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Topic Title: Wooden Back Boxes
Topic Summary: Are these acceptable ref BS7671
Created On: 16 January 2013 07:35 PM
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 16 January 2013 07:35 PM
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Thripster

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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
 16 January 2013 07:43 PM
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daveparry1

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

Dave.
 16 January 2013 07:55 PM
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Thripster

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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
 16 January 2013 07:59 PM
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primo

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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.
 16 January 2013 08:10 PM
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Legh

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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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 16 January 2013 08:23 PM
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kj scott

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

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 16 January 2013 08:28 PM
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sparkiemike

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

In a test according to BS 476-4, a specimen of building material is placed in a furnace at a temperature of 750 °C. For the specimen to be considered non-combustible, sustained flaming on it must not persist for more than 10 s and the consequent temperature rise in the furnace must not exceed 50 °C.


So it is unlikley that your enclosure containing wood, would meet the criteria
 16 January 2013 09:00 PM
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Thripster

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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
 16 January 2013 09:09 PM
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Fm

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Paramount partitions
 17 January 2013 08:57 AM
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geov

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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?
 17 January 2013 10:07 AM
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AJJewsbury

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Originally posted by: sparkiemike

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



In a test according to BS 476-4, a specimen of building material is placed in a furnace at a temperature of 750 °C. For the specimen to be considered non-combustible, sustained flaming on it must not persist for more than 10 s and the consequent temperature rise in the furnace must not exceed 50 °C.




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

I wonder if a plastic dry-lining box would pass such a test...
- Andy.
 17 January 2013 11:34 AM
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maltrefor

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Originally posted by: Thripster

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


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?

http://www.promain.co.uk/specs...%20I%20P%20T%20TDS.pdf

Edited: 17 January 2013 at 09:51 PM by maltrefor
 17 January 2013 06:11 PM
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prophet

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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!)
 17 January 2013 09:50 PM
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rocknroll

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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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leave nothing but footprints!"
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 18 January 2013 09:33 AM
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kj scott

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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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 18 January 2013 04:52 PM
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aligarjon

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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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 18 January 2013 05:33 PM
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spinlondon

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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?
 18 January 2013 05:59 PM
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Thripster

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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
 18 January 2013 07:00 PM
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Legh

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Originally posted by: aligarjon

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


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."
 19 January 2013 11:38 AM
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potential

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Originally posted by: spinlondon
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?


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.
IET » Wiring and the regulations » Wooden Back Boxes

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