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Back Boxes & Pattress

A back box, or pattress box, is the box behind a switch or socket that holds the wiring and gives the faceplate something to screw into. This range is Knightsbridge flush galvanised steel boxes, dry lining boxes for stud walls, and surface pattress boxes, including Knightsbridge thermoset resin and polycarbonate boxes and Mercury single surface back boxes, in 1-gang to multi-gang sizes and depths such as 16mm, 25mm, 35mm and 47mm, with mounting frames and weatherproof boxes.

Choosing Back Boxes & Pattress

A pattress box houses a switch or socket on or in the wall, and the boxes here include surface pattress boxes, galvanised steel flush boxes, plastic dry-lining boxes and weatherproof enclosures. Pick a box by the wall it goes in, the depth the accessory needs and whether the box will be seen.

Flush, dry lining or surface

Galvanised steel flush boxes, such as the Knightsbridge GSK225, are set into a chased masonry wall, and most carry an earth terminal. Dry lining boxes, such as the SN8381, clip into plasterboard on a stud wall. Surface pattress boxes sit on the wall where chasing is not possible.

Depth

Depth decides whether the accessory fits, so check the mounting depth the accessory states: a 16mm or 25mm box suits a slim switch, while fused spurs differ by model, so read the depth stated for the spur you choose. More cable in the box calls for a 35mm or 47mm box. Extension boxes such as the GSE225 add 25mm in front of an existing box.

Surface finish

Surface boxes include Knightsbridge white thermoset resin pattress boxes with curved or square edges, and Knightsbridge 1GSB and 2GSB polycarbonate boxes at 32mm deep, which come in white, grey, brushed chrome, polished chrome and black, the black as the 2G 2GSBBK, to match metal plates. Mercury single surface back boxes are the 429.923UK at 25mm and the 429.925UK at 47mm, both to BS EN60670-1.

BoxExampleDepth
Galvanised steel flush, 2GGSK22525mm
Galvanised steel, 1G + 2GGSK347D47mm
Dry lining, singleSN838147mm
Surface pattress, singleCU161047mm
Surface box, 1G1GSBBC32mm

Standards & compliance

Knightsbridge dry lining boxes cite BS 5733, and Knightsbridge galvanised steel boxes such as the GSK225, GSK25 and GSK335 are manufactured to EN 60670, the standard for boxes and enclosures for electrical accessories.

Frames and weatherproof boxes

Knightsbridge mounting frames, such as the CUG2F for 3G-4G, carry multi-gang plates. For outdoor joints, Knightsbridge IP68 gel junction boxes such as the JB0016 and IP66 weatherproof enclosures keep connections sealed, and the Mercury 429.920UK is an IP55 weatherproof box for sheltered outdoor positions.

Brands we stock in Back Boxes & Pattress

Connectix Cabling Systems, Hochiki, Knightsbridge, Mercury and RGL Electronics.

Knightsbridge supplies most of the boxes; other makers here include Mercury, Connectix Cabling Systems and Hochiki for back boxes.

Related categories

Match the box to what mounts in it: dimmer switches, fused spurs, and outdoor electrical boxes where the position is external.

Frequently asked questions

What is a pattress box?

A pattress box is the box behind a socket, switch or other wiring accessory that holds the wiring and gives the faceplate something to screw into. Flush boxes sit inside the wall, while surface boxes mount on top of it. The terms pattress box and back box are often used for the same thing. The range here includes flush, surface and dry lining boxes.

What size back box do I need?

A back box needs to match the gang size of the faceplate and be deep enough for the accessory and its cables. Single and double boxes suit standard plates, while larger grid plates and combination multimedia plates need multi-gang or dedicated boxes. Choose a deeper box for bulky accessories such as USB sockets, dimmers or fused spurs, or where several cables enter.

What types of pattress box are there?

The main types are metal flush boxes for solid walls, plastic dry lining boxes for plasterboard, and surface boxes that mount on the wall face. There are also architrave boxes for narrow positions and metal clad boxes for garages and workshops. Check the box suits the wall, the number of gangs and the depth needed. The range here includes galvanised steel, dry lining, surface and architrave boxes.

How do you fit a pattress box?

To fit a flush pattress box, mark its outline, chase or cut the wall to depth, then fix the box level with screws and plugs. In plasterboard, a dry lining box fits into a cut hole and grips the board with its lugs. Remove a knockout for the cable, fit a grommet, and isolate the circuit before any electrical work.

  • Established 1975
  • Birmingham trade counter
  • UK-only supply

Written by the West Midlands Electrics technical team

Updated

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