A back box is the metal or plastic box that is fitted into a wall. The front plate of a socket or a switch is then attached to the back box.
Which Back Box do I Need?
There are two main materials used for back boxes. There are metal back boxes and plastic back boxes.
Plastic Back Boxes
The plastic ones are used with stud partition wall, where the wall is made of a wooden stud frame and is finished with plasterboard. The hole is usually cut our of the plasterboard. There are two lugs (yellow in the picture on the right) which clasp onto to plasterboard tightly as the screw from the face plate is tightened to the wall.
Metal Back Boxes
The metal back boxes are used in solid walls, such as stone, brick and breeze block walls. The cut-out for these metal back boxes are normally chiselled out of the wall material. The lugs on these back boxes are metal and normally fixed. As you tighten the screws on the face plate, it fits the face plate tight against the wall.
There are many different types of back boxes, but the most used two are single and double back boxes. While this covers most scenarios there are a number of others, such as twin singles and round back boxes that are used on other occasions.
What depth back box will I need?
There are again a number of different depth options available for your back box. We would normally suggest if you are replacing your current back box it is worth replacing like-for-like, unless you are changing the plate too. Some plates need deeper back boxes. Read on for more details on those.
If you are fitting new back boxes we would always say don't scrimp on the depth. It makes fitting the switches and sockets easier - your electrician will thank you for it later!
Standard Sockets and Switches
We would recommend the following depths for standard switches and sockets:
Socket & Dimmers: 25mm
USB Sockets: 35mm
Shaver & Cooker Switches: 32mm
Flat, Screwless and Slim Sockets and Switches
For slim, screwless or flat plates you will need deeper back boxes, so we would suggest the following sizes:
Socket & Dimmers 35mm
USB Sockets, Shaver & Cooker Switches 47mm
Please note: We would recommend sitting the metal back boxes slightly further back in the wall for flat plate sockets and switches. This will allow the flat plates to sit tightly against the wall. Failing to do this may mean the plate sits slightly off the wall, which will spoil the effect of the flat plates.
Under certain circumstance you may not be able to, or want to, put back boxes in the wall. When this is the case you can also buy surface mounted back boxes, also know as pattress boxes. These are often available in the same finish as the sockets and switches, so they match the front plate, but be aware these are not universal sizes, so some plates, especially larger plates, may not sit well on the front of them. Check the details before buying.
Cable entry points for surface mounted back boxes
As most of the pattress boxes we sell are finished with a decorative finish (often in metal) the cable entry point on these surface mounted back boxes are in the back of the box, not on the sides, as is often the case with standard back boxes.
While a competent DIY-er can fit back boxes please take care when cutting or drilling holes in wall. Watch out for hidden cables and pipes. Wear the appropriate safety equipment and if in doubt always consult a qualified electrician!