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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

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 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 and Mercury.

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 a switch, socket or other wiring accessory is fixed to, holding the cable terminations behind the faceplate. Flush pattress boxes sit inside the wall, and surface pattress boxes, such as the Knightsbridge CU1610 in white thermoset resin, sit on the wall surface.

What depth back box do I need?

The depth the accessory states: slim switches fit a 16mm or 25mm box, while fused spurs differ by model. More cable in the box calls for a 35mm or 47mm box. Check the depth on the accessory's product page, and use an extension box where an existing box is too shallow.

What is a dry lining box?

A dry lining box fits a hole cut in plasterboard, gripping the board so no fixing into the wall behind is needed. Knightsbridge dry lining boxes such as the SN8370 at 35mm and SN8381 at 47mm are white PVC, certified to BS 5733, with 20mm knockouts for cable entry.

Do metal back boxes need to be earthed?

Metal back boxes are fitted with an earth terminal so the box can be connected to the circuit's protective conductor. Knightsbridge galvanised steel boxes such as the GSK225 and GSK27 state an earth terminal in their titles, and thermoset pattress boxes such as the SN1600 include one too.

Can I get a coloured surface pattress box?

Yes. Knightsbridge 1GSB and 2GSB polycarbonate surface boxes, 32mm deep, come in white, grey, brushed chrome, polished chrome and black, the black as the 2G 2GSBBK, so a surface-mounted switch or socket matches a metal faceplate. Knightsbridge pattress boxes such as the CU1400 and SN1400 come in white thermoset resin, with curved or square edges.

What is a back box extension?

An extension box, such as the Knightsbridge GSE225 2G or GSE25 1G, fits in front of an existing flush box to add 25mm of depth. It is used when a wall has been tiled or re-plastered, or when a deeper accessory replaces a shallow one without cutting the wall.

What is the difference between a flush and a surface back box?

A flush box is set into the wall so the faceplate sits flat against it, while a surface box sits on the wall face where the wall cannot be chased. Knightsbridge galvanised steel boxes such as the GSK225 are for flush fitting, and the 1GSB and 2GSB boxes for surface mounting.

Is there a weatherproof box for outdoor cable joints?

Yes. The Knightsbridge JB0016 is an IP68 24A inline weatherproof gel box for H07RNF cables, and the JB007BK and JB009BK are IP66 weatherproof outdoor enclosures in black polycarbonate; the JB007BK measures 86x74x62mm. For outdoor switches and sockets, see the outdoor electrical boxes collection.

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

Written by the West Midlands Electrics technical team

Updated

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