Regulation for rewring back box?

The “where to buy” appears to exclude UK in the listings. 

The square box pictured appears to be a standard surface box whose outside dimensions look like 86 mm but with standard 2 3/8" or 60 mm screw fixing centres that are the same as standard metal knock out boxes. If you have standard 25 mm deep boxes fitted, these are available in 35 and 46 mm depths.

Regards

BOD

Hi Bod,

Thank you for your instant reply. I'm trying to follow, I have few additional questions:

1. Is the “not available in the UK” a red flag? If I can buy it, would I able to install it in a compliant way (as long as it has CE marking)?

2. For the practical solution, do you mean because both the 74 mm back box and 86 mm back box have 60mm screw fixing, this problem is effectively extending the depth of the standard back box and cut a bigger hole in the wall to be 86 mm?

3. Do you have any comments about compliance? If I do what I said in point 2, am I breaking any code? Do I need to find a certified electrician? 

I want check do I need part P certificate, or planning permission? 

Generally no - simply replacing an existing back box would not normally be notifiable under building regulations (and nothing to do with planning either).

The details vary depending on which nation you're in (Wales has building regs that tend to lag England's a bit and Scotland and NI have different approaches again) - the English ones for example can be found here: https://www.gov.uk/government/publications/electrical-safety-approved-document-p

Where work is notifiable under part P of the building regulations, there are a number of possible routes: Generally either pre-notifiy to your local building control dept (which costs a significant amount of money) and they'll make sure it's OK and issue a building control certificate (which is basically the method builders traditionally use for foundations and drains and the like and can also be used by DIYers); or you get a member of a registered competent persons scheme to do the work (they can then self-certify the work) - note that it's the membership of a scheme that counts rather than holding any particular certificates.  In theory there's also a third-party-verifier scheme where a registered competent person with an add-on to their registration can oversee the work (e.g. done by a DIYer) and issue a building regs certificate but they seem to be rather thin on the ground.

In any event you should be competent to do the work you undertake - whether it's notifiable or not. Competent isn't the same as qualified of course - a decent DIYer working well within their limitations could well be competent to carry out straight-forward electrical tasks without needing any electrical qualifications for instance.

If the property is privately rented there's no also a legal obligation to ensure that the electrical installation complies with the 18th Ed of the wiring regs - and in such cases if you were the tenant you'd perhaps need the landlord's permission too.

  - Andy.

For the practical solution, do you mean because both the 74 mm back box and 86 mm back box have 60mm screw fixing, this problem is effectively extending the depth of the standard back box and cut a bigger hole in the wall to be 86 mm?

I suspect it's more of a case of 74mm and 86mm being different ways of measuring the same thing (almost). 86mm is about the size of a normal plastic surface mounting box - which has relatively thick walls. Steel back boxes intended to be sunk into a wall are around 74mm on the outside but having thinner walls have about the same internal size as the 86mm plastic box.  The exact sizes vary slightly with brand - they're usually just referred to as 1 gang (or for the wider one 2-gang) boxes … according to the number of outlets the same size socket would have.

It sounds like you just need a deeper box of the same width/height.

    - Andy.

Sometimes a spacer may provide the solution.

Schneider Electric Lisse 1-Gang Spacer White | Light Switch Surrounds | Screwfix.co

Z.

planning permission is not needed for electrics unless changing the appearance of a listed building, so unless this is a historic castle, forget that.

Very few things are notifiable under building control part P. and replacing an existing back box with a bigger one, or a replacement of a cable that gets cut a bit short certainly isn't. 

New circuits and wiring in bathrooms are the triggers, come back for more info  if that applies. 

But your use of words like ‘code’ worries me - it sounds like you may be reading American texts, and their wiring methods are different, as is their approach to inspection and testing. Do not try and use 110V land methods here.

You could do worse than look in the catalogue of a well known supplier -example  https://www.tlc-direct.co.uk/Main_Index/Boxes_and_Enclosures_Index/index.html at the sort of wall boxes available,  and see what fits the switches you have in mind.

You do have to be competent of course, regardless of works being non-notifiable. 

IF you are unfamiliar with UK practice, then you could do worse than to read https://www.flameport.com/electric/lighting_circuits/index.cs4  JWs excellent guides to know what to expect.

And then come back here if it makes no sense.

Standard UK wall box dimensions are  reproduced here

https://www.canford.co.uk/TechZone/Article/BS1363-BS4662-Dimensions

Mike.

Note that surface mounted plastic pattress boxes have an external width/height that matches the accessory, while plastic/metal boxes which are embedded in the wall are narrower, so that the accessory forms a lip which overhangs the box and pushes against the plaster. So you might need a deeper box but unlikely a wider box.

If this is the same switch it is very deep.

Aqara wired switch installation (no zero line) - YouTube

Z.

Another solution for very deep accessories is to get the wall replastered with nice thick plaster over the metal boxes.

This is getting very complicated for a simple question!

As BOD said at the start, the pattress box shown is a surface mounted one. Alternatives are galvanised steel ones, which are set into the wall, and plastic ones for stud walls, which sit just proud of the plasterboard, which not only holds them in place, but also disappears if the wall is skimmed.

The spacing for the screws (M3.5) is the same for all of them.