Wire gauge calculator for AC applications
Online single phase calculator for copper and aluminum wire sizes (AWG ) in AC applications to meet desired voltage drops based on wire type, length and voltage.
To find the minimum wire gauge, the supply voltage (v), load current(A) and one-way length of cable (feet) need to be provided to the calculator.
* wire length is the one way length of wire from the voltage source to the appliance
**Resistance values used are based on alternating-current resistance values for 600-Volt Cables, 3-Phase, 60 Hz, 75°C (167°F) — Three Single Conductors in Conduit. Resistance values assume a fully loaded conductor at that temperature. Resistance for conductors hence voltage drop at different temperatures, stranding may vary.
- What is the voltage drop for 4 gauge wire, carrying 15 amps over 200 feet at 120 V?
The voltage drop is 2% with a final voltage of 117.6 V (see screenshot below).
AC Voltage drop formula
The AC voltage drop for single phase can be found from the formula = I*R where:
- I is the alternating current flowing
- R is the alternating current resistance for the conductor based on NEC Table 9.
Causes, effects and prevention of voltage drop
Voltage drops results in wasted power along the cable run and a reduced voltage for the appliance which may cause the appliance not to work properly.
To ensure that your appliance receives its recommended minimum operating voltage, select a wire gauge and appliance location (cable length) such that the final voltage for the appliance meets your appliance voltage requirements (ideally not more than 3% for branch circuits).
Longer cable runs increase voltage drop
For example, at 120V, an appliance drawing 10A over 10 AWG wire, the one way cable length to the appliance can at 90 feet would result in a voltage drop of 2%.
Should this distance double (180 feet), then the voltage drop would double to 4% increasing the power wastage and may result in the appliance not working properly.
Fix: To maintain the voltage drop (2%) while maintaining the cable length, decrease the wire gauge to 6 AWG.
Large appliances increase voltage drops
Larger appliances (larger loads) require more current which results in a bigger voltage drop for the same distance.
Therefore to reduce the drop, you need to increase the size of wire, lower gauge.
At 120V, a 3% voltage drop results for a 10A load when using 12 AWG wire with one way distance for the load at 70ft.
If the load increases, drawing a current of 15A, to maintain the same wire gauge and 2% voltage drop, one way cable should be 61 feet.
- If this is not possible to move the load (reduce the cable length, you may use a thicker cable, 10AWG.
- Double the voltage to 240V if the load can take it which would allow you to extend the load up to 123 feet!.