Electrical Load Schedule: engineer's guide
The load schedule turns a room-by-room equipment list into a phase-balanced demand kVA that drives transformer sizing, incoming breaker selection, and generator sizing.
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What this calculator does
The calculator accepts rows of connected loads with power factor and demand factor, distributes them across R/Y/B phases, sums the phase totals, and reports the maximum phase current and unbalance.
Formulas used
- Demand kW per row:
Pd = Pc × DF - Demand kVA per row:
Sd = Pd / cosφ - Phase current:
Iphase = ΣSd on phase / VLN - Unbalance %:
U = (Imax - Iavg) / Iavg × 100
Variables
- Pc = connected active power, kW
- DF = demand factor (fraction of Pc expected to run)
- VLN = line-to-neutral voltage
Worked example
Scenario: Panel with 20 rows of connected loads totalling 180 kW, average DF 0.7, average cosφ 0.9, 400/230 V four-wire.
- Diversified demand: 180 × 0.7 = 126 kW; Sd = 126 / 0.9 = 140 kVA
- Per-phase distribute the rows so R/Y/B kVA are within 10% of each other
- If R phase = 50 kVA, Y = 45 kVA, B = 45 kVA, IR = 50000 / 230 ≈ 217 A
- Select 250 A incomer with adjustable trip; verify voltage drop from incomer.
Common mistakes to avoid
- Applying one blanket DF to the whole panel instead of per row
- Placing all large single-phase loads on one phase
- Missing spare-way allowance for future additions
- Ignoring inrush of large motor rows during panel closing sequence
Frequently asked questions
Typical DF values?
Lighting 0.9, general power 0.7, HVAC 0.8, kitchen 0.6, motors 0.85, receptacles 0.5.
Acceptable phase unbalance?
Under 10% at panel level, under 3% at incomer for utility connection.
Spare capacity?
20 to 30% typical, higher if future fit-out is expected.
Standards and references
IEC 60364-3, BS 7671, NEC Article 220
Related tools on this site
Open the calculator that pairs with this guide: Electrical Load Schedule.
Verification note
This guide is planning support only. Final design must be verified against the applicable project specification, authority requirements, manufacturer data, and the standards cited above. Consult a licensed engineer for construction-issue calculations.