Knightsbridge 1 Gang 27mm Architrave Galvanised Steel Back Box

The Knightsbridge 1-gang 27mm architrave back box is a shallow galvanised steel enclosure designed for mounting electrical accessories in narrow wall spaces, doorframes and architrave positions where a standard 35mm or 47mm back box will not fit. The box is pressed from 1mm-thick galvanised steel and measures 73mm high by 27mm wide, with a 27mm recessed depth.

Architrave back boxes are typically installed in timber doorframes, on narrow walls between rooms, or in partition walls where stud depth is limited. The 27mm profile allows a socket or switch to sit flush with the wall surface while keeping the total installation depth below 30mm. The galvanised steel construction provides structural rigidity and earth continuity, with an integrated earth terminal fixed inside the box for connecting the earth conductor from the circuit cable to the faceplate earth.

The box features 16mm knockouts on the top and bottom faces for cable entry, allowing twin-and-earth or singles to be fed in from above or below depending on the cable route. The knockouts are pre-scored and can be removed with a screwdriver or punch. The galvanised finish resists corrosion in damp environments and provides a conductive surface for earthing. The box accepts standard UK 1-gang faceplates and accessory mounting lugs.

Product Specification Sheet

What's the difference between an architrave box and a standard back box?

An architrave box has a much shallower depth (27mm vs 35mm or 47mm) and is designed for installation in narrow wall spaces like doorframes where a standard back box would protrude too far or not fit at all. The trade-off is reduced internal volume for cable terminations.

Will this fit in a standard timber doorframe?

Yes. Most UK timber doorframes use 32mm or 44mm timber sections, so the 27mm recessed depth of this box will sit within the frame thickness. The box should be chased into the timber or mounted in a pre-cut aperture with the faceplate sitting flush with the architrave moulding.

Does it need an earth connection?

Yes. The box includes an integrated earth terminal for connecting the circuit earth conductor to the metal enclosure and onward to the faceplate earth terminal. This is a requirement under BS 7671 for metal back boxes.

What cable size can the knockouts accept?

The 16mm knockouts will accept standard UK twin-and-earth cable up to 2.5mm² or singles in 20mm conduit. For larger cables or multiple cable entries, the knockout may need enlarging with a file or step drill.