Table of Contents
220V Wire Sizing Basics
220/240 volt circuits are used for high-power appliances like electric dryers, ranges, water heaters, air conditioners, and EV chargers. These circuits carry significant current and require properly sized conductors to prevent overheating and excessive voltage drop. Most residential 240V circuits use two hot conductors, a neutral, and a ground wire.
The advantage of 240V over 120V is that for the same power, the current is halved, which means smaller wire can be used. However, the distances involved in some installations, such as detached garages or outbuildings, can still require substantial wire gauges to maintain acceptable voltage drop levels.
Wire Size Formula
Where CM is circular mils needed, K is 10.37 for copper or 17.02 for aluminum, I is current in amps, D is one-way distance in feet, and VD is the maximum allowed voltage drop. For 240V at 3%, the allowed drop is 7.2 volts.
220V Circuit Wire Table
| Circuit Amps | Copper AWG | Aluminum AWG | Typical Use |
|---|---|---|---|
| 20A | 12 | 10 | Window AC, power tools |
| 30A | 10 | 8 | Dryer, small water heater |
| 40A | 8 | 6 | Range, large water heater |
| 50A | 6 | 4 | Range, EV charger (Level 2) |
| 60A | 4 | 3 | Sub-panel feeder |
Frequently Asked Questions
What size wire for a 30-amp 240V dryer?
A 30-amp 240V dryer circuit requires 10 AWG copper wire for runs up to about 50 feet. For longer runs, you may need to upsize to 8 AWG to keep voltage drop under 3%. Most dryer circuits use 10/3 NM-B cable with ground.
Can I use aluminum wire for 240V circuits?
Yes, aluminum is commonly used for larger 240V feeders because it is lighter and cheaper than copper. However, all connections must use anti-oxidant compound and be rated for aluminum conductors. Use wire two sizes larger than copper equivalents for the same ampacity.
What is the difference between 220V and 240V?
In the US, the nominal voltage is 240V split-phase, though it is often colloquially called 220V. Actual measured voltage typically ranges from 228V to 252V depending on utility conditions and distance from the transformer. Wire sizing calculations should use the nominal 240V value.