Why does a 10 kW cooker only need a 32 A circuit?

Because of diversity. The IET On-Site Guide (OSG Appendix A, Reg 12.4.2) diversity formula for household cooking appliances is: first 10 A at 100% + remainder of total connected current at 30% + 5 A if the cooker control unit includes a socket-outlet. For a 10 kW cooker (43.5 A nameplate), this gives a diversified design current of about 25 A — well within a 32 A circuit. The diversity reflects the reality that cookers cycle elements on and off rather than running at full power continuously.

Can I use diversity for an induction hob?

Yes — induction hobs are still cookers for BS 7671 / IET On-Site Guide purposes. Apply the same diversity formula. Induction hobs do switch more quickly than ceramic hobs and have higher peak draws during boost mode, but the average load is still well below nameplate. The diversity calculation handles this. For a 7.2 kW induction hob alongside a 3 kW oven, diversified Id ≈ 18-22 A depending on whether a socket-outlet is included.

Do I need a 30 mA RCD on the cooker circuit?

If the cooker control unit has a 13 A socket-outlet, yes — Regulation 411.3.3 requires 30 mA RCD on any socket-outlet circuit intended for general use up to 32 A. If the cable run is concealed in walls at less than 50 mm depth without earthed metallic covering, Regulation 522.6.202 also requires 30 mA RCD. In practice, most modern UK domestic cooker circuits use a 32 A or 40 A Type A 30 mA RCBO which satisfies both requirements simultaneously.

Where do I position the cooker control unit?

BS 7671 does not specify an exact distance, but practical installation guidance is clear: within 2 m of the appliance, to the side (never directly above the hob), at chest height (typically 1.2–1.4 m above floor level). Mounting the control switch directly above the cooker is explicitly flagged as a common installation defect — heat, steam, and cleaning products from the hob degrade the unit and make it unsafe to reach while the hob is in use. A common position is 100–300 mm offset to one side of the cooker on the wall.

What's the difference between a CCU with and without a socket-outlet?

A CCU with a 13 A socket-outlet (often labelled "cooker control unit with socket") provides both isolation for the cooker AND a kitchen socket-outlet on the same face plate. Convenient for a kettle / toaster near the cooker. A CCU without a socket-outlet is purely an isolator. The choice affects diversity calculation (5 A more for the socket-outlet version) and the kitchen socket-outlet layout overall. In most modern kitchens, the dedicated cooker socket-outlet is on a separate ring final circuit and the CCU is just an isolator — but the combined unit remains common in smaller kitchens.

Do I need a separate cooker circuit if I have a Range cooker?

Yes — almost always. Range cookers (especially all-electric or induction Range models) have connected loads in the 15-25 kW range, well above what can be served by sharing a circuit with anything else. The diversified design current still gives a manageable cable size (10 mm² typically, sometimes 16 mm² for very large installations), but the circuit must be dedicated. The protective device is typically 40 A or 45 A. Verify with the cooker manufacturer's installation instructions — many large Range cookers specify exact circuit and cable requirements.

Does the cooker circuit need an isolator if I have a CCU?

The cooker control unit IS the isolator — that's its primary function. A separate isolator is not required. The CCU provides double-pole isolation for the cooker, mounted where the user (or an electrician working on the cooker) can reach it. This is similar to the dedicated shower isolator requirement (Regulation 701.512.3 for showers), but cooker isolation is a practical accessibility requirement rather than a Section 7-specific regulation.

CABLE SIZING

Cable Size for a Cooker Circuit (With Diversity)

Cooker circuits differ from showers and EV chargers in one critical way: BS 7671 permits diversity. A 10 kW cooker rated nameplate-current of 43 A typically only needs a 32 A protective device and 6 mm² cable after the diversity calculation. This guide explains the IET On-Site Guide diversity formula, cooker control unit selection, and the practical UK domestic sizing.

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11 min readUpdated 2026-06-10Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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What size cable do I need for a cooker circuit?

For most UK domestic single-oven and four-burner-hob installations, 6 mm² twin-and-earth (6242Y) on a 32 A protective device is correct after applying BS 7671 / IET On-Site Guide diversity. A 10 kW cooker draws 43.5 A at nameplate but diversifies to about 25 A, so the circuit is sized for 25 A — not 50 A. Large Range cookers and double-oven setups may need 10 mm² on a 40 A or 45 A device.

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Key Takeaways

1Cooker circuits get DIVERSITY under BS 7671 / IET On-Site Guide — first 10 A taken at 100%, remainder at 30%, plus 5 A for any cooker control unit with a socket-outlet.
2Most UK domestic single-oven + 4-burner hob installations end up at a diversified design current around 25-30 A — easily served by a 32 A protective device and 6 mm² cable on a typical run.
3Larger installations (double oven + 5-burner hob, Range cookers, induction hobs with built-in extractor) may require 10 mm² and a 40 A or 45 A protective device.
4A standard "cooker control unit" with built-in 13 A socket-outlet adds 5 A to the diversified design current and must have its socket-outlet on 30 mA RCD protection per Regulation 411.3.3.
5BS 7671:2018+A4:2026 Regulation 411.3.4 adds 30 mA RCD protection on AC luminaire final circuits in domestic premises — but the cooker circuit itself is not directly affected unless the cooker control unit also feeds a kitchen luminaire (rare).
6The cooker control unit must be positioned within 2 m of the appliance but NOT directly above the hob — mounting directly above is a documented common installation defect (heat, steam, cleaning exposure).
7When testing Zs on site, apply the GN3 0.80 correction factor to the tabulated Table 41.3 limit. For a 32 A Type B MCB, the tabulated limit is 1.37 Ω, giving a cold-measured site limit of 1.10 Ω.

01 · Cable Sizing

Why Diversity Matters for Cooker Circuits

Cookers, unlike showers and EV chargers, do not operate at full nameplate rating continuously. A 10 kW cooker has multiple elements (oven, grill, hob rings) that are individually controlled — most users have only some elements on at any time, and even those elements thermostatically cycle on and off rather than running continuously. BS 7671 and the IET On-Site Guide recognise this through the diversity formula.

The IET On-Site Guide diversity formula for cookers (OSG Appendix A, Reg 12.4.2)

Diversified current = first 10 A at 100% + remainder of total connected current at 30% + 5 A if the cooker control unit includes a socket-outlet. Source: OSG Appendix A, Reg 12.4.2 (household cooking appliance demand calculation). For a 10 kW (43.5 A) cooker on a control unit with a socket: Id = 10 + (43.5 - 10) × 0.30 + 5 = 10 + 10.05 + 5 ≈ 25 A.

The diversified current is the design current Ib used for cable sizing and protective device selection — NOT the nameplate full-load current. This is why a 10 kW cooker that would seem to need a 50 A circuit ends up sized for a 32 A circuit in practice.

**Cooker / household cooking appliance** → diversity allowed. First 10 A at 100%, remainder at 30%, +5 A for a socket-outlet on the control unit. Size on the diversified current.
**Electric shower** → NO diversity. A continuous load — size on the full nameplate current.
**EV charger** → NO diversity. Treated as a continuous load — size on the full rated current.
**Immersion heater** → NO diversity on the dedicated circuit. Continuous thermostatic load — size on full load.

Confusing diversity rules between these loads is one of the most common cable-sizing errors. Diversity is for discontinuous, thermostatically-cycled cooking loads — not for the continuous heating loads they are often grouped with on a job.

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02 · Cable Sizing

The Short Answer

Match the combined nameplate load to the cable and protective device. These are the typical UK domestic outcomes after the diversity calculation — always confirm with a full design for your specific run length, install method and the cooker manufacturer's instructions.

Quick reference — combined load → cable → device

Single oven + 4-burner hob (≈8–10 kW): 6 mm² T&E, 32 A. · Single oven + 5-burner hob / small Range (10–13 kW): 6 mm² short runs, 10 mm² beyond ≈15 m. · Double oven + 5-burner hob / large Range (14–18 kW): 10 mm², 40 A. · Very large or commercial-spec Range (20 kW+): 10 mm² minimum, sometimes 16 mm² — verify the design.

**Single oven + 4-burner ceramic / induction hob (typically 8-10 kW combined nameplate)** → 6 mm² twin-and-earth with 32 A protective device on a short run.
**Single oven + 5-burner hob OR small Range cooker (10-13 kW combined)** → 6 mm² for short runs, 10 mm² for longer runs (>15 m) or where derating applies.
**Double oven + 5-burner hob, or large Range cooker (14-18 kW combined)** → 10 mm² with 40 A protective device.
**Commercial-spec or very large Range (20+ kW)** → 10 mm² minimum, possibly 16 mm² depending on diversity calculation and run length. Verify.

Run length matters: a 10 mm² choice for the "10–13 kW" band is usually driven by voltage drop on a long run, not by current-carrying capacity. Check it against the voltage drop calculator and the cable sizing calculator before committing.

03 · Cable Sizing

Diversity Worked Example — 10 kW Cooker + Hob

A typical UK kitchen: built-in single oven 3 kW + 4-burner ceramic hob 7 kW = 10 kW combined connected load. Cooker control unit includes a 13 A socket-outlet. 230 V single-phase supply, 12 m cable run from consumer unit.

**Full-load current** If = 10,000 / 230 = 43.5 A. (Would need a 50 A circuit if there were no diversity — but there is.)
**Apply IET diversity** — first 10 A at 100% = 10 A. Remainder of full load = 43.5 - 10 = 33.5 A. Apply 30% = 33.5 × 0.30 = 10.05 A. Add the socket-outlet 5 A. Diversified current Id = 10 + 10.05 + 5 = 25.05 A.
**Design current Ib = 25 A** (rounded). Select protective device: 32 A Type B MCB or 32 A 30 mA Type A RCBO (next standard rating at or above Ib).
**Cable selection** — 6 mm² flat twin-and-earth (6242Y), reference method C (clipped direct). Its tabulated current-carrying capacity from BS 7671 Table 4D5 comfortably exceeds the 25 A design current, so the cable passes on current-carrying capacity with plenty of headroom.
**Voltage drop** — using the 6 mm² mV/A/m figure from BS 7671 Appendix 4, Section 6.4. For 12 m at 25 A: 7.3 × 25 × 12 / 1000 = 2.19 V ≈ 0.95% of 230 V — well inside the 5% (11.5 V) limit for a non-lighting final circuit. Passes.
**Disconnection time** — 32 A Type B MCB: tabulated limit Zs ≤ 1.37 Ω (Table 41.3, Cmin = 0.95). When measuring at ambient on site, apply the GN3 0.80 correction factor — cold-measured site limit = 1.37 × 0.80 = 1.10 Ω. 12 m of 6 mm² with proper bonding will typically measure 0.4–0.6 Ω at the cooker. Passes.

Conclusion

6 mm² twin-and-earth with a 32 A 30 mA Type A RCBO is the standard UK installation for a typical 10 kW cooker + hob with cooker control unit including a socket-outlet on a short run.

04 · Cable Sizing

Larger Cookers and Range Cookers

Range cookers and double-oven installations have higher connected loads. The diversity calculation still applies but the diversified current rises:

**Double oven (5 kW) + 5-burner gas hob (1 kW for ignition) + extractor (0.3 kW) ≈ 6.3 kW** — diversified Id ≈ 10 + (27.4 - 10) × 0.3 + 5 = 20.2 A. Easily 6 mm² with 25 A protective device.
**Double oven (5 kW) + 5-burner ceramic hob (8 kW) = 13 kW** — diversified Id ≈ 10 + (56.5 - 10) × 0.3 + 5 = 28.95 A. 6 mm² with 32 A RCBO.
**Range cooker (e.g. AGA all-electric, induction Range) 18 kW** — diversified Id ≈ 10 + (78.3 - 10) × 0.3 + 5 = 35.5 A. 10 mm² with 40 A RCBO.
**Very large commercial-spec installation (20+ kW)** — diversified Id approaching 40-45 A. 10 mm² typically, but verify the design.

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05 · Cable Sizing

Cooker Control Unit Selection

A cooker control unit (CCU) is a double-pole switch unit that isolates the cooker. Two main types in UK domestic use:

**CCU with 13 A socket-outlet** — combines isolation + a kitchen socket-outlet on the same plate. The socket-outlet adds 5 A to the diversity calculation per the IET formula. The socket-outlet is RCD-protected by the cooker circuit's 30 mA RCBO.
**CCU without socket-outlet** — pure isolator. No socket-outlet, no 5 A diversity addition. Common where a separate ring final circuit serves the rest of the kitchen sockets.
**Pole configuration** — always double-pole, isolating both line and neutral.
**Current rating** — at least equal to the protective device rating. Common UK ratings are 32 A and 45 A.
**Position** — to the side of the cooker, within 2 m of the appliance, but NOT directly above the hob. Mounting the control switch directly above the cooker is a documented common installation defect (heat, steam, and cleaning exposure; noted as a common mistake in practical work guidance). Typical UK practice is at chest height, 100–300 mm offset to the side. Regulation 536.3 requires that devices in the same installation coordinate with each other, so ensure any RCBO on the cooker circuit is selected for compatibility with the CCU rating.

06 · Cable Sizing

RCD Protection and A4:2026

A cooker circuit's RCD requirements come from a combination of regulations:

**Regulation 411.3.3** — 30 mA RCD on any socket-outlet circuit intended for general use up to 32 A. The 13 A socket-outlet in a cooker control unit falls under this — RCD protection required.
**Regulation 522.6.202** — 30 mA RCD on cables concealed in walls at depth less than 50 mm, per Table 52.1. The alternative compliance route under Regulation 522.6.204 removes this RCD requirement for the cable-run portion: a cable with an earthed metallic covering (e.g. SWA to BS 5467 / BS 6724, or MICC to BS EN 60702-1) satisfies 522.6.204(a) in place of the RCD. Standard flat 6242Y without such covering falls under 522.6.202 and needs RCD protection for any section concealed at less than 50 mm.
**Regulation 411.3.4 (new in A4:2026)** — 30 mA RCD on AC luminaire final circuits in domestic premises. Direct cooker circuits don't feed luminaires, so this regulation doesn't directly apply unless an installer has mis-wired a kitchen light from the cooker control unit (rare and non-compliant).
**Type selection** — Type A or higher recommended for modern cookers with electronic temperature controls and induction hobs. Type AC may not reliably detect DC fault current components from induction hob switching.

07 · Cable Sizing

Common Cooker Cable Sizing Mistakes

**Ignoring diversity and sizing for full nameplate load** — over-specifying. A 10 kW cooker on full-load current basis would need a 50 A circuit, but with proper diversity calculation a 32 A circuit on 6 mm² is correct.
**Applying diversity to a non-cooker high-power load** — diversity is specific to cookers and certain other discontinuous loads. EV chargers, electric showers, immersion heaters are CONTINUOUS loads and DO NOT get diversity — size them on full-load current.
**Forgetting the 5 A addition for a socket-outlet CCU** — adding the socket on the cooker control unit increases Id by 5 A in the IET formula. Missing this can leave the circuit slightly undersized.
**Wrong Type AC RCD for modern induction hob** — Type AC RCDs can fail to trip on DC fault components from induction hob switching electronics. Specify Type A or higher.
**Sharing cooker circuit with other loads** — a cooker circuit should be dedicated. Sharing with kitchen sockets or other loads invalidates the diversity calculation (the assumption that the cooker is the dominant load no longer holds).
**Mounting the control switch directly above the hob** — heat, steam, and cleaning spray from the hob damages the CCU and makes it harder to reach safely. Install to the side, within 2 m, at chest height. Mounting directly above the appliance is explicitly flagged as a common defect in practical installation guidance.
**Ignoring the GN3 0.80 correction when testing Zs** — the tabulated Zs limit (e.g. 1.37 Ω for a 32 A Type B MCB) is a hot-conductor value. Site measurements at ambient must pass the cold-measured limit: 1.37 × 0.80 = 1.10 Ω. Failing to apply this factor is a common on-site mistake that can result in a circuit that passes the meter but fails under fault conditions.

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Cable Size for a Cooker Circuit (With Diversity)

What size cable do I need for a cooker circuit?

Key Takeaways

Why Diversity Matters for Cooker Circuits

The IET On-Site Guide diversity formula for cookers (OSG Appendix A, Reg 12.4.2)

Get the BS 7671 A4:2026 Cheat Sheet — free

The Short Answer

Quick reference — combined load → cable → device

Diversity Worked Example — 10 kW Cooker + Hob

Conclusion

Larger Cookers and Range Cookers

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Cooker Control Unit Selection

RCD Protection and A4:2026

Common Cooker Cable Sizing Mistakes

Frequently Asked Questions

Why does a 10 kW cooker only need a 32 A circuit?

Can I use diversity for an induction hob?

Do I need a 30 mA RCD on the cooker circuit?

Where do I position the cooker control unit?

What's the difference between a CCU with and without a socket-outlet?

Do I need a separate cooker circuit if I have a Range cooker?

Does the cooker circuit need an isolator if I have a CCU?

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Size cooker circuits with diversity built in