Running watts are not enough
Portable AC and dehumidifiers can need a large start allowance. Size the generator for start behaviour as well as the steady load.
Electrical calculator · generator / kVA / compressor / start current
Generator kVA & Compressor Start Calculator
Size a generator for portable AC, dehumidifiers, fans and heaters with a start-current allowance rather than only running watts.
For event sites, emergency cooling, flood drying and temporary power jobs.
Field notes
Field notes for Generator kVA + start current
Practical checks to run before this calculator result turns into a site decision.
Stagger starts where possible
If the result is marginal, a staged start plan can be cheaper and safer than simply oversizing the generator.
Check voltage sag symptoms
Hard starts, dimming, alarms or nuisance trips point to generator/load mismatch, long leads or poor phase allocation.
FAQ
Generator kVA + start current FAQ
Short answers written for UK temporary electrical and HVAC planning work.
What is the Generator kVA + start current used for?
Size a generator for portable AC, dehumidifiers, fans and heaters with a start-current allowance rather than only running watts. 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 supply rating, protective device rating, cable length, voltage drop, start current, phase balance and the condition of temporary leads or distribution boards. 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.
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Select a likely temporary connection class based on load current, voltage, environment and duty cycle.