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Discuss Which box to use please in the Electrical Forum area at ElectriciansForums.net

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Having a slight argument with a supposed electrician

Now I always thought when flush fitting an internal double socket to to an external wall. It's safer to use the metal boxes

Now the guys is going to use a plastic box (I actually thought these were for stud walls.

I asked if it would be safer just to surface mount and he went through me saying metal boxes are shite they rust. (Weird how they've been used for alot of years)

I thought it would be best to ask here

Thanks in advance
 
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If its a masonry wall then its normal practice to fit a metal knock out box. The box wont rust unless you have no DPC.
Dry lining box for stud walls or if flat profile sockets are being fitted a noggin and knock out box.
 

DPG

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Are you saying he sinks normal plastic back boxes into masonry walls?
 
  • Thread Starter Thread Starter
  • #4
Thank you, and yeah it's masonry. Not sure about DPC

I'll ask him to use metal as it's already cost enough for this kitchen, don't want anything going wrong

John L
 
I would use a metal back box but for a second here let’s indulge discussion as to why plastic couldn’t be used. The early back boxes were metal because the metal conduit joined to it making the only earthing connection - single wire runs of what was [back then] live and neutral. That’s why the earth terminal is in the back, to bring it to the socket output (because there wasn’t a wire). It’s not the 1950’s - why not plastic back boxes?
 

littlespark

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Are we talking plastic drylining boxes with the adjustable lugs, fixed into brick... or is there a plastic version of the regular metal backboxes?
 

Andy78

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I would use a metal back box but for a second here let’s indulge discussion as to why plastic couldn’t be used. The early back boxes were metal because the metal conduit joined to it making the only earthing connection - single wire runs of what was [back then] live and neutral. That’s why the earth terminal is in the back, to bring it to the socket output (because there wasn’t a wire). It’s not the 1950’s - why not plastic back boxes?
With early conduit systems in domestic installs I have mostly seen wooden backboxes, not metal.

I have only ever seen a few metal boxes rusted to the point of it being an issue. Perhaps the location of the OP has a bearing on this ? Is the installer acting on experience ?
 

davesparks

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I would use a metal back box but for a second here let’s indulge discussion as to why plastic couldn’t be used. The early back boxes were metal because the metal conduit joined to it making the only earthing connection - single wire runs of what was [back then] live and neutral. That’s why the earth terminal is in the back, to bring it to the socket output (because there wasn’t a wire). It’s not the 1950’s - why not plastic back boxes?
At one time plastic 16mm single flush boxes were available for light switches in installations with no cpc.

The biggest reason not to use plastic flush boxes now is that either don't exist or are extremely rare if they do. A normal surface pattress is too big and too brittle to work as a flush box.
 

rolyberkin

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If an external wall of dubious quality (early white block or simply carp construction materials has been dot and dabbed with plasterboard I would probably use plastic back boxes as it would probably be a better fixing. Wouldn't use them routinely over metal back boxes.
 

Matthewd29

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Metal boxes are common practice because that's what we are used to but realistically there is no reason why he can't use a plastic box there is nothing wrong with it
 

davesparks

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Metal boxes are common practice because that's what we are used to but realistically there is no reason why he can't use a plastic box there is nothing wrong with it
It will be hard to get a neat finish around whatever is fitted to the box due to the plastic boxes available being the same size as the accessories as they are intended for surface mount use.
 

Matthewd29

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It will be hard to get a neat finish around whatever is fitted to the box due to the plastic boxes available being the same size as the accessories as they are intended for surface mount use.
In any case apart from the odd light switch I don't think I've ever seen it done
 
Certainly sounds unorthodox. Not necessarily wrong though, but I do wonder why you'd do it.
Are the walls drylined on a metal furring system or are they just standard plaster onto blockwork?
 
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