Do you have a new water heater? Are you thinking about wiring it yourself? You need wires of the right size. The wrong size could start a fire.
What Size Wire Do I Need For My Hot Water Heater?
In terms of Amperage
| Amperage | Wire Size |
| 20A | 12 Gauge |
| 25A | 10 Gauge |
| 30A | 8 Gauge |
| 50A | 8 Gauge |
| 60A | 6 Gauge |
In terms of Wattage
| Watt | Wire Size |
| 2000W | 10 Gauge |
| 2500W | 8 Gauge |
| 3000W | 6 Gauge |
| 3500W | 6 Gauge |
| 3800W | 4 Gauge |
| 4500W | 4 Gauge |
| 4800W | 3 Gauge |
| 3KW | 6 Gauge |
In Terms Of Gallon
| Gallon | Wire Size |
| 30 Gallon | 12 Gauge |
| 40 Gallon | 12 Gauge |
| 50 Gallon | 6 Gauge |
| 80 Gallon | 6 Gauge |
Wire Size For Tankless Water Heater
| Watt | Wire Size |
| 7600W | 4 Gauge |
| 9600W | 3 Gauge |
| 11500W | 2 Gauge |
| 13400W | 1 Gauge |
The greater the amp rating, the thicker the wire.
Most electrical professionals follow this scheme. They will only use 6-gauge wire once the water heater’s amp rating exceeds 50A.
How Do I Find Out What Size Wire Is Best For My Water Heater?
To calculate the precise wire size, you need the amperage. For instance, if you have a 3,000W heater that runs on 120V. According to the 80% rule, the amperage is (3000/120)*1.25 which gives you 31.25 amps. Based upon the amperage chart, the best wire size 3000W heater is 8 Gauge.
You also have to take these factors into account.
1). Voltage
Most water heaters use 220-250V. They use a double circuit breaker. Because the voltage requirements of most electric water heaters are the same, you don’t have to pay as much attention to the voltage as you do the amperage.
| Voltage | Wire Size |
| 220V | 10-2 Gauge |
| 240V | 10-2 Gauge |
2). Wattage
The wattage tells you the amount of electricity the water heater uses. However, you cannot use the wattage of a water heater to determine the size of the wire. You need the amperage.
3). Breaker Size
Technically speaking, you don’t need to know the breaker size to calculate the water heater wire size.
Once you have the voltage of your circuit and the wattage of the heater, you can find the amperage which, in turn, reveals the wire size. However, the breaker size is just as important.
First of all, if you add a water heater to a breaker with a smaller size, the breaker will keep tripping, which is annoying. If the breaker is too large, it won’t respond to short circuits or overloads. The size of the breaker is vital.
Secondly, wiring that matches the size of the breaker will most likely meet the needs of the water heater. For instance, using the example above, once you identify your water heater’s amp rating (25A), you should multiply that figure by 125 percent to stay in line with NEC regulations.
This will give you 31 amps. To select the right breaker, aim for a size that is closest to 31 amps. The obvious answer is a 35A breaker. Therefore, a 25A water heater requires a 35A breaker. A 35A breaker requires an 8-gauge wire.
4). Gallons
If you’ve ever gone water heater shopping, you know that the size of the water heater tank will influence the cost of the water heater. You also know that many contractors use gallons to determine the wire size.
A 40-gallon heater requires 12-gauge wire. On the other hand, you need 6-gauge wire for a 50-gallon water heater.
Like the amperage rating, the bigger the tank size, the thicker the wire. However, you don’t have to rely on the gallons to find the wire size. In fact, if your heater has a label that shows the wattage, you can ignore the gallons.
For instance, the typical 40-gallon heater has a wattage of 2500. This gives you an amp rating of 18.75 (2500 divided by 240). Because a 20A water heater uses 12-gauge wire, you can use 12-gauge wire on an 18.75A unit.
What Kind Of Wire Should I Use?
You need metallic cables with shielding. Pay attention to the gauge and its relationship to the distance. Most people know that a higher amp rating requires a thicker wire with a smaller gauge. They do not realize that the thickness of the wire should also increase as the distance increases.
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How Many Wires Does A Water Heater Need?
A water heater requires a black wire, white wire, and a ground wire. With a 10-2 ground shielded cable, white and black wires act as hot conductors. The ground wire will run to the neutral plug. If you have a 10-3 ground shielded cable with an extra conductor, the black and red wires are the hot conductors.
Why Does Wire Size Matter For My Hot Water Heater?
A wire that is too small (higher gauge number) is more likely to melt, starting a fire. This is because the water heater will force the wire to carry more electricity than it can withstand. This will lead to overheating.
Keep in mind that a smaller diameter translates into a higher resistance. And the more resistance a wire has, the more heat it will generate.
Where the gauge is concerned, the higher the number, the smaller the wire. The lower the number, the larger the wire. For instance, a 6-gauge wire is thicker than a 10-gauge wire.
Larger wires are not a problem. It is better to use larger wires than smaller ones. Unless you wired your circuit poorly, a larger wire is unlikely to attract significant consequences. Though, the cost is going to rise.
If you did not know, thicker wires cost more than their thinner counterparts. To avoid unnecessary expenses, and to prevent potentially fatal fires, use the right wire size for your heater’s wattage.
Does A Hot Water Heater Have To Be Hardwired?
It doesn’t have to be hardwired. An electric water heater requires a dedicated 240V circuit. Depending on the wattage of your heater, you can probably add it to a 30A double pole breaker.
You don’t have to hardwire your water heater to meet these basic requirements. Many people assume that a water heater must be hardwired because that is all they see.
They are convinced that cord and plug water heaters are dangerous because the water heater will eventually overload either the power cord or the wall outlet. But that isn’t true.
- First of all, cord and plug water heaters are quite common. It depends on where you live.
- Secondly, they are normally smaller and less powerful.
- Third, the power cords of the cord and plug water heaters are installed by the manufacturer at the factory. They are thick enough to meet the electrical demands of the heater without overheating.
- Fourth, you don’t have to worry about overloading the outlet if the heater is connected to a dedicated circuit. It should be the only appliance on that circuit. You can dissuade other people from connecting additional devices to the circuit by making the water heater’s outlet the only outlet on the circuit.
If the circuit has other outlets, you can apply tape to the slots to prevent other people from using them.
What Does The NEC Say About It?
1). The NEC categorizes fixed-storage water heaters as continuous loads.
2). They require controls with temperature limiting functions
3). According to NECA, the circuit rating should be at least 125 percent of the heater’s amp rating.
4). The NEC expects consumers to use 10/2 conductors for 4500W heaters.
Check your local fire and electrical code. If it specifies the wire sizes you should use for water heaters of particular ratings, you should listen.
Can I Use 10 3 Wire For A Hot Water Heater?
You can use 10/3 wire. Use the red and black wires as hot conductors. The ground wire will run to the green screw. Cap the white wire off. Your electrician won’t buy 10/3 wire for your heater. But if you already bought one, they can make it work.
Can I Use 10-2 Wire For A Water Heater?
You can use a 10/2 cable (with a ground wire). It is the most common type of cable that electricians use to wire water heaters. A 10/2 cable has two conductors. It is perfect for 30A breakers.
Can You Use 12 2 Wire For A Water Heater?
There is nothing wrong with using 12/2 wires. But I suggest you use 10/2 cables. Even if you have a smaller heater with a lower wattage, 10/2 wires give you the option of upgrading your water heater in the future.
It saves you from the trouble of replacing the wires the next time you decide to buy a larger, more powerful unit.