## Sizing Electrical Wire for Hot Water Heaters
### Determining Electrical Requirements
Before selecting the appropriate wire size for a hot water heater, it is essential to determine its electrical requirements:
– Voltage: Typically 120 or 240 volts
– Amperage: The current drawn by the heater, which varies depending on its wattage
– Wattage: The power consumption of the heater, measured in watts
### National Electrical Code (NEC) Guidelines
The National Electrical Code (NEC) provides guidelines for sizing electrical wire based on voltage, amperage, and insulation type. The NEC table below lists the minimum wire gauge for various amperage ratings:
| Amperage | 120V Copper Wire | 240V Copper Wire |
|—|—|—|
| 15 | 14 AWG | 12 AWG |
| 20 | 12 AWG | 10 AWG |
| 30 | 10 AWG | 8 AWG |
| 40 | 8 AWG | 6 AWG |
| 50 | 6 AWG | 4 AWG |
| 60 | 4 AWG | 3 AWG |
| 70 | 3 AWG | 2 AWG |
| 80 | 2 AWG | 1 AWG |
| 90 | 1 AWG | 1/0 AWG |
| 100 | 1/0 AWG | 2/0 AWG |
### Calculating Amperage
The amperage of a hot water heater can be calculated using the following formulas:
– For 120V heaters: Amperage = Wattage / 120
– For 240V heaters: Amperage = Wattage / 240
### Selecting Wire Gauge
Based on the voltage and amperage of the hot water heater, refer to the NEC table to determine the minimum wire gauge required. Consider the following:
– Always use the next larger wire gauge if the amperage rating is close to the maximum for a given wire size.
– For long wire runs (over 50 feet), consider using a larger wire gauge to minimize voltage drop.
– Use only copper wire for hot water heater installations.
### Recommended Wire Sizes
For typical hot water heater installations, the following wire sizes are recommended:
– 120V, 15-ampere heaters: 14 AWG copper wire
– 120V, 20-ampere heaters: 12 AWG copper wire
– 240V, 30-ampere heaters: 10 AWG copper wire
– 240V, 40-ampere heaters: 8 AWG copper wire
### Additional Considerations
– Insulation: Use wire with THHN (high-heat-resistant nylon) insulation, which is suitable for temperatures up to 90°C.
– Conduit: If the wire is routed through walls, ceilings, or other concealed spaces, use non-metallic conduit to protect it from damage.
– Grounding: Ensure the hot water heater is properly grounded using a bare copper grounding wire.
– Circuit Protection: Install a circuit breaker or fuse of the appropriate size to protect the wire and heater from overcurrent.
### Example
Consider a 50-gallon electric hot water heater with a wattage of 4500 watts.
– Voltage: 120V
– Amperage: 4500W / 120V = 37.5A
– NEC Table: Amperage closest to 37.5A is 40A
– Recommended Wire Size: 8 AWG copper wire
Therefore, an 8 AWG copper wire with THHN insulation is appropriate for this hot water heater installation.