Three-Phase Load Balancer

List your loads, assign each to L1, L2 or L3 (or a balanced three-phase load), and see the current on every phase, the percentage imbalance and the neutral current. Auto-balance spreads single-phase loads across the phases for you.

Guidance only. Results are estimates based on the figures you enter and published tables. All electrical work must be designed, checked and tested by a qualified electrician to the regulations that apply where you are (e.g. BS 7671, NEC).

Supply

V
Line–line 398 V
A
Breaker / supply rating, e.g. 32, 63, 125, 400 A.
Ratings:

Loads

Watts or amps are per unit. For a “3φ balanced” load enter the unit's total watts (split evenly across the three phases) or its line current in amps. Lock a row to keep it on its phase when auto-balancing. Your list is saved in this browser.

Load Value Unit Qty PF Phase A / phase
CSV columns: name,value,unit,qty,pf,phase,locked — unit is W or A; phase is L1, L2, L3 or 3P.

Phase Loading

Imbalance (NEMA)
—
Max deviation from mean ÷ mean
Spread (max − min)
—
Neutral current
—
Phasor sum, fundamental only
Total load
—

Notes & References

  • Per-unit current. Single-phase: I = P ÷ (U0 × PF). Balanced three-phase: I = P ÷ (√3 × U × PF) on each line. Phase currents are the phasor sum of the loads on that phase, each lagging its phase voltage by arccos(PF). Leading (capacitive) loads are treated as lagging, which is the usual planning assumption.
  • Imbalance. “NEMA” is the NEMA MG 1 style definition applied to current: largest deviation of any phase from the average of the three, divided by the average. The spread figure is simply the highest phase minus the lowest, also shown as a percentage of the highest.
  • Neutral current is the phasor sum IL1 + IL2 + IL3. For loads with the same power factor this reduces to IN = √(I1² + I2² + I3² − I1I2 − I2I3 − I3I1).
  • Harmonics. LED drivers, moving-light and video power supplies and other switch-mode loads draw third-harmonic (triplen) currents. These are in phase on all three lines, so they add in the neutral instead of cancelling. With a lot of electronic load the real neutral current can be well above the figure shown here and can even exceed the phase current, even on a perfectly balanced system. BS 7671 Appendix 4 gives rating factors for cables carrying triple-harmonic currents; do not use a reduced-size neutral on these circuits.
  • Auto-balance uses a greedy “largest first” method: every single-phase unit (each item of a quantity) is placed in turn on the phase with the lowest current. It can split a row across phases. It is a good starting point, not guaranteed optimal, and it ignores practical things like which distro outlets are free.
  • 120/208 V: loads connected line-to-line (208 V single-phase) are not modelled; enter those as balanced three-phase or split them by hand.
  • Related tools: Power Calculator, Cable Gauge Calculator, Generator Sizing & Fuel.
  • This is guidance for planning temporary distribution. It does not replace BS 7671, BS 7909 or the judgement of a competent person.