Cooker Circuits: Sizing and Wiring
A cooker rarely draws its full rated load, so diversity lets you size a sensible circuit — but you still need the right cable, protection and control unit.
An electric cooker or oven-and-hob combination can have a high connected load, but the elements are thermostatically controlled and rarely all on at once. BS 7671 diversity lets you size the circuit for the realistic demand rather than the nameplate total.
This guide works through sizing a cooker circuit with diversity, choosing the cable and protective device, and wiring the cooker control unit correctly.
Key takeaways
- Apply diversity — a cooker rarely draws its full connected load, so the design current is much lower than the nameplate.
- A common domestic cooker circuit is 6 mm² on a 32 A device, subject to the actual load and install method.
- The cooker control switch must be within reach — typically to the side of, not above, the appliance.
- A 13 A socket in the control unit is on the same circuit and counts in the diversity calculation.
- Size cable for the design current, applying correction factors and checking volt drop.
Applying diversity
The standard domestic cooker diversity allowance takes the first 10 A of the rated current at 100%, then 30% of the remainder, plus 5 A if the control unit has a socket. So a cooker rated at, say, 46 A works out to a design current well below its nameplate.
This is what lets a 6 mm² cable on a 32 A device serve a cooker that would otherwise look like it needs far more.
Design current, not nameplate
Size to the diversified design current — using the full connected load oversizes the cable and protection every time.
Cable and protection
With the design current known, size the cable for its current-carrying capacity under the actual installation method, apply any grouping or insulation correction factors, and check volt drop over the run. A 6 mm² cable on a 32 A protective device is common, but a long or bunched run may push you to 10 mm².
Confirm the disconnection time and earth fault loop impedance are within limits for the device.
The cooker control unit
The circuit terminates at a cooker control switch — a double-pole switch that isolates the cooker. It must be readily accessible and positioned so the user doesn't have to reach across the hob; to the side, roughly 300 mm to one side and about 2 m maximum from the appliance, is the usual practice.
If the control unit includes a 13 A socket, remember it's on the cooker circuit and was accounted for in the diversity calculation.
Connection and certification
Connect the cooker via an outlet plate where the appliance is hard-wired, keeping terminations tight and correctly rated. Test the circuit and record the results.
A new cooker circuit is notifiable under Part P and certified with an EIC; a like-for-like replacement on an existing circuit is a minor works job.
Size it in seconds
TradePlanr's cable sizing calculator applies the install method and correction factors so you land on the right cooker cable first time.
Frequently asked questions
What size cable for a cooker?
Commonly 6 mm² on a 32 A device for a typical domestic cooker after diversity, but it depends on the diversified design current, the installation method and volt drop. A long or bunched run may need 10 mm².
How does diversity work for a cooker?
Take the first 10 A of rated current at 100%, add 30% of the remainder, and add 5 A if the control unit has a socket. The result is the design current the circuit is sized to, which is well below the nameplate total.
Where should the cooker switch go?
Within easy reach and not above the appliance — typically to one side, around 300 mm from the edge of the cooker and no more than about 2 m away, so nobody reaches across the hob to isolate it.
From guidance to action
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