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2 Gang 25mm Galvanised Steel Extension Box

£149
The RRP is the manufacturer's recommended retail price of the item.
Limited Stock
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Description

The Knightsbridge 2-gang 25mm galvanised steel extension box adds depth to flush-mounted wall boxes that have been sunk too deeply into plasterwork or need additional space to accommodate thicker wiring accessories. The box is fabricated from 1.0mm galvanised steel sheet and measures 132mm wide by 72mm high, matching the standard footprint of 2-gang UK back boxes.

Designed for residential and commercial electrical installations, the extension box sits between the flush back box and the faceplate, raising the mounting lugs by 25mm to bring them closer to the finished wall surface. This is common when a plasterer has set a back box too deep, when insulation has been added behind plasterboard, or when a deeper accessory such as a dimmer module or USB socket won't fit the original box depth. The single adjustable lug allows the faceplate to be levelled during fitting, and the multiple 20mm knockouts on all four sides provide cable entry points for surface conduit runs or additional cables that couldn't fit the original box.

The galvanised finish resists corrosion in damp wall cavities and provides a good earth continuity path through the steel frame. An earth terminal is fitted to the side of the box for bonding the earthing conductor. The 25mm depth is the most common extension size for correcting over-deep installations without protruding excessively from the wall — stacking multiple extension boxes is possible where greater depth is needed but check load ratings before doing so.

Specification
Height 72 mm
Width 132 mm
Recessed Depth 25 mm
Construction Steel
Earth Terminal Yes
Warranty 25
Downloads

Product Specification Sheet

Frequently Asked

When would I need an extension box?

Extension boxes are used when a flush back box has been sunk too deeply into the wall during first-fix, when insulation or plasterboard has been added over an existing box reducing its effective depth, or when a new deeper accessory such as a dimmer or USB socket won't fit the original box. The extension box raises the mounting lugs by 25mm to bring them closer to the finished wall surface.

Can I stack multiple extension boxes?

Yes, multiple extension boxes can be stacked to achieve greater depth, but check that the total weight of the extended box plus the accessory does not exceed safe loading for the original back box fixing. Heavy accessories on deeply extended boxes may require additional support.

Does the box include an earth terminal?

Yes. An earth terminal is fitted to the side of the box for bonding the main earthing conductor, ensuring continuity through the galvanised steel frame.

What are the 20mm knockouts for?

The knockouts on all four sides allow cable entry from surface conduit runs or additional cables that couldn't fit through the original back box. Standard 20mm conduit fittings and grommets fit the knockouts once removed.

Shipping & Returns

Free worldwide delivery

Free worldwide delivery on all orders over £99. International orders for third-party brand products may be subject to an additional courier surcharge based on volumetric weight, particularly on larger lighting fixtures — if a surcharge applies, our team will email you with the amount before dispatch and you can proceed or cancel for a full refund. See full delivery terms.

Returns

30-day returns window from delivery. As all our products are electrical or lighting goods, returned items must be inspected and recertified by a qualified electrician before resale — the cost of this inspection (25–40% of the item value) is deducted from your refund. Customers pay return shipping. Made-to-order, special-order and clearance items cannot be returned. See full returns policy.

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    Description

    The Knightsbridge 2-gang 25mm galvanised steel extension box adds depth to flush-mounted wall boxes that have been sunk too deeply into plasterwork or need additional space to accommodate thicker wiring accessories. The box is fabricated from 1.0mm galvanised steel sheet and measures 132mm wide by 72mm high, matching the standard footprint of 2-gang UK back boxes.

    Designed for residential and commercial electrical installations, the extension box sits between the flush back box and the faceplate, raising the mounting lugs by 25mm to bring them closer to the finished wall surface. This is common when a plasterer has set a back box too deep, when insulation has been added behind plasterboard, or when a deeper accessory such as a dimmer module or USB socket won't fit the original box depth. The single adjustable lug allows the faceplate to be levelled during fitting, and the multiple 20mm knockouts on all four sides provide cable entry points for surface conduit runs or additional cables that couldn't fit the original box.

    The galvanised finish resists corrosion in damp wall cavities and provides a good earth continuity path through the steel frame. An earth terminal is fitted to the side of the box for bonding the earthing conductor. The 25mm depth is the most common extension size for correcting over-deep installations without protruding excessively from the wall — stacking multiple extension boxes is possible where greater depth is needed but check load ratings before doing so.

    Specification
    Height 72 mm
    Width 132 mm
    Recessed Depth 25 mm
    Construction Steel
    Earth Terminal Yes
    Warranty 25
    Downloads

    Product Specification Sheet

    Frequently Asked

    When would I need an extension box?

    Extension boxes are used when a flush back box has been sunk too deeply into the wall during first-fix, when insulation or plasterboard has been added over an existing box reducing its effective depth, or when a new deeper accessory such as a dimmer or USB socket won't fit the original box. The extension box raises the mounting lugs by 25mm to bring them closer to the finished wall surface.

    Can I stack multiple extension boxes?

    Yes, multiple extension boxes can be stacked to achieve greater depth, but check that the total weight of the extended box plus the accessory does not exceed safe loading for the original back box fixing. Heavy accessories on deeply extended boxes may require additional support.

    Does the box include an earth terminal?

    Yes. An earth terminal is fitted to the side of the box for bonding the main earthing conductor, ensuring continuity through the galvanised steel frame.

    What are the 20mm knockouts for?

    The knockouts on all four sides allow cable entry from surface conduit runs or additional cables that couldn't fit through the original back box. Standard 20mm conduit fittings and grommets fit the knockouts once removed.

    Shipping & Returns

    Free worldwide delivery

    Free worldwide delivery on all orders over £99. International orders for third-party brand products may be subject to an additional courier surcharge based on volumetric weight, particularly on larger lighting fixtures — if a surcharge applies, our team will email you with the amount before dispatch and you can proceed or cancel for a full refund. See full delivery terms.

    Returns

    30-day returns window from delivery. As all our products are electrical or lighting goods, returned items must be inspected and recertified by a qualified electrician before resale — the cost of this inspection (25–40% of the item value) is deducted from your refund. Customers pay return shipping. Made-to-order, special-order and clearance items cannot be returned. See full returns policy.