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Current setup:

  • An old, hardwired, garbage disposal
  • Controlled by a wall switch
  • 20A breaker for disposal

I am replacing my garbage disposal and also wanted to add an instant hot water dispenser, but I don't have anywhere to plug it in under the sink.

My idea:

Note: My dishwasher is separately hard-wired behind the dishwasher (not sink cabinet) so using that seemed harder.

Questions:

  • Is it okay to have both the disposal and the instant hot water dispenser on the same breaker/wiring?
  • Any issues with my plan overall?
  • You want your disposal switch to be far enough away so you can't turn it on when your hand is in the disposal (removing a spoon or bone or whatever). – Mattman944 2 days ago
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    @Mattman944: Yet in practice, this is rarely done. I sympathize with the sentiment. But consider the scenario where the switch is further away than you can reach from the sink. That doesn’t stop somebody else from reaching it. And if somebody else turns it on, well, you can’t reach it from the sink to quickly turn it back off. – Craig 2 days ago
  • That pushbutton is cheap Cheese junk. It's right off Alibaba. Since the unit isn't even properly UL-listed, it's not legal to install actually. Best to avoid Amazon like the plague for safety or electrical gear. Even if it says "Sold By amazon.com" like the dispenser does, counterfeits still slip in due to Amazon commingling. – Harper - Reinstate Monica 2 days ago
  • Thanks. I haven't bought the switch yet so open to others. I see homedepot.com/p/… as an option. Interestingly from the reviews it seems like it actually temp cuts off power to the hot water heater while disposal is on, which seems like it would alleviate the power concern. – philfreo 2 days ago
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The main rules that I am aware of (but I am not a professional electrician) are:

  • Total planned usage should be < 100% of total and < 80% continuous usage

With a 20A circuit, 80% = 16A. 15.75A < 16A, so you're good there. Actually, the disposal would likely not count as continuous anyway, but since the numbers work, no problem.

  • If hardwired loads are > 50% of the capacity of the circuit, then you should not have any receptacles for plug-in loads.

This is where you could get to a problem. 9.5A is under 50% of the total, but more than 50% if rated at 80% for a continuous load. I don't think that is a problem. It is certainly not a problem if you either have both loads hardwired or both using receptacles. However, the instant hot manual only shows plug-in and the disposal only shows hardwired. Unless there are alternatives officially supported by the manufacturer, you should not be switching things around - i.e., don't change the disposal to plug-in or the instant-hot to hardwired. The switch you linked is specifically for use with a receptacle.

My recommendation:

  • If power goes from circuit breaker to disposal to switch, then you already have power in the right place.

  • If power goes from circuit breaker to switch to disposal, you will need to run an additional cable between the switch and the disposal and move things around a bit. But unlike many other situations, this should be pretty easy since it is all near the sink and should be easily accessible. We can outline all the specific details if needed.

  • Below the sink, you will have a box with:

    • Power coming from the circuit breaker
    • Switch loop going up to the switch
    • Disposal connected to the switch loop
    • A single receptacle for the instant hot
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    I really don't see a disposal as a continuous load. – Harper - Reinstate Monica 2 days ago
  • @Harper-ReinstateMonica I agree. Or at least not any normal residential disposal. – manassehkatz-Moving 2 Codidact 2 days ago
  • Re: "the disposal only shows hardwired" -- The Spec sheet shows a plug in the picture and one of the reviews says "this unit is "hard-wire" or outlet-compatible". – philfreo 2 days ago
  • @philfreo This is getting interesting. The installation manual (which is all I looked at earlier) shows drawings and instructions clearly for hardwired. But it has a reference regarding grounding for an optional cord/plug kit - so that indicates it is OK to do so. And the spec page (which I looked at now) does indeed show the plug/cord included. So it seems OK to wire it either way. Personally, I'd still go hardwired for the disposal and plug/cord/receptacle (since it seems required) for the instant hot. – manassehkatz-Moving 2 Codidact 2 days ago
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    If you use an "air switch" that is essentially a switch that goes between a receptacle and the disposal, then it doesn't matter much which way it is wired now. And indeed that part ( STS-OOSN ) looks like it is "real" and reputable. FYI, depending on a number of actors, the receptacle you install may need to include GFCI. – manassehkatz-Moving 2 Codidact 2 days ago

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