Question 1

What cable size do I need for a 15kW range cooker?

Accepted Answer

A 15kW cooker draws 65.2A at full load, but with diversity applied the design current reduces to 31.6A (or 36.6A with a cooker control unit socket). A 6mm² cable (47A, Method C) is adequate with diversity, though many professionals prefer 10mm² for future-proofing. Always verify voltage drop on longer runs.

Question 2

Can one circuit feed both a hob and a separate oven?

Accepted Answer

Yes, provided the total load and diversity calculation supports it. Add the individual ratings together and apply the diversity formula to the combined total. A 7kW hob and 3kW oven (10kW combined) diversifies to 25.0A — comfortably within 6mm² capacity. However, some manufacturers require a dedicated supply, so always check the installation instructions.

Question 3

Why does my induction hob trip the RCD?

Accepted Answer

Induction hobs use high-frequency switching that can produce earth leakage currents up to 10mA per phase. On a shared 30mA RCD protecting multiple circuits, cumulative leakage can cause nuisance tripping. The solution is a dedicated Type A or Type F RCBO for the cooker circuit, isolating its leakage from other circuits.

Question 4

Do I apply diversity for the EIC maximum demand calculation?

Accepted Answer

Yes. The IET On-Site Guide diversity allowances are specifically intended for calculating maximum demand on domestic installations. Apply the cooker diversity formula (10A + 30% of remainder + 5A for socket) when completing the maximum demand section of the Electrical Installation Certificate.

Question 5

Is 6mm² enough for a cooker circuit?

Accepted Answer

In most domestic situations with diversity applied, yes. A 12kW cooker diversifies to 27.7A, well within the 47A rating of 6mm² (Method C). However, if the cable passes through thermal insulation or the run exceeds 20m, derating may push the requirement to 10mm². Always calculate rather than assume.

Question 6

What MCB rating do I need for a cooker circuit — 32A or 40A?

Accepted Answer

A 32A MCB on 6mm² cable is standard, suitable for cookers up to approximately 15kW after diversity. For larger range cookers where diversified current exceeds 32A, a 40A MCB on 10mm² is needed per IET On-Site Guide Table 1B.

Question 7

How does cooker diversity work in the UK?

Accepted Answer

The formula: take the first 10A at 100%, add 30% of the remainder, plus 5A if the cooker control unit has a socket. Example: 12kW cooker (52.2A) diversifies to 10 + 0.30 × (52.2 − 10) + 5 = 27.7A per IET On-Site Guide Table 1B.

Question 8

Do I need an RCBO for an induction hob?

Accepted Answer

While not mandatory, a dedicated Type A or Type F RCBO is strongly recommended. Induction hobs produce earth leakage up to 10mA through high-frequency switching. On a shared 30mA RCD, cumulative leakage causes nuisance tripping per Regulation 531.3.3.

Question 9

Can I connect a hob and oven on the same circuit?

Accepted Answer

Yes, provided the combined load after diversity supports it. A 7kW hob plus 3kW oven (10kW total, 43.5A) diversifies to 25A with socket — within 6mm² capacity. Check manufacturer instructions as some require dedicated supplies.

Cooker Circuit Calculator

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Quick Reference — Cooker Diversity

Practical Notes

Frequently Asked Questions