top of page

Voltage Drop Tables

Wire Size Selection for Long Runs

Why Voltage Drop Matters​

  • Distance vs. Power: Voltage drop occurs when electricity has to travel through a very long stretch of wire or cable. While this is rarely an issue for standard wiring inside your home, it becomes a significant factor when running power to distant points like an outdoor shed, a well pump, or a barn.

  • The Impact on Equipment: When voltage drops too low, your electrical devices can’t run at peak efficiency. You might notice lights flickering or appearing dim, and motors or appliances may struggle to start. Over time, this constant strain can actually shorten the lifespan of your equipment.

  • How to Prevent It: To keep your system running smoothly, you need to choose a wire size that minimizes resistance over long distances. To do this, you first need to determine your Load (Current):

  • Add up the total wattage of all the devices on that circuit.

  • Divide that total by the voltage (typically 120V or 240V).

  • The result is your Amperage (Amps).

120 Volt, Conductor size (AWG or kcmil)Single Phase, Max 3% Voltage Drop*

Length of Run

A/C
25'
50'
100'
150'
200'
AMP
Copper
14
12
10
8
6
15 AMP**
Copper
12
12
8
6
4
20 AMP**
Copper
10
10
6
4
4
30 AMP**
Copper
1
1
1
2/0
4/0
100 AMP**
Aluminum
1/0
1/0
2/0
4/0
300 MCM
100 AMP**
Copper
3/0
3/0
3/0
300 MCM
500 MCM
200 AMP**
Aluminum
250 MCM
250 MCM
300 MCM
600 MCM
900 MCM
200 AMP**

240 Volt, Conductor Size (AWG or kcmil) Single Phase, Max 3% Voltage Drop*

Length of Run

C/A
25'
50'
100'
150'
200'
AMP
Aluminum
4
4
4
4
2
50 AMP**
Copper
14
14
12
10
10
15 AMP**
Copper
12
12
12
10
8
20 AMP**
Copper
10
10
10
8
6
30 AMP**
Aluminum
8
8
8
6
4
30 AMP**
Copper
8
8
8
6
4
40 AMP**
Aluminum
6
6
6
4
3
40 AMP**
Copper
6
6
6
6
4
50 AMP**

*The tables assume steel conduit, a power factor of 0.9, an ambient temperature of 86°F, and no more than 3 current-carrying conductors. We have taken reasonable care to establish the accuracy of these values; however, this tool is intended only as a guide, consult a professional engineer to determine suitability for your application.
**Based on 60°C per NEC 110.14(c)(1)(a).
***Based on 75°C per NEC 110.14(c)(1)(b).

 

WARNING! Installation of electrical wire can be hazardous if done improperly, and can result in personal injury or property damage. For safe wiring practices, consult the National Electrical Code®, your local building inspector, or a qualified electrician.

Ampacity Calculator

Simplify complex wire ampacity calculations with FRCABLE’s convenient Online Ampacity Calculator. This intuitive calculator takes the guesswork out of electrical code compliance, ensuring you select the right conductor size for your specific application.

bottom of page