Cable Buried in a Wall in a Kitchen
A kitchen refurbishment involves chasing a 2.5 mm² twin-and-earth cable into a plastered wall to supply a new double socket. The chase is about 30 mm deep, and the cable is covered by plaster with no earthed metallic covering or conduit. The socket is at 300 mm above floor level on a wall that is 1.2 m wide between a door frame and a corner. The circuit is protected by a 32 A MCB with a 30 mA RCD at the origin. The installer also plans to run a 6 mm² cable for a new electric cooker along the same wall, clipped to the surface at 150 mm above the floor, then up behind the units. The consumer unit is 8 m away, and the existing cooker circuit has been removed.
1. Evaluate the routing of the 2.5 mm² cable and the proposed cooker cable against the requirements for cables in walls and protection against electric shock.
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Socket cable in the wall. A cable buried in a wall at less than 50 mm depth without earthed metallic covering or mechanical protection must be protected by a 30 mA RCD, and it must be routed in a safe zone. The safe zones are within 150 mm of the top of the wall, within 150 mm of a corner, or directly above/below/adjacent to an accessory. The socket at 300 mm above floor level on a 1.2 m wide wall between a door frame and a corner: the vertical run from the socket must be within the safe zone above or below the socket, and horizontal runs must be within 150 mm of the ceiling or floor or a corner. The 30 mm chase is less than 50 mm, so RCD protection is required - it is present at the origin, which satisfies the requirement, but the RCD must be verified. The cable also needs to be in a recognized safe zone; if the chase runs diagonally, that is non-compliant.
Cooker cable. The 6 mm² cable clipped to the surface at 150 mm above the floor and then up behind units is not buried, so the 50 mm rule does not apply. However, it must be protected against mechanical damage, and surface runs in a kitchen should be in conduit or trunking where they are exposed to impact. The cable must be sized for the cooker load and the protective device; 6 mm² clipped direct may be adequate for a 32 A device, but the cooker's rating and the installation method must be checked. The cable must also be in a safe zone if it is concealed behind units, and the route must avoid thermal insulation.
Earthing and bonding. The kitchen may have extraneous-conductive-parts (metal water pipes, gas); main protective bonding must be present and sized correctly. Supplementary bonding is not normally required in a kitchen if main bonding and RCD protection are in place, but the metallic parts must be checked.
2. The installer says the RCD at the origin makes safe-zone routing unnecessary. Is that correct?
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No. RCD protection and safe-zone routing are separate requirements. The RCD protects against electric shock if a cable is penetrated, but it does not remove the requirement to route cables in prescribed safe zones or to provide earthed metallic covering or mechanical protection. A cable run diagonally across a wall, or outside a safe zone, is still non-compliant even with a 30 mA RCD, because the RCD is a backup measure and not a substitute for correct routing. The correct approach is to route the cable vertically or horizontally within a safe zone and rely on the RCD for the additional protection required for buried cables. The RCD must also be tested to confirm 30 mA operation within the required time.