Wiring Connections for an Electric Water Heater

By Dave Rongey - Summary:

How to Wire a Water Heater, The Electrical Connections for a 240 Volt Electric Water Heater, Identify the circuit for the hot water heater and make sure it is turned off.

Wiring Connections for an Electric Water Heater

Electrical Question: I’m connecting an electric water heater to the electrical junction box.
A O.Smith 50 gal MFG 02 Water heater has a red and black wire.
The electrical junction box has red, black, white and ground.
Please give advise.

Background: Perry, a Handyman from El Mirage Arizona.
Additional Comments: great

Dave’s Reply:
Thanks for your electrical wiring question Perry.

How to Wire a Water Heater

Skill Level: Intermediate to Advanced.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester.
Estimated Time: Depends on the personal level experience and ability to work with tools and access to the wiring.
Precaution: Identify the water heater circuit, turn it OFF and then Tag it with a Note before performing any wiring.
Special Materials: Properly sized wire connectors and blank cover.

Electrical Connections for a 240 Volt Electric Water Heater

  • Identify the circuit for the hot water heater and make sure it is turned off.
  • If the incoming electrical circuit has a black, red, white and ground wire then the white or neutral wire is caped off and not connected unless your water heater requires a separate neutral wire.
  • The bare ground wire of the incoming circuit is bent into a clockwise hook shape and placed under the green ground screw and secured tightly. This screw is located inside the water heater junction box, or the water heater may have a green ground wire that may be used.
  • The typical 240 volt water heater has a red and black wire located in a junction box at the top of the water heater.
  • The incoming circuit wires and the water heater wires are normally black and red, and are splices or connected together, color to color using red or gray wire nuts.
  • If the incoming electrical circuit wiring does not have a separate red wire, then the white wire may be used as the second 120 volt circuit of the 2-pole 240 volt circuit, and should be indicated with a black or red wrap of electrical tape of permanent marker. If unsure about the incoming circuit then the circuit should be verified by an electrician with a voltage tester.

The Following resources will assist you with your electrical question:

Electrical Junction Boxes
Electrical Code for How Many Wires in Junction Boxes

Electrical Wire for the Home

For more information about 220 Volt Wiring Diagram
220 Volt Wiring Diagram

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FAQs Frequently Asked Questions and Comments

8 Responses to “Wiring Connections for an Electric Water Heater”
  1. Dave Rongey says:

    Hi Tom,
    Most conventional electric water heaters have a built in junction box located in the top of the unit. At the point of connection, there is typically a knock-out opening where a flex conduit with the circuit wiring may be attached directly to the water heater. Therefore, a junction box is not necessary. However a junction box may be installed where the circuit wiring is located at the water heater which will enable you to transition to the flex conduit which will then attach to the water heater.
    I hope this helps,

  2. Tom Naivar says:

    Does the connection to the top of the water heater need a plug or j-box or can it be wired directly to the water heater terminals? This is for new construction.
    Thank you

  3. Dave Rongey says:

    The comment asking why a neutral is not used for the 240 volt circuit of an electric water heater refers to the neutral wire being used as the return path of the electrical current. This may be true in the case of a 120 volt circuit, however a 240 volt water heater does not need a neutral wire because the heating elements are 240 volts. Unlike a new electric dryer for example, which has a 120 volt control timer, an electric water heater does not yet have 120 volt controls. The 240 volt heating elements of the water heater are similar to most kitchen ranges and cook tops which have 240 volt heating elements which do not require a neutral wire as well. The thermostat controls for most of these types of devices control the temperature by making or breaking one leg of the 240 volt circuit. A simple explanation of power generation of Alternating Current, or AC Power, is that each leg of electrical power that is being produced is out of phase compared to each other leg of the power being generated.
    I hope this helps,

  4. Dave Rongey says:

    Hi Miguel,
    The wiring at the wall should be verified to make sure that they belong to a dedicated circuit which is designated for a water heater.
    Even though there is a typical 30 amp 240 volt water heater circuit that is installed in many homes, it should be noted that all electric water heaters are not the same and some will have specific circuit requirements, therefore you should verify the circuit requirements of your water heater and then compare the specifications to the circuit wiring which you have described to make sure the circuit is fully compatible.
    Note: Many of the older 30 amp 240 volt dedicated water heater circuits consisted of a 2-wire with ground cable, which consisted of a ground wire, a black wire, and a white wire, and in these circuits the white wire was normally connected to the red wire of a 240 volt water heater, however as described in the preceding, the circuit must be positively verified first. In newer installations where there is a 2-wire with ground cable for a 240 volt water heater the white wire is colored with red electrical tape which clearly designates it’s part of the 240 volt circuit. Identifying the circuit wiring with red electrical tape is important and should be applied to existing circuit wiring as needed.
    I hope this helps,

  5. Miguel Aviles says:

    I have 3 wires coming out of my wall: a bare copper wire, a white wire, and a black wire. my water heater has 3 wires colors which are a red wire, a green wire, and a black wire, what connects with what?

  6. Karl bethke says:

    I have an old basmore electric water heater. There are four wires that run into the control section of the water heater from the junction box on the heater. Two of these go to the top terminals on high temp cutout of the thermostat. The third goes directly to one side of the upper element. The fourth goes directly to one side of the lower element. The upper thermostat is faulty, but I can find a replacement that is exactly the same. And all the wiring diagrams I can find do not have these third and fourth wires going directly to the elements. Anyone have any advice?

  7. Steven Jarris says:

    I have been seeing that the water heaters are super important. It is also important how they are installed. I love to see these things. Keep up the great posts!

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