I am about to start installing IWI on the two external walls of our living room. There are three double 13amp sockets which need to be moved (plus TV aerial sockets). There will be 75mm of Celotex plus plasterboard so overall thickness approx 87mm. I intend to make a kind of extension box to house the new pattress (see attached photo of the prototype) and use WAGO connectors to extend the cables. The boxes will be secured to the wall using angle brackets.

My question is: is it safe to mount the pattresses inside wooden boxes? I didn't think it would be a problem as I have seen, for example, pattresses mounted on wooden noggins before but my wife just raised the question and put doubts in my mind!

I don't see what difference it would make - wooden houses have electricity?

Assuming your wifes concerns are the fire risk, AFAIK the vast majority of electrical fires in domestic wiring are at joints/connections. Adding connectors of any type adds to this risk, but that risk is likely quite low if the connection is done correctly. Assuming the cables come down the wall, cant you raise the sockets 50mm to gain enough length on the cable??

Posted By: philedgeAFAIK the vast majority of electrical fires in domestic wiring are at joints/connections.

+1
But in all the years of electrical work I've only had one connection go wrong - a WAGO connector melted along with the wire insulation at the connector point. some smoke but no fire/flames and the circuit stopped working as the connection failed. Cable insulation and connectors are supposed to the self extinguishing - in this case I guess they were.

Posted By: philedgeAssuming the cables come down the wall, cant you raise the sockets 50mm to gain enough length on the cable??

and so avoid the need for a wire extension.

Like lots of things - less joints = less risk

Jeff, the thermal conductivity of a steel rod is really high, 2500x more conducive than cellotex, so each 10mm dia rod is thermally equivalent to about 2 square feet of IWI - not what you want! As well as the heat loss, I'd be thinking about the cold spot causing condensation in the socket box.

I'd really be looking at using the plastic boxes with a flange that are recessed into the plasterboard and clamp onto it, requiring no other fixings, they are designed just for this job, like Tony's link.

Posted By: djh

Posted By: Jeff Buse surface mounted sockets but the wife is not keen on the latter though.

What's your wife's difficulty with these? We have a whole load and I doubt SWMBO is even aware we have!

I think normally she would not have thought strongly about this bar for a very recent, rather ill-timed and unfortunate event! We were away on holiday for a few days last week and after we checked into our hotel room we noticed that the bedside lights and the fridge were not working. I checked to see if the sockets were switched off and discovered that someone (presumably the cleaner) had pushed the bed against a surface mounted twin socket and had literally broken the thing in half!

However all's well that ends well:

I had a chat with a local electrician who I know quite well and trust his opinion.Coincidentally it appears that he has just done work at a house where the owner has done some IWI with Celotex. He said he refused to fit sockets within the insulation layer and insisted that the owner used surface mounted boxes attached to the plasterboard which was music to my ears! In addition I have since found a source of PVC surface mounted pattress boxes as opposed to the usual urea/formaldehyde (bakelite?) type and these are much more resilient. They cost about 2 to 3 times as much as the latter but have won the day!

Posted By: Jeff Bdiscovered that someone (presumably the cleaner) had pushed the bed against a surface mounted twin socket and had literally broken the thing in half!

Whoah! Not sure what would have happened with a [plug in a] socket mounted on a meatl backbox there?

However all's well that ends well

Glad to hear it :)

Posted By: Ed DaviesPosted By: philedge: “Assuming the cables come down the wall, cant you raise the sockets 50mm to gain enough length on the cable??”

Also, it's quite likely that current building regulations will call for the sockets to be higher than they currently are so they probably, at least in theory, ought to be raised as part of this work anyway. Haven't looked at the English regulations for a while but in Scotland they should be 400 mm above the floor:https://www.gov.scot/publications/building-standards-2017-domestic/4-safety/48-danger-from-accidents/" rel="nofollow" >https://www.gov.scot/publications/building-standards-2017-domestic/4-safety/48-danger-from-accidents/section 4.8.5.

English regs require it for new builds, but not for refurbs I believe. They are definitely more convenient once you get used to them, although arguably slightly uglier with more trailing wire.

Posted By: WillInAberdeen450mm in England - perhaps the people are 50mm taller down South?

If there is a suspended ground floor then the cables might run upwards from it to the sockets, rather than downward from the ceiling, our last 3 houses were wired like that.

Afaict it is very common for sockets to be recessed into insulated walls, so possibly different electricians would have different interpretations of the regulations. Perhaps the electrician was thinking about surface-mounting the cables? There is quite a significant derating factor applied to cables which run through insulation for more than a short distance.

Will - none of my cables will be actually buried in insulation. I am using WAGO connectors (never used them before - aren't they fantastic!) to provide "extensions" to reach the surface mounted pattress boxes via a hole cut in the insulation/plasterboard. I can seal where the cables enter the back of the boxes (and also the rear edges of the boxes) with intumescent mastic.

I went off the idea of chiselling the walls to release more of the cables once we had made the decision to go for surface mounted boxes rather than flush ones. Our cables definitely come down the walls.

Posted By: WillInAberdeen450mm in England - perhaps the people are 50mm taller down South?

We're probably just less fit and find it harder to bend down

Thinking a little more, I think the regs are written for people in wheelchairs and I have a friend who can't pick up things from the floor or manipulate his own shoes etc. Hence also the upwards limit of 1200 mm.

You have to use the right sort of wagos if you are burying them in the wall (as you are in this case). They have to be in a sealed box, not just the connectors on wire. i.e WAGOBOX® 221-4, or WAGOBOX®, not just the bare 222 or 773 connector.

I second all the advice to use plasterboard plastic backboxes, make sure it's vapourtight where the indent in the PUR is cut, avoid thermal bridging with metal or timber, and avoid connections if at all possible.
I did all mine with the plastic backboxes so I have flush sockets. I rewired to avoid connections (and tired 1960s cable insulation). Cabling is hidden behind skirting boards so doesn't go into base masonry wall at all.

http://wookware.org/pics/online/greenbldg/IWI-socket-taping.jpeg

Chiselling out of walls to allow extension of cables successful! Render was rather soft and therefore a straightforward job. Anyone need any WAGO connectors!?