National Electric MFGTemporary power • HVAC load tools
Methodology

Electrical calculator · extension lead / cable reel / derating / 3kW heater

Temporary Heater Cable Reel Derating Calculator

Check whether a coiled, partly unwound or long extension reel is a bad match for a 2kW or 3kW temporary heater.

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For heater setups using 13A plugs, 16A commando leads or long extension reels.

Field notes

Field notes for Heater cable reel derating

Practical checks to run before this calculator result turns into a site decision.

Site check

A coiled reel is a heat trap

Temporary heaters can keep a reel warm for hours. Fully unwind reels and avoid hiding cable under materials or insulation.

Site check

Continuous load needs extra caution

A heater running all day is not the same as a short tool load. Watch 13A plugs, long leads and shared circuits.

Site check

Use the result to change the physical setup

The best fix is usually shorter cable, better connector class, full unwind, load split or a dedicated supply.

FAQ

Heater cable reel derating FAQ

Short answers written for UK temporary electrical and HVAC planning work.

What is the Heater cable reel derating used for?

Check whether a coiled, partly unwound or long extension reel is a bad match for a 2kW or 3kW temporary heater. It is mainly for temporary HVAC, drying, cooling and site-power planning, especially where a quick pre-check is needed before selecting equipment or changing a temporary setup.

Can this replace BS 7671 design, inspection or testing?

No. It is a competent-person planning aid only. Final decisions still need current BS 7671 requirements, manufacturer data, inspection, testing, risk assessment and the actual site conditions.

What should I verify before acting on the result?

Check heater nameplate kW, plug or commando rating, lead length, whether reels are fully unwound, circuit sharing and the installation environment. If any assumption is uncertain, use the result as a prompt to investigate rather than as permission to energise.

What does an amber or red result usually mean?

It normally means the margin is weak, an assumption is missing, or the load should be split, staged, moved closer to the supply, reduced or reviewed by a competent electrician before use.

Next tools in this workflow

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