How to Wire a Hot Water Heater

Did you know that the lifespan of an electric water heater is about 10-15 years? That means if you live in your house for a decade, you will probably have to replace it and connect wiring to the new unit. Installing an electric water heater is not that difficult of a task, and it's one you will repeat in life, so why not learn to do it yourself? Here you can learn how to wire a hot water heater without the help of a professional. Remember that when doing electrical work, safety is paramount. Do not take any risks, and if you are uncomfortable with what's required in this process, hire a professional. 240v of electricity is enough to kill a man.

diagram of components for learning how to wire a water heater

For general electrical safety tips, check out this helpful article.

How to Wire an Electric Water Heater

Before you get started, you need to ask yourself, is power currently running to the water heater's location? In cases where you are replacing a gas tank with an electric, you will likely need to run cable (2-pole, 30-amp breaker with 10-2NM cable) from the circuit to the tank. If the circuit breaker is already running a line to the water heater's location, you can proceed to step 1.

One last tip before we get started: do not fill the tank with water until the tank is completely wired, and do not turn the circuit on until the tank is full of water. The heating element will break if it's not submerged in water.

Wiring a Hot Water Heater in 7 Steps

  1. Remove the junction box cover - this is probably on the top or the side of the water heater. Likely, you will only need to remove one screw to uncover two lead wires and a ground screw.
  2. Test the voltage - never mess with any electrical components without first checking to see if there is power running to the appliance. If there is power there, it is called a "Live" circuit. Please be careful! Not only will you void the warranty while manipulating wiring when live, but it could very well result in personal injury. If You are uncertain whether you have a live circuit or not, it would be a good idea to use a voltage meter to check for power running to the lead wires. If you find there is power, interrupt it. You can do this by tripping the GFCI breaker in the plug, if available (push the "TEST" button located in the center of the outlet). If that's not an option, find the appropriate breaker at the power supply breaker box and switch it to the off position.
  3. Remove the knockout - you will find a knockout within the junction box. You can remove it with needlenose pliers.
  4. Strip the wire insulation - if you did run the cable yourself, you might have to remove the plastic sheath so that you can expose the wiring (you need about 6" to go within the junction box). Then strip about 0.75" of insulation from the individual wires.
  5. topside view of how to wire a water heater
  6. Fish the wiring - run the wires through the ROMEX connector, then tighten and clamp over the sheathed portion of the NM cable. You shouldn't be left with any exposed wires. Fish the wires through the knockout and then position the ROMEX connector permanently with a lock nut. Tip: you do not want the Romex connector to be touching water pipes. You don't want the temperature of the hot water outlet to compromise your electrical work.
  7. Connect the water heater to the circuit - back within the junction box, you will wrap the ground wire around the ground screw and secure it. Take the black wire from the circuit and any wire from the water heater and connect them (twist together and secure with a wire nut). Take the white wire ("hot" line) and wrap electrical tape over its insulation (this is for identification purposes). Do this at the breaker panel, too. Then connect the white wire with the other wire within the water heater.
  8. Replace the junction box cover - this is essentially the last step. Fill it with water and then turn the circuit breaker back on, and then you can run your new water heater.

Thanks for Choosing the Plumbing Experts

We appreciate you visiting us here at If you have any questions about your water heater wiring project, please contact us. Remember, we carry trusted names, like Bradford White, Takagi, Stiebel Eltron, etc. Shop around for replacement parts, as well as water heater accessories.

Related resources:
How to Install a Gas Water Heater
Installing an Electric Water Heater
How to Solder Water Heater Pipes
How to Install a Water Heater Expansion Tank

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