How to Wire a Hot Water Heater Using a Wiring Diagram

Electric water heaters use wiring diagrams to plot the wire connections.

In most cases the limit switch and the thermostat share a plastic housing. Some water heaters use two thermostats and two elements to heat the water. For the water heater to work properly, both thermostats should have their temperatures set at the same level.

1. Find the sticker with the water heater's wiring diagram on it. Water heater manufacturers usually apply the sticker to the top of the water heater or on the side of the water heater next to the access panels.

2. Inspect and understand the wiring diagram before beginning. A rectangle made out of dotted lines represents the circuit breaker or fuse box. Solid lines represent the wires. Rectangles made out of solid lines represent the high-temperature limit switch, on top, and the thermostat, on bottom. The numbers on the rectangles represent the wire terminals; each terminal uses its own number. The circle under the rectangle represents the heating element. The ground wire uses the word "Ground" or "GND" and a series of small lines to identify itself.

3. Open the water heater's access panels with the correct screwdriver. Often manufacturers use Phillips-head or 1/4-inch hex-head screws to hold the access panels in place.

4. Strip 1/2 inch from each insulated wire from the wire set that leads to the circuit breaker. The wire set contains two insulated wires and an uninsulated wire.

5. Push the wire from the circuit breaker into the hole next to the access panel on top of the water heater. If the hole contains a wire clamp, then tighten the wire clamp's screws after inserting the wire, using a slotted screwdriver. Wire clamps use two slotted screws to bind a half-moon-shaped clamp against a wire.

6. Wrap the uninsulated wire from the circuit breaker around the water heater's ground screw and tighten the screw with the proper screwdriver. The ground screw connects to the water heater's outer housing.

7. Wrap the black-colored wire from the circuit breaker around the water heater's black-colored wire that leads to the high-temperature limit switch. Tie them together with a wire nut.

8. Wrap the white-colored wire from the circuit breaker around the water heater's red- or white-colored wire that leads to the high-temperature limit switch. Tie them together with a wire nut.

9. Connect the wires that lead to the circuit breaker's wires to the high-temperature limit switch. The black-colored wire connects to the terminal labeled "1" and the red- or white-colored wire connects to the terminal labeled "3." After connecting the wires, tighten the terminal screws with a Phillips-head screwdriver.

10. Connect a jumper between the high-temperature limit switch's "2" terminal and the thermostat's "1" terminal. If the manufacturer supplied a factory-installed metal jumper, skip this step. If not, cut a short piece of wire with wire cutters and strip both ends before securing the wire.

11. Connect a wire between the thermostat's "2" terminal and one of the top element's terminals. Connect a wire between the high-temperature limit switch's "4" terminal and the top element's second terminal. Tighten each screw with a Phillips-head screwdriver.

12. Supply electricity to the bottom thermostat and element, if equipped. Connect a wire between the high-temperature limit switch's "4" terminal and one of the bottom element's terminals. Connect a wire between the upper thermostat's "4" terminal and the lower thermostat's "1" terminal. Connect a wire between the bottom thermostat's "2" terminal and the element's second terminal. Tighten each screw with a Phillips-head screwdriver.