then reading a bit more there is a rule that you shouldn't back to back sockets in stud walls to stop fire spread. So I am more than happy to accept and rely on this argument. It should be obvious from looking through the door.

 

For what it's worth I am insisting on lining holes through the structure with conduit (and filling the end with intumescent sealant) so there can be no possibility of reaction with the insulation. 

 

16 minutes ago, Carrerahill said:

What are you doing inside? Service void using battens then plasterboard?

Yes. Exactly this. 25mm or 40mm depending on the services required in the area.

 

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1 hour ago, TonyT said:

Where is the light switch in relation to the outside lights?

There's the issue. The plan is for dmx controlled lighting. Does a low voltage computer interface type switch count as a switch for the purpose of safe zones? 

 

1 hour ago, TonyT said:

Cables should be 50mm from the surface 

Or protected by 30mA RCD and installed in a zone or have earthed armouring.

Are you sure the ands and ors are typed correctly here?  The wording implies I can do anything as long as it is NOT in a zone and within 50mm of the surface.

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I’m not in the office now, so unless someone has a copy to hand, I will take a photo of the text on Monday.

 

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6 minutes ago, TonyT said:

I’m not in the office now, so unless someone has a copy to hand, I will take a photo of the text on Monday

Don't worry. I can look it up myself. I have acquired a copy of the blue book from work.

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Home now, and have found the regulation I think we are talking about: 522.6.202

 

My understanding of it is:

 

A cable is in a wall at a depth less than 50mm shall be in a permitted zone as per the diagram @TonyT posted AND be protected by RCD.

 

Where the accessory (etc) is on the other side of the wall and can be determined as such the permitted zone extends to the other side if the wall is up to 100mm thick (so essentially single skin blocks and stud walls only) OR it must comply with reg 522.6.204. This is the case I find myself needing to use. And strangely the RCD requirement seems to now not apply, but I see no reason NOT to have one!!

 

Reg 522.6.2-4 gives 5 options for various earthed, mechanical and isolation protections, SWA looking like the easiest.

 

So my choice seems fairly clear - the wall is about 250mm thick, so clearly the permitted zone does not extend. I therefore need either steel conduit or SWA on the inside.

 

Incidentally, I can't find a reg that stops me putting conduit on the outer skin of the SIPS having had a read of "the book" for a couple of hours. I know we've already established it's not the done thing, but I would like to understand the reasoning.

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I think a 20 mm plastic conduit passed through the sip and sealed on the internal and external sheathing.

with the swa passing though the conduit also sealed.

1.0mm 3 core will go through the conduit.

it can be glanced  to the switch box/ controller to earth the armour and also use the 3rd core in the swa.  Then at the light end tape up the armour and utilise the 3 core only.

 

Edited by TonyT

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On 22/01/2021 at 12:53, dnb said:

Yes. Exactly this. 25mm or 40mm depending on the services required in the area.

 

You will be good to come through the wall and into your service void, I also put a bit of plastic conduit through the makeup just so I could then seal the conduit to the building, then using intumescent seal a little bead around the cable on the outside just to stop air leakage through the conduit. I only used intumescent sealant as it was specifically designed for use around cable. 

 

 

Edited by Carrerahill
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@dnb @TonyTGreat info in this thread guys, thank you. One follow up question I need a bit of advice on…I plan on putting external lights at the same height as the internal ceiling safety zone. The cables would be run in that zone (batten service void), pass through the timber framed/rendered wall (260mm) and terminate directly into the light fitting

 

Do I need to joint and change to swa before the cable passes through the wall or can I continue in t&e but put in a short length of metal/plastic conduit?

Do I need to put a box and blanking plate on the inside wall surface to show presence of cables even though it’s in the safety zone?


Cheers

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