Installation Details for Electric Water Heaters
First turn off the power to the water heater at your main electrical panel. Then follow the same draining procedures as for a gas water heater.
When the water heater is drained, disconnect the electrical wires from the screw terminals under the access panel, which is usually located near the top. (If you don't have electrical experience, hire an electrician to handle all the electrical wiring.)
Follow the manufacturer's instructions for wiring the new water heater. If the new water heater is shorter and the old wires won't reach, surface-mount a 4-in. x 4-in. x 1-1/2 in. metal electrical box on the wall or ceiling nearby, run the old wires to the box, and then run a new section of armored cable or electrical conduit to the water heater. Check the instructions and make sure the rating of the old fuse or circuit breaker is high enough to handle the new water heater. In addition, the circuit should have a shutoff switch within sight of the water heater.
Call your local electrical inspector before you begin the job. You'll probably need a permit. Then, when you're finished, have the electrical inspector check your work.
CAUTION: Aluminum wiring requires special handling. If you have aluminum wiring, call in a licensed pro who's certified to work with it. This wiring is dull gray, not the dull orange that's characteristic of copper.