Cooker Circuit Guide: Cable Size, Fuse and Wiring UK

A cooker circuit is a dedicated radial circuit that runs from the distribution board (consumer unit) to a cooker control unit, which in turn supplies the cooker. It is one of the highest-current circuits in a domestic installation, and getting the cable sizing and protection right is essential for safety and compliance with BS 7671.

The standard domestic cooker circuit uses 6mm² twin and earth cable (6242Y) protected by a 32A MCB or RCBO at the distribution board. The circuit runs from the board to a cooker control unit (a double-pole switch, with or without a 13A socket outlet) mounted on the wall adjacent to the cooker. From the cooker control unit, a cable or flex connects to the cooker itself.

Unlike socket circuits, cooker circuits benefit from a diversity factor — you do not need to size the cable for the full rated current of the cooker, because not all elements run at full power simultaneously. This diversity calculation is one of the most important skills in domestic circuit design.

The cable size for a cooker circuit is determined by the design current (after diversity), the installation method (reference method), and the applicable correction factors from Appendix 4 of BS 7671.

Always verify the cable\'s current-carrying capacity against the actual installation conditions. A 6mm² cable clipped direct (Reference Method C) has a higher current-carrying capacity than the same cable enclosed in an insulated wall (Reference Method A). If the cable passes through loft insulation, the thermal insulation correction factor (Ci) can significantly reduce the capacity — you may need to increase to 10mm².

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Diversity is a design allowance that recognises that a cooker will not operate all its elements at full power simultaneously. The standard domestic cooker diversity formula from the IET On-Site Guide (Table A2) is:

This diversity calculation applies only when the cooker is the sole appliance on the circuit. If a hob and oven share the circuit, use the combined rated current of both appliances in the diversity calculation. The Elec-Mate diversity calculator handles this automatically.

The cooker control unit provides a means of local isolation for the cooker. BS 7671 requires every cooker to have a means of switching off within easy reach of the person using the cooker (BS 7671 Section 537).

For built-in hobs and ovens, the cooker control unit can serve both appliances. The hob is typically hardwired via a cable to the control unit, while the oven may connect via a plug and socket or a flex outlet plate positioned behind the appliance within the cabinetry.

A common question is whether a separate hob and a built-in oven can share a single cooker circuit. The answer is yes, provided:

If the combined load after diversity exceeds 32A (which is rare for a standard domestic hob and oven), you have two options: upgrade the circuit to 45A with 10mm² cable, or install separate dedicated circuits for the hob and oven. Separate circuits are also preferred when the hob and oven are in different locations within a large kitchen or when the client specifically wants independent circuits for each appliance.

The cooker circuit is protected at the distribution board by an MCB or RCBO. The requirements are:

BS 7671 Regulation 421.1.7, introduced in 2018, recommends arc fault detection devices (AFDDs) on single-phase socket-outlet circuits up to 32 A. Since A2:2022 AFDDs are required on single-phase socket-outlet circuits up to 32 A in high rise residential buildings, HMOs, purpose-built student accommodation and care homes. Elsewhere the regulation is advisory (it uses “recommending” rather than “shall”) but represents current best practice and is increasingly expected by building control and fire risk assessors.

For further detail on AFDD requirements across domestic installations, including which circuits are most likely to benefit, see the AFDD guide.

The cable route for a cooker circuit typically runs from the distribution board through the building structure to the kitchen, then to the cooker control unit position. The installation method determines the cable's current-carrying capacity and must be identified using the reference methods in Appendix 4 of BS 7671.

When routing the cable, observe the safe zones defined in BS 7671 for cables concealed in walls — within 150mm of the top of the wall, within 150mm of the corner, or running horizontally or vertically from an accessory. Cables outside these zones at a depth of less than 50mm must have 30mA RCD protection or mechanical protection (such as metal capping).

Voltage drop must be checked for every cooker circuit. The limit under BS 7671 is 5% of the nominal supply voltage — that is 11.5V for a 230V supply. The voltage drop depends on the cable size, the cable length, and the design current.

Voltage drop is rarely a problem on domestic cooker circuits because the cable run is usually short (under 20 metres). However, for properties where the distribution board is a long distance from the kitchen (large houses, barn conversions, outbuildings), voltage drop may dictate a larger cable size even though the current-carrying capacity of the smaller cable is adequate.