Panel Board Calculator for Construction

Tip

Enter your loads, then calculate to see sizing guidance.

You can add spare capacity and a voltage-drop check for longer feeders.

Input Form

Panel Board Inputs

Responsive layout: 3 columns large, 2 medium, 1 mobile.

System

Select supply type used for the feeder.

Voltage (V)

Use line voltage for 3-phase calculations.

Power Factor

Typical range: 0.80–0.95 for mixed loads.

Efficiency

Use 0.90–0.98 when motors dominate.

Spare Capacity (%)

Adds margin for future growth and uncertainty.

Continuous Load Factor (%)

Common practice uses 125% for continuous loads.

Feeder Material

Used for ampacity and voltage-drop estimates.

Feeder Length (m)

Set 0 to skip voltage-drop checking.

Max Voltage Drop (%)

Common feeder target: 3% (project-dependent).

Branch Circuits Needed

Used to estimate recommended panel spaces.

Loads

Add up to 8 load groups

Demand Factor (DF) ranges 0.00–1.00.

Load name	Qty	Watts each	DF

Reset

Example

Sample input table

Use this as a starting point for quick estimates.

Load	Qty	Watts	DF	Connected (kW)	Demand (kW)
Lighting	60	40	0.90	2.400	2.160
Receptacles	30	180	0.50	5.400	2.700
Small motors	4	1500	0.80	6.000	4.800
HVAC	1	8000	1.00	8.000	8.000
Totals				21.800	17.660

Sample outcome

With 20% spare, PF 0.90, efficiency 0.95, and 400V 3‑phase, the design current is typically around the mid‑40A range, often leading to a 50–63A main breaker selection.

Formula Used

How the calculator works

Connected load (kW): sum of (Qty × Watts) ÷ 1000.
Demand load (kW): sum of (Qty × Watts × DF) ÷ 1000.
Spare allowance: Demand_with_spare = Demand × (1 + Spare% ÷ 100).
Current (A), 3‑phase: I = (kW × 1000) ÷ (√3 × V × PF × Eff).
Current (A), 1‑phase: I = (kW × 1000) ÷ (V × PF × Eff).
Design current: I_design = I × (Continuous% ÷ 100).
Breaker pick: next standard size ≥ I_design.
Voltage drop (estimate): uses conductor resistance from material and area, then computes % drop using feeder length.

This tool provides estimating guidance. Always verify with project specifications and applicable electrical standards.

How to Use

Step-by-step guidance

Select the system type and supply voltage.
Enter power factor and efficiency appropriate for your loads.
Set spare capacity for growth and uncertainty.
Add your load groups with quantity, watts, and demand factor.
Provide feeder length and a voltage-drop limit if needed.
Click Calculate to see results above the form.
Use the download buttons to save your report.

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