Have any of you come across manufactured wooden back boxes before? Domestic situation, rewire, old couple with 96 year old mum afflicted with dementia requiring near full time care, 1962 house. Non load bearing walls fabricated using 2", square section, thinwall cardboard with wooden vertical supports (2" x 1 1/2") at 18" intervals. Switch plates screwed to back of wooden back box with wood screws. Twin core flat(s) run to each with separate, braided, uninsulated cpc terminated at switch. I am quite happy to put dry lining boxes in but not having dealt with this before I wondered whether the wall material is strong enough to support these. I therefore wondered what the implications would be if I simply used the existing wooden back boxes as far as the Regs go. An additional consideration is that the customer is keen to minimise damage to his decorating. Any of you come across this before and how would you tackle it?

Regards

They are very common in 40's & 50's properties. I wouldn't leave them in on a re-wire!

Dave.

Thanks Dave. I understand, in part, why you say that (fire risk, professional job etc) but (a) where do I stand with the regulations and (b) what method of fixing is feasible on 1/16" thick 'cardboard' walls that is going to be any better than the wooden back boxes?

Thanks for your views.


Neil

Regs wise not sure as every time I come across these I replace them with metal boxes. Thankfully, once the wood is removed you can usually get a 35mm box straight in there with only a bit of filler around the edge. I've never seen them in the wall structure you are talking about. Is it the honeycomb type cardboard wall? If so then they will take dry lining boxes.

You might look at surface mounting the cables in mini trunking and using something like gravity toggles to fix surface mounted accessory boxes otherwise you'll have to contend with all sorts of noggin type barriers inside the 'walls'

IMO, this sounds like one for a complete rewire.

Legh

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"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

The existing construction is unlikely to comply with 526.5, replacing the boxes would be the best option if rewiring.

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As far as regs go have a look at item iii of Reg 526.5.



So it is unlikley that your enclosure containing wood, would meet the criteria

Thanks for your help. Primo - yes honeycombed so info about dry lining boxes good. KJ and Sparkie - that has help me to make my mind up. Legh - it is a rewire as stated in OP - do not like sm trunking on wallpaper as is pig ugly and attracts dust.

Regards Neil

Paramount partitions

The paramount partition walling I have come across is/was more substantial than described in the OP - typically plasterboard sheet on either side with "eggbox" between - which I actually quite liked. Used extensively by Geo Wimpy in the '70's.

But maybe there is more than one type?

I wonder if a plastic dry-lining box would pass such a test...
- Andy.

I always thought that all hardwood enclosures were flame resistant as used also on the old Wylex consumer units but if not would a couple of coats of this surfice?

Link removed/specs...%20I%20P%20T%20TDS.pdf

Edited: 17 January 2013 at 09:51 PM by maltrefor

Easy to rewire, because you can force rods up the cavity. Dry lining boxes will do, but remember, the walls are about 2" thick so make sure you don't have two boxes back to back (learn by my mistakes!)

Wooden back boxes are not considered 'intrinsically unsafe' as they were constructed from treated hardwood sides and ply backing and generally scorch rather than burn.

Most of the recommended advice is when it is prudent to do so they should be changed, for example on a major refurbishment where decorating afterwards is required so they have been there for a long time without any problems why worry.

regards

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"Take nothing but a picture,
leave nothing but footprints!"
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"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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A the man falling from the top of the tower block said to people at their windows on the way down 'so far so good'.

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if rods don't give a good enough hole for your cables use a piece of oval plastic ducting, slide the cable down in it then pull it back out, it will fly up there. ive never come across noggins with this stuff. fasta fix box or a bit of grip fill with a metal box on the switches will be ok.

Gary

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Specialised Subject. The Bleedin Obvious. John Cleese

I'm not too sure that the back boxes have to be replaced.
Wilst we all know, that wood is cmbustible, so is plastic.
I haven't yet seen any plastic fire doors, most appear to be wood.
The containment system used in the two houses of parliament is wooden, to fit in with the decor.
Seems a bit over the top really to condemn something that has been working fine for 50 years.
I don't know whether that's a professional opinion or just a personal one?

Thanks for the info. Have removed the wooden back boxes to find thin noggins behind - 16mm steel fits fine for most for the others a crystal ball and sellotape. The original boxes relied on a short screw and plaster to retain - the replacements will do the same. Regards

You never know with prefabricated internal structures what you'll find under the surface.
However, I'll bow to those who know about egg boxes.....

Mini trunking certainly looks ruff but as far as a dust collector, that is a new one on me. Having said that, the SEB chaps used it all the time for rewires back in the 1980's

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

Yes I agree. I think it is just prejudice because the boxes are old.
However the main problem with wooden backboxes is that it is difficult to attach modern fittings.
At the time wooden boxes were fitted, electrical fittings were supplied with chromed wood screws.