Also in: Disaster Response and Recovery
Power Distro Per-Leg Loading
Current per leg, percent of service rating, headroom.
Example
You enter
- Total connected load (W) 12000
- Service voltage (V, line-line for 3-phase) 208
- Phase three
- Service rating (A per leg) 60
- Power factor 1
- Continuous-derate target 0.8
You get
- Current per leg 33.31
- Pct load 55.5
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeCurrent per leg, percent of service rating, headroom, and a pass/fail against the 80% continuous limit for stage/event temporary power, 1-phase or 3-phase.
Formula or table1-phase I = W/(V*PF); 3-phase I = W/(sqrt(3)*V_LL*PF); %load = I/rating*100; continuous limit = rating x the entered continuous-derate target (0.80 for the NEC 80% rule).
Source and editionFirst-principles AC power (P = V*I*PF; 3-phase adds sqrt(3)); the NEC continuous-load 80% rule and temporary-power Articles 520/525, by name.
Free accessNFPA 70 free read-only at nfpa.org/freeaccess; a qualified electrician and the AHJ govern temporary power.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field nameswatts, voltage_v, phase, rating_a, pf, derate, amps_per_leg, pct_load
- Balanced legs per-leg current assumes a balanced load (per-phase loads are not entered)AC power