⚡ IEC + NEC Panel Schedule (Always Free)

⚡ Electrical Panel Load Calculator

Create a professional panel schedule: Demand, kVA, Current, Auto cable size (Cu/Al), Voltage Drop (R+X), Derating, and Breaker sizing.

🧮 Panel Load Schedule Builder

Switch updates voltage presets & cable list.
Pick preset to auto-fill voltage.
Used in calculations.
Auto from standard.
Row PF overrides this.
Row VD limit overrides this.
Derating factor applied.
Base: 30°C reference.
1.0 = single circuit.
# Description Load / Current Unit Type Phase DF PF Length (m) Conductor Cable (Auto) Ampacity (A) Derated (A) Demand kW kVA Current (A) VD Limit (%) VD (%) Breaker (A) Status Del
About Unit “A (Measured Current)”
Use A only when you already know the current (for example, a clamp meter reading). In this mode the tool treats the value as measured current and back-calculates kW/kVA using Voltage, PF, and Phase. For normal design work, keep Unit as kW / HP / kVA / W.
Total Demand (kW)
0.00
Total (kVA)
0.00
R Phase (A)
0.0
Y Phase (A)
0.0
B Phase (A)
0.0
Unbalance (%)
0.0
⚠️ ENGINEERING DISCLAIMER:
This calculator provides preliminary estimates only. Final design must verify manufacturer data, short-circuit rating, protection coordination, local amendments, and exact installation conditions.

Electrical Panel Load Calculator (IEC & NEC) – Complete Guide

This tool helps you create an electrical panel schedule and quickly estimate demand load, kVA, current, auto cable size (Copper/Aluminum), voltage drop, derated ampacity, and breaker sizing. It is designed for fast checks during design coordination, estimating, and site verification.

What Is a Panel Schedule?

A panel schedule is a circuit list showing connected load, demand factors, protective device size, and cable details. It is used for load balancing (R/Y/B), feeder sizing, and verifying voltage drop and ampacity compliance.

Standards: IEC vs NEC (Which One to Choose?)

  • IEC: Common for 230/400/415V systems used worldwide.
  • NEC: Common for 120/208/240/277/480V systems used in USA/Canada.

Switching the standard updates typical voltage presets and cable tables used for auto-selection.

How to Use This Tool (Step-by-Step)

  1. Select Standard (IEC or NEC) and choose a Voltage Preset (it auto-fills voltage).
  2. Set defaults: PF, VD Limit, installation method, ambient temperature, and grouping factor.
  3. Add rows and enter circuit data: description, load value, unit, type, phase, DF, PF, length, and conductor.
  4. Review outputs: Cable (Auto), Derated ampacity, VD (%), and Breaker (A).
  5. Use Export CSV to download the full schedule.

Load Units Explained (kW, HP, kVA, W, and A)

  • kW: Best default for lighting, sockets, heaters, UPS loads, and general power.
  • HP: Used for motors (pumps/fans/compressors). Conversion used: 1 HP = 0.746 kW.
  • kVA: Apparent power (DG/UPS/transformer nameplate). Conversion used: kW = kVA × PF.
  • W: Small loads. Conversion used: kW = W / 1000.
  • A (Measured Current): Use only when you already know current (verification mode). The tool back-calculates kW/kVA from voltage, PF, and phase.

What Does “VD Limit (%)” Mean?

VD Limit (%) is the maximum allowed voltage drop percentage. The tool compares calculated VD (%) to the limit. Typical targets: 3% for branch circuits and 5% total (feeder + branch) for overall system design.

Derating Factors (Why “Derated (A)” Is Lower Than Ampacity)

Cable tables show a base ampacity at standard reference conditions. Real projects need derating due to temperature, installation method, and grouping. The tool applies:

Derated Ampacity = Base Ampacity × ktemp × kinstall × kgroup

Breaker Sizing Logic

  • Normal / Continuous: Breaker ≥ 1.25 × Load Current
  • Motor: Breaker ≥ 2.5 × Load Current (simplified for starting allowance)

The final breaker is snapped to common standard steps (16A, 20A, 32A, 63A, 100A, 125A, etc.).

Formulas Used

3-Phase Current: I = (kW × 1000) / (√3 × V × PF)
1-Phase Current: I = (kW × 1000) / (V × PF)
Demand kW: Demand = Connected kW × DF
kVA: kVA = kW / PF

Voltage Drop (AC with Reactance):
VD% = (√3 × I × L × (R×cosφ + X×sinφ) / V) × 100   (for 3P)
VD% = (2 × I × L × (R×cosφ + X×sinφ) / V) × 100   (for 1P)
(L in km, R and X in Ω/km)

FAQ

When should I select Unit = “A (Measured Current)”?

Select it when you have a measured current value (site test / clamp meter) and you want to check cable size, voltage drop, and breaker selection. For design stage loads, use kW/HP/kVA/W instead.

What’s the difference between “Ampacity (A)” and “Derated (A)”?

Ampacity (A) is the base cable rating from the table. Derated (A) applies temperature, installation method, and grouping factors. The tool uses Derated (A) for the pass/fail check.

Why does the tool show “VD HIGH”?

“VD HIGH” means calculated voltage drop exceeds your VD Limit (%). Solutions: use a bigger cable, reduce length, improve PF, or move the panel closer to the load (shorter run).

📚 References

  • IEC 60364 (Low-voltage electrical installations)
  • NFPA 70 (National Electrical Code - NEC)

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