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How to Wire a Hot Water Heater to Breaker Box in 8 Steps

Written by Edwin Jones / Fact checked by Andrew Wright

how to wire a hot water heater to breaker box

Are you noticing that your water heater starts to build up rust in crucial areas of your tank? Do the visible signs of wear and tear affect your heater’s performance? If yes, then you need to replace the device immediately.

Learning how to wire a hot water heater to breaker box requires simple skills. Mostly you’ll need to execute neat wirings when connecting your hot wires and ground wire to their corresponding places in your heater and designated circuit breaker.

However, if you’re not comfortable working around pipelines or electricity, please leave the responsibility to a professional plumber or electrical contractor.


What You Will Need


Assuming you already purchased your electric water heater replacement, acquiring the rest of the materials will not be a problem. Comply with the list below before wiring electric water heater and make sure you have the correct sizes.

1. Circuit breaker


When water heaters deteriorate or a new water heater’s amperage requirement changes, it is essential that you replace your breaker. A conventional 30-40-gallon water heater matches with a 30 or 40-amp feed.

30-amps is the usual choice of most homeowners for their boiler tanks because it can handle the ampacity of a water heater, including its maximum continuous load. Nonetheless, recheck the specs of your substitute heater to avoid a mismatch with your breaker.

2. Electrical wires


Same as the breaker, all wirings for your water heater should match with all of its components and safety device. Since the generic breaker size for water heaters is 30-amps, the best wire size is a #10 American Wiring Gauge (AWG).

I suggest you use a 10-2 Non-Metallic Cable (NMC) for a 30-amp 240Volt circuit. This type of wire consists of two conductors with a ground— a total of three wires.

A pro tip for you: The wire that connects a water heater to a panel is often a Romex 10/2 cable. It has black wire, white wire, and copper wire. Although white wires are usually neutral, the white Romex wire is actually a hot wire. Before starting the work, I highly advise you to mark that wire with tape to remember it is a conductor.

3. Voltage tester


As a DIY guy who has little knowledge of how to wire hot water heater, you should be responsible for your safety.

A voltage tester or meter is an excellent help for protecting yourself from accidents like touching a live wire unknowingly. It will alert you with a simple flashing bulb method: green light for “no current” and red light for “live wire.”

With this device plus body insulation like rubber gloves and boots, you’re ready to go.

Steps on Wiring Your Water Heater to Breaker Box


Now that you successfully gathered all your tools, proceed with wiring hot water heater to the breaker box. Again, if you are not sure about what you’re working on, it is better to pay a few bucks on a professional rather than risking your life or your family’s.

Step 1: Shut off the primary sources


As all electrical maintenance should be, shutting down the main source of electricity is the primary step. This procedure is necessary for getting a free hand on the wires without the risk of electrical hazards. On the other hand, to conserve water, turn off the crank of the main pipe that supplies your home.

Step 2: Drain the excess water and depressurize

Once you get the running water out of the way, it is time to remove the pressure from your pipes. Open one or two faucets and let all the remaining water inside the pipelines drain. As you do this, do not forget to drain pipes of both temperatures, hot and cold. Let them run for a few minutes.

Step 3: Install the circuit breaker


Before installing the dedicated CB for your electric water heater, grab your voltage tester and ensure everything’s offline. No power should be available from every bus bar to the wiring screws, with your voltage tester indicating a green light. When you’re free to go, carefully attach the breaker to the bus bar until you hear a click.

Step 4: Run the wiring


Plan how you want to run your wirings from the breaker box to your Electrical Metallic Tubing (EMT) or electrical flex connecting to the water tank. Neatly fasten your wires on the wall or at the ceiling (if needed) with a conduit fastener.

You can refer to an electric hot water heater wiring diagram to better understand the connection between your breaker and the heater. However, if the previous wirings are still okay, you can skip this procedure.

Step 5: Wire in the circuit breaker

Connect your 10 AWG wire to the breaker. Strip a small portion of the cables. Remember to leave an adequate length of wire and not cut all the way through. Start connecting the hot wires on both poles of the CB. Then, screw in the ground wire to its respective spot.

Step 6: Wire in the water heater

Fish the wires from the Electrical Metallic Tubing to the hole of your water heater’s junction box. Once you affix your wires through the junction cover, strip the insulation for about .75 mm. Get your wires through the ROMEX connector & clamp the NM cable’s sheathe.

Connect the ground wire to the ground screw inside the junction box. Twist the black wire of your circuit around a water heater wire (you can pick any wire you want). Use a wire nut to seal them up. Find your panel’s white wire & mark it with tape (to signify its status as a hot wire). Afterward, link this white wire to another wire of the water heater.

Step 7: Open the main pipe and fill the tank

Ensure that everything is sealed, from the PVC pipes to the wiring lines, inside or outside the junction box. Turn the water source on and fill up the tank first before switching on the electrical heating element. Then, depressurize the pipes by letting all your faucets run for three minutes.

Step 8: Turn on the main breaker box


Switch on the main electrical panel and the dedicated circuit breaker for the water heater. For safety measures, use the voltage tester to locate any electrical leaks outside your tank. Checking includes metal parts like junction covers and screws.

For a few reminders, always check the tank’s water heating element, top, and bottom. In a worst-case scenario where frozen pipes occur, the heating element will run even with a depleted water source. This neglect results in damage due to overheating. If you need a replacement, make sure everything’s the same as the previous setup.


Did you have fun reading this tutorial? Knowing how to wire a hot water heater to breaker box is not as complicated as you think. Match the breaker and wiring sizes to the electrical information of your tank, and you’ll be fine. I’ll repeat, if you are not comfortable wiring electrical or doing plumbing work, call your trusted contractor ASAP.

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