Updated: May 5
One of the most common questions we get from electrical contractors is about being able to put both a Dishwasher and In-Sink Waster Disposer on the same branch circuit in a dwelling. Now, I will answer this but if you are the VIDEO WATCHING type person and would like a truly amazing video explaining this then visit Ryan Jackson's Youtube Channel ( https://www.youtube.com/watch?v=F86My4h2zzA&t=743s ).
While I have explained this in the past on numerous occasions the video by Ryan sparked an interest in the topic by many who email me shortly after Ryan's video aired asking me to comment. I did in fact comment on Ryan's post and as always it was an excellent interpretation and what I and many others have come to expect of Ryan.
So, the question is can you install a Dishwasher and In-Sink Waster Disposer on the same branch circuit? Yes and No, Possibly. That seems like the typical answer from a code geek right? Let me explain a bit and you will understand.
The National Electrical Code® (NEC®) permits us (paraphrasing of course) to load a branch circuit in accordance with the circuit's ampacity rating. If the circuit has continuous loads then the installer takes the actual load at 125% and sizes accordingly but if the load is not considered continuous, that is defined as at its maximum ampere rating continuously for 3 hours or more or as dictated by the specific language of the NEC then you take it at 100% of the actual load. These rules can be found in 210.19 for conductors and 210.20 for overcurrent devices, such as circuit breakers and fuses.
Now, of course, if the instructions, which are part of the listing for the appliance, call for an individual branch circuit to supply power to the specific appliance then that would be all that could be on that Individual Branch Circuit, as defined in Article 100.
So, let's assume an In-Sink Waste Disposer at 8 Amps and a Dishwasher at 9 Amps and we would like to run a single 20 AMP-rated branch circuit and these are the only appliances on this branch circuit. The total amps of both would be 8 Amps + 9 Amps = 17 Amps.
Since these are not considered "continuous loads" as defined in Article 100, they would be perfectly compliant on a 20 Amp branch Circuit. Now, I am obviously playing with numbers here but you get the concept that is being applied as it says in 210.23, "In no case shall the load exceed the branch-circuit ampere rating" and it clearly doesn't as the rating is 20 Amps.
Now, here is where it gets complicated for many folks.
The application of 210.23(A)(1) and (A)(2) only comes into play if the 15 or 20-amp branch circuit, the dishwasher, and in-sink waste disposer in our example, also supply lighting units or other utilization equipment, or both. Remember, 210.23(A)(1) and (A)(2) are about the equipment and what can be connected to the branch circuit rather than the branch circuit itself.
In summary, if you are installing a branch circuit to a Dishwasher and In-Sink Waster Disposer (thinking of them as simply two loads) you are 100% compliant as long as the combined nameplate ampere ratings do not exceed the rating of the branch circuit.
Hopefully, you enjoyed this short article and again I encourage you to watch Ryan's video at the opening of this article. Ryan is an amazing resource to our industry and his delivery method is stellar.
Paul Abernathy, CMECP® | CEO & President
Electrical Code Academy, Inc. | www.FastTraxSystem.com 3913 Edward Drive., McKinney, TX 75071 Office: 214-945-0653
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