What Size Wire for Water Heater? — Complete Wiring Guide
A Water Heater requires 10 AWG copper with a 30A double-pole on a 240V dedicated circuit. Here is the complete NEC-compliant wiring guide.
Water Heater Wiring Details
A standard 4,500W electric water heater draws 18.75 amps at 240V. Since water heaters run for extended periods during recovery, NEC classifies them as continuous loads requiring a circuit rated at 125% of the load: 18.75A × 1.25 = 23.4A. This means a 30A breaker with 10 AWG copper wire. Use 10/2 NM-B (Romex) with ground for most residential installations. The cable runs from a dedicated 30A double-pole breaker in the panel directly to the water heater — no other devices share this circuit. Most water heaters are hardwired, not plugged in, using a cable whip or flexible conduit at the connection point.
NEC Code Reference
The wiring requirements for a Water Heater are governed by NEC 422.11(E). Always check the appliance nameplate for specific electrical requirements — the manufacturer's specifications take precedence over general guidelines. Your local AHJ (Authority Having Jurisdiction) may have additional requirements beyond the NEC.
Pro Tip
If your water heater is more than 50 feet from the panel, consider running 8 AWG wire to minimize voltage drop. A 3% voltage drop on a 50-foot run of 10 AWG at 18.75A equals about 4.3V — acceptable but not ideal. On longer runs, the reduced voltage can slow heating recovery time.
Disclaimer: This guide is for reference only. All electrical work must be performed by or verified by a licensed electrician. Local codes may differ from NEC.