10 2 or 10 3 Wire for Water Heater? [The Right Choice!]

Maybe you’ve got a new water heater and have to wire it. But, not all wires are the right choice for your heater. 

So, which one is preferred between 10 2 or 10 3 wire for water heater?

Generally, water heaters with higher capacity need 10 3 wires. On the other hand, lower circuits with 3 prong outlets need 10 2 wires to operate. Whether to use 10 2 or 10 3 wire depends on the water heater itself. 

Thus, read our whole article to know more about it. 

10/2 And 10/3 Wires- The Right One for Your Water Heater!

Both 10/2 and 10/3 wires have different features. First, let’s look at them:

Now, let’s describe these features in detail.

When Can You Use 10/2 Wires for Water Heater?

Normally, lower voltage (Usually 240V) 3-prong water heaters are the best fit for 10/2 wires. Now if you think about the amp rate then a water heater of 30 amp or lower circuit will be the best suit for it.

10/2 wires are frequently used in residential circuits and appliances. Here, the number 10 in 10/2 represents the size of the wire. It represents AWG (American Wire Gauge)

which holds a certain diameter. Usually, 10 AWG wires have a diameter of 2.58 mm. 

10 AWG wires with this diameter can support about 30-35 amps. Though, they are mostly used for circuits under 220V. Lower circuits with 110V with 30 amps are ideal for 10/2 wires. That means you can also use 10/2 wires on a heater of 110V, 30

Source: wirewireelectricsupply.com

Now, the number 2 in 10/2 represents the number of live wires. In 10/2 wires, there are two live wires which are hot and neutral. Another wire is used as ground. The ground wire is either green or bare copper. The hot wire is black and the neutral is white.

Source: nickleelectrical.com

Since they have three wires, the outlets designed for them are also 3 pronged. Although they’re used for 30 amp and 240V water heaters in some cases. In that case, the 10/2 wires are double pole breakers. Thus, they can handle higher voltage applications. 

When Can You Use 10/3 Wires for Water Heater?

In comparison, 10/3 wires are better than 10/2 wires. These types of wires are better fit to support a high-voltage circuit. Thus, more than 220V water heaters with 30-35 amps (Sometimes even 40 amps) are mostly wired using 10/3 wires. They’re commonly used in electric tank-type water heaters. 

10/3 wires are also used for home appliances but with higher current needs. Here, also  the wire is of the same size.  Thus, it has the same diameter and amperage rating. Here, the main difference is in the number of live wires.

The number 3 in 10/3 represents that the wire has three live wires. Here, two wires are hot and one is neutral. The other wire is ground.  

Here you should also know which gfci breaker to use for tankless water heaters.

Are 10/2 and 10/3 Wires Interchangeable? 

Yes, 10/2 and 10/3 wires are interchangeable only for a certain range and system. As we know, the amperage for both wires is 30-35A. But, the voltage requirements are different. Thus, the load will be different too. 

For 10/3 wires,

Load= 30-35A * 220-240V= 6600-8400W≈ 6500-8500W

For 10/2 wires, 

Load= 30-35A * 110-200V= 3300-7000W≈ 3000-7000W

Here, we can see that the 6500-7000W range is present in both the wires. Thus, technically both wires should be able to handle this load. But, even if this wattage matches, heaters are built with a certain wiring system. 

If your heater’s capacity is 7000W, both wires should work. In fact, 10/3 wires are recommended as it’s near the maximum range of 10/2. Using 10/2 wires might be detrimental. But, if the heater has a 3-wire system, you’ll just have to use 10/2 wires. 

How to Wire My Water Heater

Now that you know which wire to use, let’s see how you can wire the heater.

Using 10/2 Wire:

For a heater that uses a 3-prong outlet, 10/2 wires are used. Just follow these steps to wire them. You can also look at our instructions for wiring 240V wall heaters.

Precaution: Before starting to work, make sure the power lead has no power. Take a multimeter and test the power lead for voltage. Make sure the voltage reading is 0. Now, you can start working. 

Step 1: Using a screwdriver, remove the panels which cover the water heater. The three wires should come out. Put the screws of the panel somewhere safe.

Source: youtube.com

Step 2: Now, take your electric adapter and put it through your power lead.

Source: youtube.com

Step 3: Now, take the panel side which has a hole in it. Put it through the cables to the electric adapter. Next, take the nut and put it in too. Tighten the nut with the panel. 

Step 4: Now, bend the wires of the power lead. Put the panel where it was attached to the heater and screw it in.

Source: youtube.com

Step 5: Now, you’ll have to attach the wires of the power lead and the heater.  Attach the live wires of the heater and the power lead. It doesn’t matter which one you attach when it’s the live wires. Lastly, attach the ground wires using wire nuts.

Source: youtube.com

Step 6: Now, bend them down and tuck them in the compartment. 

Step 7: Now, take the ground wire of the power lead. If it’s too long, cut it a little. Then, bend the wire under the grounding screw and screw it in.

Source: youtube.com

Step 8: Lastly, attach the other panel by screwing it in.

With that, the wiring has been done. If you make a mistake while wiring, the water heater will malfunction. But, malfunctions like water heater leaking when the washing machine is on are different.

Using 10/3 Wire:

If your heater has a four-prong outlet, it uses a 10/3 wire. The process will be almost the same here. While wiring, you’ll just have to attach three of the live wires. Again, using wire nuts, attach the wires of the power lead to the heater.  

Frequently Asked Questions (FAQs):

How to Measure Wire Size?

You can measure the wire size with AWG. For example, if the AWG of the wire is 10, its diameter will be about 2.58 mm. You can look at the insulation of the cable for texts. The last numbers of the text strings will be your AWG. Now, look up the AWG converting chart for the diameter of the wire.

What is a 4mm 2 Core Cable Used for? 

4 mm 2 core cables are used to supply the main voltage current. These cables are usually armored. Thus, they’re perfect for underground installations. They’re also attached to building structures with cable cleats. They’re most commonly used for gardens, security, factory lighting, and electric gates. 

Is it Ok to Install Your Own Water Heater?

It’s ok to install your own water if you have the necessary skills and confidence. But, if you are not confident with DIY projects, it’s better to hire a professional. 

Bottom Line!

We hope you got to know everything about 10 2 or 10 3 wire for water heater. Still, we have one last tip for you. Always check the AWG table for how many amps your wire can support before using it. Thanks for sticking with us till the end.