electric water heater wired from j box
You need a disconnect on an electric water heater. That means you can use the box you have, but you will need a 30 amp, two pole, single throw switch and switch plate. You must access the box cable openings for the power in and power out to the heater.
If it where me I would abandon the box you have and pull the cable out of it. Put a blank plate on it. Then take the cable and install a cheap AC disconnect. The disconnect will be less money than the switch mentioned above. Just run another length of cable from the disconnect to the water heater. Route it so it is not subject to physical damage. You will need three NM connectors, anchors for the disco, red wire nuts and about an hour of your time.
Last edited by J. V.; 09-24-2009 at 01:03 PM.