Back boxes on sockets/switches

[Arducius]

As far as I can see, back boxes are required on sockets and switches in houses and they have to be made from a non-combustible material. However, I can't see anything in the BSS about back boxes.

 

As there isn't a lot of space between my insulation and lining can I get away without using back boxes on sockets and switches, or will i need to dig out some space for the back boxes?

 

When we ripped out the old lining there were no back boxes and the sockets were screwed directly to the ply lining, so I'm thinking I can do the same thing now we are putting new lining back in. Is this a bad idea or am I worrying about nothing?

 

Thanks in advance!

[Robbo]

I would use back boxes, it's safer.

Edited October 18, 2013 by Robbo

[Paul C]

Personally I'd always use a back box for mains sockets and switches. If there's too little space to properly fit one behind the relevant panel, then the back box can sit in front of the panel and the socket/switch on it. I know its messier for looks and more obstructive etc but you can't simply leave it off if it doesn't fit! Actually I installed the socket underneath the gunnels (on the interior) with its back box, so that the leads exit outwards. There's a chance that certain plugs etc would fall out, but pragmatically its not happened (yet).

[Chalky]

I used back boxes for both mains and 12V circuits and attached tubular conduit to them to run the wiring it. It's made it a lot easier to upgrade / update the boat systems as things have evolved.

Edited October 18, 2013 by Chalky

[Arducius]

Thanks for the responses everyone. I think I'll see if I can use 25mm back boxes. If there isn't space I guess I can dig out some of the spray foam so create a cavity for the box to recess into.

 

The foam is on pretty thick on the hull sides (some places over 50mm) so I should be able to trim some back without losing too much heat or creating a particularly cold spot.

[Guest]

I had to dig a little foam away to get the back boxes in (plastic plasterboard type). No probs. in almost ten years.

[Arducius]

Something like this?

 

It looks as if the front plate screws into the thread set into the blue bits which clamp the back of the material you're attaching the socket to. If that's the case then this is what I'm looking for!

[jonathanA]

yep Dry lining back boxes are what I would use.

 

just need to be careful some of them are only designed for 12mm plasterboard plus a bit of plaster skim and I had a problem where i needed to mount something through some 18mm faced ply.

 

shouldn't be a problem through your normal lining ply.

[AndrewIC]

You may want to route (or chisel) a tiny rebate around the edge of the hole for the flange to sit in, otherwise the fitting may sit prou of the surface with the plastic flange showing a little.

[Guest]

Something like this?

 

It looks as if the front plate screws into the thread set into the blue bits which clamp the back of the material you're attaching the socket to. If that's the case then this is what I'm looking for!

They are the type that I used.

You may want to route (or chisel) a tiny rebate around the edge of the hole for the flange to sit in, otherwise the fitting may sit prou of the surface with the plastic flange showing a little.

Good idea, I should have done likewise.

[Ex- Member]

yep Dry lining back boxes are what I would use.

 

just need to be careful some of them are only designed for 12mm plasterboard plus a bit of plaster skim and I had a problem where i needed to mount something through some 18mm faced ply.

 

shouldn't be a problem through your normal lining ply.

 

Yeah good point!

 

I bought all my back boxes in a job lot, decent quality ones too not the cheapest. On the 9mm ply though they wouldn't bite tight when fitting the cover. I ended up gluing some plastic strip to the sliders to create a spacer and they all fitted ok. Some make back boxes will grip on thinner material though, so worth checking to save faffing around with glue and plastic LOL

[twelveeyedfish]

So where are your sockets? Above or below the gunwales?

I don't think there's enough depth above... Unless there are some incredibly shallow sockets. I last looked at some that were 35 millipedes deep.

[Pykebird]

I was always told 240v above gunnels, 12v can go below, not sure if this is correct!

[Ex- Member]

All our 240v is below the gunwale. I don't see or can work out any advantage in them being higher than the gunwale either.

 

The sockets and cabling are dead easy to fit below the gunwale, there simply plenty of space behind the panels, and clipping up cable is simple. Our sockets are all foot from floor level or higher. There are 240 switches on bulkhead walls though but running 12v lights.

 

If you're going to fit a lot of sockets it's worth making up a template for cutting out the holes, we made one from ply you screw to the wall and router around for a perfect neat cut out.

Edited October 21, 2013 by Julynian

[Arducius]

240v and 12v sockets are all going below the gunwale, with light switches and fittings above. The only exceptions being the sockets above the kitchen worktop, which may be incorporated into the units or they'll just go into the lining behind the worktop.

 

I picked up some 35mm dry lining back boxes at the weekend which look like they'll be prefect for the job. Thanks for all the help!

[Ex- Member]

240v and 12v sockets are all going below the gunwale, with light switches and fittings above. The only exceptions being the sockets above the kitchen worktop, which may be incorporated into the units or they'll just go into the lining behind the worktop.

 

I picked up some 35mm dry lining back boxes at the weekend which look like they'll be prefect for the job. Thanks for all the help!

 

With regard kitchen worktops and to avoid messing with upper linings We came across one of these and fitted it. It is very sturdy as well. The fact we don't use much 240 though and it can be put neatly hidden away it seemed the perfect solution. They are costly though I thing this one was well over £50 delivered.

 

 

 

 

I simply wired it off the feed to the fridge inside the back corner of the carousel corner unit. There's sometimes enough space behind drawer units for these too. We have a small 600w halogen oven we sometimes use in the summer and small hand held blending equipment which uses very little power. Also handy though for extra sockets for charging phones and the like.

[Arducius]

Julynian, I spotted that on your build blog - looks like a neat solution.

[Ex- Member]

Julynian, I spotted that on your build blog - looks like a neat solution.

 

Yeah it works really well, have just pm'd you.

[ditchcrawler]

I was always told 240v above gunnels, 12v can go below, not sure if this is correct!

Can't see why you cant put them where you like.

[Arducius]

Ditchcrawler, I was unable to find anything in the BSS about sockets full stop, let alone the positioning of them. I imagine separating your electrics in this manner helps when re-wiring etc, but is not a rule everyone must stick to.

[smileypete]

Best not to have them tooo low down, especially toward the stern!

 

Noticed that there's metal box flanges and reduced flange backboxes around, maybe worth the OP getting one of each for a trial.

 

http://www.tlc-direct.co.uk/Products/AP603.html

 

http://www.tlc-direct.co.uk/Products/MTFDLB2.html

 

cheers, Pete.

~smpt~

[Paul C]

Ditchcrawler, I was unable to find anything in the BSS about sockets full stop, let alone the positioning of them. I imagine separating your electrics in this manner helps when re-wiring etc, but is not a rule everyone must stick to.

 

Current American boat building regs (can't remember what they're called) require that 12V and mains electrics are separated by a conduit. However, the regs poorly define what a conduit is, to the extent that the sheathing around a mains cable (ie the secondary sheathing) counts as the required separation. I'll have a proper look at the regs at some point if someone's desparately interested. Its somewhat irrelevant for UK boats, especially existing ones (not new builds).

[Arducius]

Smileypete, I've gone for the second option. Low profile dry lining boxes should fit perfectly (I may have to trim a little spray foam back in some places). Started fitting the conduit over the weekend, so will have some sockets in soon (so far have been working off one socket by the batteries).

[Ex- Member]

I recall when wiring an electrician working at the boat yard advised me you just need to keep 12v and 240v apart by at least 6 inches and secure cables but use conduit where any 12 or 240 v cable crosses over each other or run through bulkheads together. This advice was given around 8 years ago though so something might have changed, if so I haven't heard of it.

[Guest]

I recall when wiring an electrician working at the boat yard advised me you just need to keep 12v and 240v apart by at least 6 inches and secure cables but use conduit where any 12 or 240 v cable crosses over each other or run through bulkheads together. This advice was given around 8 years ago though so something might have changed, if so I haven't heard of it.

Pretty much what I was advised about ten years ago. Again things may have changed.