- Voltage drop becomes important when the length of a run of wire or cable becomes very long. Usually this is not a problem in circuits within a house, but may become an issue when running wire to an outbuilding, well pump, etc.
- Excessive voltage drop can cause loss of efficiency in operation of light, motors and appliances. This could result in lights that are dim and motors or appliances whose life is shortened.
- To avoid excessive voltage drop, select a size wire that will minimize voltage drop, You need to know the length of the wire run and the amp load or current that will be on the circuit. To determine amps, add up the wattage of all electrical devices that will be on the circuit and divide this total by the voltage of the circuit, 110 or 220
- Wire Size Selection for Long Runs
|
110 Volt, Single Phase, Max 3% Voltage Drop*
| ||||||
|---|---|---|---|---|---|---|
|
Length of Run
|
||||||
|
|
25'
|
50'
|
100'
|
150'
|
200'
|
|
|
Copper
|
14
|
12
|
8
|
6
|
6
|
15 AMP
|
|
Copper
|
12
|
10
|
8
|
6
|
4
|
20 AMP
|
|
Copper
|
10
|
8
|
6
|
4
|
3
|
30 AMP
|
|
Copper
|
3**
|
3**
|
1
|
2/0
|
3/0
|
100 AMP
|
|
Aluminum
|
2
|
2
|
2/0
|
4/0
|
300 MCM
|
100 AMP
|
|
Copper
|
3/0
|
3/0
|
3/0
|
250 MCM
|
350 MCM
|
200 AMP
|
|
Aluminum
|
4/0
|
4/0
|
300 MCM
|
400 MCM
|
600 MCM
|
200 AMP
|
|
220 Volt, Single Phase, Max 3% Voltage Drop*
| ||||||
|---|---|---|---|---|---|---|
|
Length of Run
|
||||||
|
|
25'
|
50'
|
100'
|
150'
|
200'
|
|
|
Copper
|
14
|
14
|
12
|
10
|
8
|
15 AMP
|
|
Copper
|
12
|
12
|
10
|
8
|
8
|
20 AMP
|
|
Copper
|
10
|
10
|
8
|
6
|
6
|
30 AMP
|
|
Aluminum
|
8
|
8
|
6
|
4
|
4
|
30 AMP
|
|
Copper
|
8
|
8
|
8
|
6
|
4
|
40 AMP
|
|
Aluminum
|
8
|
8
|
6
|
4
|
3
|
40 AMP
|
|
Copper
|
8***
|
8***
|
6
|
4
|
4
|
50 AMP
|
|
Aluminum
|
6
|
6
|
4
|
3
|
2
|
50 AMP
|
* The table above applies to the single phase systems, in steel conduit, at a conductor operating temperature of 75°C. It assumes a power factor of one. The table may be used for systems using non-steel conduit, but actual results for these conditions may result in a greater voltage drop.
** Type NMB cables may not be used for a 100 amp load.
*** Must use 6 gauge if using NMB or UFB.
WARNING! Installation of electrical wire can be hazardous, if done improperly, can result in personal injury or property damage. For safe wiring practices, consult the National Electrical Code® and your local building inspector.
