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Want to add a 12A under sink water heater, but the only nearby power is a switched outlet that currently runs the garbage disposal (1/2hp, ave draw ~7A, but I assume more at startup). This outlet is on a dedicated 15A circuit, but if both the heater and disposal happen to be on at the same time, it will exceed the capacity. What about replacing the single pole switch (that controls the outlet of interest) with a 3 way switch, running 3 wire cable between switch and outlet, and wiring each half of the outlet separately (of course, breaking the tab that connects the two sides)? Meaning, with switch in down position, only one side of outlet is hot, with switch in up position, only the other side is hot. So, if the disposal is switched on, the receptacle used for the water heater would be switched off. Would this functionally work? Meet code? Any better suggestion that does not involve running a new dedicated circuit for the heater? Thanks

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    Your idea would work but is it acceptable in your area. In my area water heaters are required to have their own branch circuit. What jurisdiction are you located in? Is there any reason you cannot pull in a second circuit?
    – Gil
    Feb 5, 2022 at 19:00
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    Will the water heater require a local disconnect switch? (if it connects with a plug, the answer is "no"). Feb 5, 2022 at 19:08

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I don't really see a problem since the circuit serves only one or the other and the tanked heater doesn't mind interruption. But some inspectors might kick a fuss about the line not being dedicated.

My only concern is the switch, a garden variety 89 cent 3-way switch isn't exactly rated for 12A of partially motor load.

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Code applies to the hard wired section, and changes to the permanent wiring of the home. If you added a cord connected 3 way switch, you'd not need a permit for your scheme.

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  • Different countries have the different rules.
    – user263983
    Feb 5, 2022 at 21:27

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