Build my own cabin - DIY projects

How to Wire a Water Heater

The first step in how to wire a water heater is to make sure you have proper electrical power to the water heater. Electric hot water heaters typically require a dedicated 30-amp, 240-volt breaker.  The wire supplying power from the breaker panel to your water heater will usually be a 10/2 Romex cable (Blk wire- hot, Marked White wire - hot, Bare copper wire - ground). Since a water heater has no outlet, the cable will be run from the wall to the junction box on the water heater.   Any cable that comes out through a wall through the sheetrock should be encased in flex conduit (BX cable) or wire loom and fastened at each end from the wall to the appliance with cable fasteners or grommets.

Note: Do not fill up the tank with water until the water heater is wired up and then, do not turn on the circuit until the tank is filled with water.  There have been many cases of folks who do not know how to wire a water heater apply power to the tank without water, the electric element quickly over-heats and opens up, and then they are trying to figure out what they did wrong.

Inside electric water heater       

  1. If you are replacing an electric water heater, your wiring should already be present at the site.  If you are changing to electric from a gas unit, you will need to wire a dedicated 30-amp circuit and 12-2 Romex to the site of your water heater.
  2. On the top or the side of the water heater you will see the junction box cover where the electric connections are made.  Remove the screw and cover.  Inside you should see two lead wires and a ground screw.
  3. Remove the knockout on the junction box and attach your flex conduit with about 6 inches of wire sticking inside the box.  Do not let the flex conduit come in contact with the water pipes. Doing so can transfer heat from the hot water pipe to your conduit - wires do not like that extra heat.


  1. Inside the junction box, wrap the ground wire around the ground screw and tighten down securely.  Next, take the black wire from the feed circuit and one wire from the water heater (it doesn't matter which wire) and twist them together.  Secure them with a wire nut.  With the white feed wire coming from the panel, wrap electrical tape over its insulation to identify it as a current-carrying line (the same should be done at the breaker panel as well where the white wire ties into the second hot pole of the 240V breaker rather than the neutral bus). Once it's marked, connect the white wire to the other wire in the water heater just as you did the black wire.
    Note: Since the hot water heater is a 240-V appliance, it does not require a neutral wire.  Thus, the white wire is actually a "hot" line in this application.
  2. The last step in how to wire a water heater is to replace the junction box cover.  Turn on the water supply and fill the tank with water.  Once fully filled with water, turn the circuit breaker back on.  Without water in the tank when you turn it on, the heater element can quickly overheat and be damaged.


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