How to fit a back box
Updated: October 2026
You have the box and you are about to mark the wall, and the plate on the existing point may still be live. How to fit a back box starts with proving the circuit dead, then with the hole the wall actually allows, and it stops when the cable, the earth, or the wall is outside a simple replacement. This page is that sequence for a UK single accessory. It does not rank the three listings. Prices and stars stay on the [Wall box comparison](/hub/electrical-equipment/wall-box). If you have not yet chosen flush metal, dry lining, or surface, do that on the [buying guide](/hub/electrical-equipment/wall-box/sub/wall-box-buying-guide) before you cut.
You have the box and you are about to mark the wall, and the plate on the existing point may still be live.
You have the box and you are about to mark the wall, and the plate on the existing point may still be live. How to fit a back box starts with proving the circuit dead, then with the hole the wall actually allows, and it stops when the cable, the earth, or the wall is outside a simple replacement. This page is that sequence for a UK single accessory. It does not rank the three listings. Prices and stars stay on the Wall box comparison. If you have not yet chosen flush metal, dry lining, or surface, do that on the buying guide before you cut.
Our top picks
| Badge | Product | Mounting | Fixings | Earth terminal | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Evoges Evoges EDB1G35 dry lining box | Dry lining, spring lugs | Spring lugs | Not stated | 9.6 | about £8.99 | View offer |
| Best value |  Lyvia Lyvia 25 mm metal wall box | Flush, screw-in | Knockout cable entries | Earth fixing connection stated | 9.4 | about £3.68 | View offer |
 LEENUE LEENUE 32 mm surface wall box | Surface, screw-in | 2 screws. Wall plugs not listed | Not stated on the listing | 9.4 | about £6.99 | View offer |
On this page
Isolate before the plate comes off
Turn the circuit off at the consumer unit and prove the conductors dead with a tester you know how to use, before the faceplate screws come out. In England and Wales, Approved Document P makes a new circuit, a consumer-unit change, or an alteration in a bathroom-style special location notifiable. Scotland uses building standard 4.5 and BS 7671, not the English Part P schemes. Northern Ireland has its own building regulations.
Plasterboard: cut, then the lugs
On a hollow stud wall the usual box is a dry lining box, not a metal flush box with nothing solid behind the board. Mark the outline from the box, not from a larger guess, and check you are not about to cut a noggin, a pipe, or the cable you have just proved dead. Cut the hole so the rim of the box sits on the face. The lug sequence in UK how-to pages, and in Evoges reviews for the EDB1G35, is the same idea: push the side tags in, insert the box, then push the tags out so they grip the back of the plasterboard. “Tool-free” on a listing is a description of the lugs. It is not a fire rating.
Metal flush and surface boxes are a different job
A galvanised flush box, such as the Lyvia 25 mm listing, is chased into masonry so the front edge finishes where the plate can sit flat. Knock out only the entries you will use, fit grommets on metal edges, and do not leave bare cable against a raw knockout. The bullets state an earth fixing connection. NHBC guidance distinguishes a socket, where the earth is made at the accessory, from many switches, where the earth is made at the metal box. Sleeve any bare protective conductor. A surface pattress, such as the LEENUE 32 mm box, is drilled and plugged on the face of the wall. That pack includes two screws and does not list wall plugs, so buy plugs that match the wall rather than forcing the screws. If the new plate needs a deeper box than the chase you inherited, the depth choice is on 25 mm or 35 mm, not a reason to crush the terminals.
Stop and get a professional
Stop if the point is in a bathroom or another special location, if you are adding a circuit, or if you are changing the consumer unit. Stop if you cannot identify the earth or the conductors, if the cable is damaged, undersized, or cloth-insulated in a way you do not recognise, or if the old box was the only thing holding a loose termination. Stop if the wall may be fire-resisting. Approved Document B expects tested fire-stopping where a fire-separating wall is penetrated. An ordinary dry lining box, including the Evoges lug box, is not that test. A flue, a metal stud you cannot identify, or suspected asbestos is the same stop. When the box type itself is still wrong for the wall, settle that on metal or dry lining before you enlarge the hole.
Common questions
Do I isolate before I remove the old plate?
Yes. Isolate at the consumer unit and prove the conductors dead before the plate screws come out. The box you are fitting does not make the old cables safe, and a switch in the room is not an isolator. If you cannot prove dead, or more than one circuit appears behind the plate, stop and get an electrician. The rest of this sequence is for a circuit you have already proved dead.
How do the dry lining lugs actually work?
You push the side lugs in so the box can pass through the hole, you seat the rim on the face of the plasterboard, and you push the lugs back out so they clamp the rear of the board. Evoges reviews describe that push-in, insert, push-out order. One buyer had no instructions in the pack. The lugs need a hollow wall and a board they can grip. They do not screw into brick.
Where does the earth go on a metal box?
A metal box needs a sound connection to the circuit protective conductor. The Lyvia bullets state an earth fixing connection. NHBC notes put the socket earth at the accessory and often put a switch earth at the metal box. Sleeve bare earths. If the lug has sheared, as in one Lyvia review, replace the box rather than leaving the terminal unused. On a plastic box the earth usually ends on the accessory.
What if I am only replacing a damaged box?
Match the old mounting and a depth the plate still accepts, prove the circuit dead, and transfer the same conductors to the same duties. In England and Wales that like-for-like work outside a special location is generally not notifiable, and it still has to be safe. Scotland and Northern Ireland are not the English Part P scheme. If the cable is damaged or you are moving the point, it is no longer a straight replacement.
What if the wall is fire-rated plasterboard?
Do not cut it with an ordinary dry lining box. A fire-separating wall needs a tested fire-stop, and Approved Document B is the England-and-Wales frame for that. The Evoges listing does not claim a fire rating, and an easy lug fit is not a fire test. If you are not sure whether the wall is a compartment, ask before you cut.
Related pages
Sources
Public UK sources are listed below. Shelf prices and star lines are the amazon.co.uk figures checked on 21 October 2026.
- BS 4662: boxes for flush mounting of electrical accessories (retrieved 21 October 2026)
- BEAMA Technical Bulletin: selection of boxes (retrieved 21 October 2026)
- Approved Document P, electrical safety (retrieved 21 October 2026)
- IET: Part P frequently asked questions (retrieved 21 October 2026)
- IET: Part P in Scotland and Northern Ireland (retrieved 21 October 2026)
- Electrical Equipment (Safety) Regulations 2016 (retrieved 21 October 2026)
- Socket Store: what is a back box (retrieved 21 October 2026)
- NHBC: earth bonding of metal back boxes (retrieved 21 October 2026)