Diversity & load balancing
Not everything runs at once, and loads should be spread across phases — the basis of sizing and balance.
Diversity
Diversity recognises that not every load in an installation runs at full power at the same time. The realistic maximum demand is less than the simple sum of every connected load — so circuits and supplies are sized for likely simultaneous use, not the theoretical total.
Load balancing
On a three-phase board, single-phase loads should be spread evenly across the three phases. If they're concentrated on one phase, that phase runs hot, its conductor and the neutral carry more current, and it nuisance-trips — while the others sit lightly loaded.
Why it matters
Both ideas underpin a healthy installation: diversity keeps it economically and sensibly sized; balancing keeps a three-phase board running cool and evenly. An unbalanced board or an overloaded phase is a common commercial fault.
Sizing decisions (cable, protection, maximum demand) are governed by the wiring rules and are licensed design work — verify against your current standards.
Safety first
Sizing and maximum-demand decisions are licensed design work governed by the wiring rules — verify against your current standards. Don't overload a phase.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Related faults
Three-phase distribution board badly unbalanced
One phase of a three-phase board runs much hotter / higher current than the others — nuisance tripping on that phase, a hot neutral, or a warm phase conductor at the board.
Sub-main keeps tripping the main board
A sub-board's incoming protective device (or the main feeding it) trips — taking out everything downstream — and you need to tell overload from a fault on the sub-main or sub-board.
Three-phase equipment running hot from supply imbalance
Three-phase equipment (motors, heaters, large gear) runs hotter than expected or nuisance-trips, traced to a voltage/current imbalance between phases rather than the equipment itself.
Related definitions
Three-phase power
Three AC supplies offset in time, giving smooth power and a rotating field for motors.
Distribution & sub-mains
How power is split from the main board into final circuits and sub-boards, with protection at each level.
Neutral vs earth
The neutral carries return current; earth is for safety. Confusing them causes real, dangerous faults.