Dishwasher + Disposal

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jeff43222

Senior Member
I got a call from a homeowner who had a plumber install a disposal under her kitchen sink, but there's no wiring under there to connect it to. Directly under the kitchen, the basement is completely finished all the way back to the recessed panelboard, which was full. I pulled out the dishwasher and found it hardwired with a length of 14-2 NM; I think it's on an individual branch circuit.

My idea was to reroute the 14-2 to the interior of the cabinet under the kitchen sink, where I'll put it in a box and feed a split-wired receptacle: unswitched hot for the dishwasher and a switch loop for the disposal. I generally like to put the dishwasher and disposal on separate circuits, but in this case that's not really an option. 210.23(A)(2) seems to be the relevant section, and as far as I can tell, having both of these appliances on one 15A circuit would still be legal. My take is that the 50 percent rule only applies when there is lighting or cord-and-plug equipment not fastened in place.
 

rhombus65

Member
IMO you need to check to see what the dishwasher draws. A lot of newer dishwashers require a 20 amp circuit by themselves.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Jeff, you're correct. If this is a dedicated homerun, and feeds solely the dishwasher, then...
  • 210.23 requires that the total load not exceed the rating of the branch circuit. (The circuit breaker says 15 amps.)
  • 210.23(A)(1) places requirements on C&P connected equipment not fastened in place. Both appliances are fastened in place.
  • 210.23(A)(2) requires that if the circuit in question feeds other outlets for general use, or lights, that the fastened appliances not use more than 50% of the circuit's rating. You have no other outlets.
  • 210.19(A)(1) gives requirements for continuous loads. You have none. You can use 100% of the branch circuit's rating.
If you're too concerned, throw the disposal on a threeway.
Common = Power in
Traveller (connected to common in "up" position) = Disposal recep
Traveller (connected to common in "down" position) = Dishwasher recep

If you do that, it doesn't get you anywhere code-wise, I don't believe. But you'll know that only one appliance or the other will run at once. (Just be sure to advise the h/o of your shenanigans. :D )
 

jeff43222

Senior Member
I like the idea of the three-way switch to prevent both appliances from being used at the same time. I've never come across an installation like that, and I suspect it might be a little weird for the average homeowner, as well. Very clever, though. 8)

My main concern here is overload, but I'm stuck with the hand I've been dealt, namely the 14-2 NM wire I'll have to use to make this whole thing work. I didn't see the nameplate on the dishwasher, and I think it's possible that the homeowner is planning on buying a new one. The dishwashers I've been installing lately have all said a 15A circuit is OK, but that generally means a 15A individual circuit.

Realistically, disposals are generally used for only a few seconds at a time, but I could see a situation where someone has a load in the dishwasher and is trying to dispose of an entire evening's worth of food scraps all at once, causing the breaker to kick.
 

stew

Senior Member
dishwasher

dishwasher

I have checked seceral diswashers recently becuase I also had the same question. HAD ONE WHERE AN INSTAHOT WANTED TO BE ON THE D W CIRCUIT. aNYWAY i HAVE CHECKED SEVERAL D/W NAMEPLATES ALL OF WHICH WER IN THE 5.6 TO 6.2 AMP RANGE
 

jeff43222

Senior Member
The plot thickens...

I discovered today that the dishwasher is on the same breaker as the laundry. Inside the panel, the laundry/dishwasher breaker has both hots from a homerun of 12-3 NM under the lug. Fortunately, one of the wires feeds the laundry and one feeds the dishwasher. Unfortunately, the dishwasher is 11A, so the 50% rule precludes moving the wire to another circuit. The panel is a 12/24 GE filled with 24 breakers.

My current plan is to see if I can combine a couple of the less used circuits to free up a space so I can put in a dedicated circuit for the dishwasher/disposal. If anyone has any other bright ideas, I'd be happy to hear them.
 

benaround

Senior Member
Location
Arizona
Maybe a good time to change out the panel/service , sounds like circuits are already doubled up?

The worst they could say is,"O.K. go ahead and do it".
 

jeff43222

Senior Member
We already had the "upgrade" discussion. As I expected, the homeowner wasn't interested. All she wants is her disposal wired up. Upgrading the panel would be expensive, as the whole basement is completely finished, and the drywall guy who fixes textured ceilings isn't terribly cheap.
 
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