Voltage Drop Calculator
Calculate voltage drop in electrical circuits based on wire size, distance, and load current. Essential for electricians to ensure NEC compliance (max 3% for branch circuits).
Understanding Voltage Drop
As electricity travels through wire, the internal resistance of the wire causes the voltage to decrease. This is known as Voltage Drop. If the drop is too high, equipment may not run correctly, motors can overheat, and lights may flicker.
NEC Recommendations
The National Electrical Code (NEC) recommends the following limits for efficiency:
- Branch Circuits: Maximum 3% voltage drop.
- Feeders: Maximum 3% voltage drop.
- Total (Feeder + Branch): Maximum 5% voltage drop.
Formula Used
This calculator uses the K-factor method:
Vd = (Factor × K × I × L) / CM
- K: 12.9 (Copper) or 21.2 (Aluminum).
- I: Load Current in Amps.
- L: One-way length of the circuit in feet.
- CM: Circular Mils of the wire size.
- Factor: 2 for Single Phase, 1.732 for Three Phase.
? Frequently Asked Questions
A drop greater than 3% often results in noticeable dimming of lights and can cause motors to run hotter and burn out prematurely. It is the standard for efficiency and safety.
Copper is a better conductor (lower resistance) and is standard for most residential branch circuits. Aluminum is cheaper and lighter, often used for large feeders, but requires larger gauge sizes to carry the same current.
Technically yes (AC resistance varies in steel vs PVC conduit), but for general estimations and wire sizing, the DC resistance or standard K-factor method provided here is sufficient and industry standard.