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Calcimator

Feeder Sizing Calculator

Feeder conductor size from load amps and distance, with voltage drop check per NEC 215.2.

Inputs

%

Results

Conductor ampacity (A)

200

Actual voltage drop (V)3.99
Actual voltage drop (%)0.83
Min cmil for VD limit46,549
Parallel conductor runs1
Load current (A)200
Ampacity Keyampacity_cu
Ground Wire6 AWG
Sizing BasisAmpacity
How to Use This Calculator
  1. Enter the total feeder load in amperes from your panel schedule or load calculation.
  2. Enter the one-way distance in feet from the source panel to the load panel or equipment.
  3. Set the system voltage (208, 240, 277, or 480 V) and phase count (1 or 3).
  4. Select conductor material — copper (1) or aluminum (2) — and the maximum allowable voltage drop percentage (NEC recommends 3%).
  5. Read the selected conductor ampacity, actual voltage drop in volts and percent, and whether parallel runs are required.

What each input means

Load current (amps)
Total feeder load in amperes.
One-way distance (ft)
One-way distance from source to load in feet.
System voltage (V)
System voltage (208, 240, 277, 480 typical).
Phases (1 or 3)
Single-phase (1) or three-phase (3).
Material (1=Cu, 2=Al)
1 = Copper (K=12.9), 2 = Aluminum (K=21.2).
Max voltage drop (%)
NEC recommends 3% max for feeders (5% total branch+feeder).

What each result means

Conductor ampacity (A)
Ampacity of the selected conductor from NEC Table 310.16.
Actual voltage drop (V)
Calculated voltage drop using Vd = 2KIL/cmil (or sqrt(3) for 3-phase).
Actual voltage drop (%)
Voltage drop as percentage of system voltage.
Min cmil for VD limit
Minimum conductor cmil area to stay within voltage drop limit.
Parallel conductor runs
Number of parallel conductor sets if single set insufficient.
Load current (A)
Input load current for reference.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Load current (amps) = 200, One-way distance (ft) = 150, System voltage (V) = 480, Phases (1 or 3) = 3 = 6 input(s) provided
  2. Calculate Conductor ampacity
    200 = 200
  3. Calculate Actual voltage drop
    Actual voltage drop = (phaseFactor * K * loadAmps * distanceFt) / finalConductor.cmil
    3.99 = 3.99
  4. Calculate Actual voltage drop
    Actual voltage drop = (actualVd / voltage) * 100
    0.83 = 0.83

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

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