Start with the weakest part of the temporary supply
The limiting point is often not the headline supply size. Check plug rating, extension length, reel state, transformer rating, RCD/RCBO sharing and the smallest protective device in the chain.
Electrical calculator · three-phase / phase balance / temporary DB
Three-Phase Temporary Load Imbalance Optimizer
Allocate single-phase heaters, dehumidifiers, fans and portable AC units across L1/L2/L3 to reduce imbalance and nuisance trips.
For 32A, 63A and 125A temporary distribution boards with mixed 230V loads.
Field notes
Field notes for Three-phase load balancer
Practical checks to run before this calculator result turns into a site decision.
Allow for ugly starts and wet-site behaviour
Compressors, pumps and long leads can behave badly at start-up. Treat amber results as a prompt to split circuits, stagger starts or move the load closer to the board.
Keep a short job-file note
Record the entered load, assumed voltage, cable run and any decision to split equipment. It makes later fault finding and handover conversations much cleaner.
FAQ
Three-phase load balancer FAQ
Short answers written for UK temporary electrical and HVAC planning work.
What is the Three-phase load balancer used for?
Allocate single-phase heaters, dehumidifiers, fans and portable AC units across L1/L2/L3 to reduce imbalance and nuisance trips. 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.
Next tools in this workflow
See super flows
Calculator · 110V / site transformer
110V transformer heater check
Check whether a 110V site transformer can realistically power temporary heaters, dehumidifiers, fans or drying kit without overload or ugly voltage drop.
Calculator · RCD / earth leakage
RCD leakage budget
Estimate cumulative leakage from compressors, dehumidifiers, portable AC, heaters, pumps and long wet leads before stacking everything behind one RCD.
Calculator · generator / kVA
Generator kVA + start current
Size a generator for portable AC, dehumidifiers, fans and heaters with a start-current allowance rather than only running watts.
Calculator · 13A / 16A
Connector selector
Select a likely temporary connection class based on load current, voltage, environment and duty cycle.