Cooker Circuit Calculator — Diversity, Cable Size, and MCB Rating for Cooking Appliances

A freestanding electric cooker or a hob-and-oven combination is normally fed by a dedicated radial circuit from the consumer unit to a cooker control unit or connection unit, then on to the appliance. On paper the loads look enormous — a large range cooker can total 14kW or more, a nominal 60A+ at 230V — yet cooker circuits have run happily on 30A and 32A protective devices for decades.

The reason is how cooking appliances actually behave. Every ring, oven, and grill is thermostatically controlled: elements heat up at full power, then cycle on and off to hold temperature. And it is rare for every element to be on together even at the peak of cooking a family meal. The sustained current the circuit really sees is far below the appliance's rated maximum.

Circuit design recognises this with a diversity allowance for household cooking appliances — a standard method for converting the rated current into a realistic assessed current for sizing the circuit. The calculator above applies it automatically when you add a cooker as a load.

The standard diversity allowance used for household cooking appliances works like this:

Two important boundaries. First, this is a household allowance — commercial kitchens and catering equipment are assessed on their actual duty, usually with little or no diversity. Second, the allowance is for cooking appliances fed from the circuit: where a hob and oven share one cooker circuit, the diversity applies to their combined rated current.

Diversity for the cooker is one part of assessing the whole installation — the same exercise covers sockets, water heating, and showers (which get no diversity). The diversity factor calculator and maximum demand calculator handle the full picture.

A customer's new range cooker is rated 14.4kW, and the cooker control unit has a socket outlet. Here is the full assessment:

So a cooker with a nominal current of 62.6A assesses to 30.8A — and a 32A device with cable sized accordingly is the typical result. That is the whole story of why most domestic cookers, even large ones, sit on 32A circuits.

The same cooker without a socket on the control unit assesses to 25.8A, and a smaller 10kW cooker (43.5A full load) with a socket assesses to 10 + 0.30 x 33.5 + 5 = 25.1A. Run your own appliance through the calculator above.

Once the assessed current is known, the circuit is designed like any other radial: the protective device is rated at or above the assessed current, and the cable carries at least the device rating after correction factors.

Derating is the usual trap in kitchens: cooker cables routed behind ovens, through insulated walls, or bunched with other circuits lose capacity. The cable sizing calculator applies the correction factors so the 6mm²-or-10mm² decision is based on the actual route.

Practical points on the control end of the circuit:

• A means of isolation — accepted practice is a double-pole cooker switch or control unit within easy reach of the appliance but not directly above a hob, so it can be operated in an emergency without reaching over hot pans.
• The socket on the control unit — older cooker control units often include a 13A socket. If it is there, the diversity assessment adds 5A for it. Modern installations frequently use a plain double-pole switch instead, with kitchen sockets on their own circuits.
• RCD protection — BS 7671 requires 30mA RCD additional protection for socket outlets rated up to 32A, which covers a control unit incorporating a socket. In a modern consumer unit the cooker circuit will typically be on an RCBO in any case.
• Connection to the appliance — freestanding cookers connect via a cooker outlet plate with enough slack to pull the appliance out for cleaning; built-in ovens and hobs follow the manufacturer's connection instructions.

Modern kitchens split cooking across separate appliances, which raises the "one circuit or two?" question:

• Induction hobs — ratings of 7.4kW are common. Many models offer power management that caps total draw, but the circuit should be designed for the appliance's connected rating unless it is configured and documented otherwise. Follow the manufacturer's instructions on the required supply.
• Single built-in ovens — many are under 3kW and designed for connection to a 13A supply; check the manufacturer's instructions. Larger double ovens need their own dedicated circuit.
• Hob and oven on one cooker circuit — a long-standing accepted approach where both are within the same kitchen: the diversity allowance is applied to the combined rated current, and each appliance connects via a suitable outlet from the shared circuit. Run the combined figure through the calculator.
• Separate circuits — the cleaner modern choice where board space allows: hob on one circuit sized for its rating with diversity, oven on another.

Whichever arrangement you choose, the assessed demand feeds into the installation's overall maximum demand — check the whole board with the maximum demand calculator before adding other large loads like a shower or an EV charger.