Can a dishwasher with a nameplate amp rating of 8.7 amps and a disposal with an amp rating of 6.7 amps be connected to the same 20 amp branch circuit?

shortcircuit

And why would that be a problem? I don't see anything near 20 amps on the circuit ,,,, even if you assumed continuous operation!

[This message has been edited by renosteinke (edited 03-07-2007).]

Depends on the manufacturer specifications. I'd check those first. As long as there is no lighting load on the circuit, I say you're good to go!

422.10 (B)
210.23 (A)(2)

Disposals are on for such a short amount of time, they're unliky to ever trip a breaker, irregardless of whatever else is on the circuit- you could already have a 22A overload on that 20A circuit and still never trip it with a disposal.

In your case, I certainly don't see a problem sharing a dishwasher and disposal. In my house, I have the microwave sharing the circuit, too- the duty cycles are so short with so little simultaneity, it's just not a problem. (It wasn't completely intentional or I would have used two circuits... I simply forgot the dishwasher until it was too late to add a new circuit!)

Check for a local amendment. I've seen cities require separate circuits for the DW and disposal.

steve

Why would they do that, stamcon?

Thank you for the replies...

I have always installed a seperate circuit for each appliance, but do not remember why I had been taught to or if it was a code requirement.

I found 430.53(A)which seems to apply?

shortcircuit

430.53 (A) will not help you here because both of your motors are over 1 horsepower. And 430.53 (A)(1) specifically does not allow motors over 6 amps.

1 HP = 746 watts

6.7 amps x 120 volts of alternating current = 804 watts
8.7 amps x 120 volts of alternating current = 1044 watts

Hope that helps you.

dishwashers also have a heating element; they are not a strictly motor load

Shock, don't let that 746w per horsepower thing confuse you. That is a theoretical number. You have to use the nameplate rating or 430.148.
I doubt the dishwasher has more than 1/4hp motor in it and I bet it is smaller. The 8.7a reflects the 1kw heating element and the timer. The disposal is probably 1/2hp, maybe 3/4.
I agree 430.(A)(1) seems to prohibit it but that conflicts with 210.23(A)(2). I also agree with Steve that this will probably never cause a problem and it is not a danger to the 12ga conductors but the AHJ will have to agree with that too.
The more I read the more confused I get. Simply the wording of the first sentence of 430.53(A) is contradictory.
"Several motors, each not exceeding 1 hp in rating, shall be permitted on a nominal 120-volt branch circuit protected at not over 20 amperes", but a 3/4hp motor is 7.6a.

And that all makes sense to me too because when I think Dishwasher and Garbage Disposal I think appliance, not motor. Makes for a good discussion though, doesn't it? It's good to know though that in a pinch (1) 20 AMP circuit is good for both appliances and Code compliant. At least as far as I can see.

For what it's worth,

I have done a few dozen homes with Disposal & GD on a single 20-amp ckt. Never had a call back.

However, I do run a 12/3 MW ckt to a laundry room if the dryer is gas-operated.
I believe that the possibility exists that a load of wet clothes in the dryer and a load of wet clothes on the spin cycle of the washer may trip a single 20-amp ckt if the motors start simultaneously.

Absent any nameplate data, I think it is a safe bet.

8.7 and 6.7 = 15.4 amps. You are also able to round down to 15 amps. the .4 can be rounded down to 15 amps. Check the code book but for whats its worth your good to go.

Coupla things:
If you guys are using 430 for your calculations then it's 1.25 x 8.7 plus 6.7 and your looking at 17.8 as your load. Another thing is we do need to look at the manufacturer's specs and make sure that they don't ask for a dedicated 15 ampere circuit for the appliance. I'm been on both sides of that argument.

George, in the dishwasher, I doubt that the motor is the big load, it will be the heater so you will be doing 1.25% of the disposal, plus the motor load of the WD or the resistive load since they are usually non-coincident. I bet you will be using the resistive load since it is probably larger.
That is a whole lot of calculating, based on an appliance that may not even be ordered when they do the rough and long after the plan review.

This thread is NEC and other codes so let me offer a CEC solution .
Section 28 sizes multiple motor circuits as 1.25 time the largest motor plus the sum of the currents of other motors that would run at the same time or 17.575 amps. For motors this is fine on #12 but the breaker could be undersized if both motors start at the same time. Not a violation here.

The NEC rules are the same on this.


1.25 time the largest motor plus the sum of the currents of other motors that would run at the same time

But as Greg pointed out that Motor in the DW is not 8.7 amps it will be much less than that. Much of that 8.7 amps will be the heater.

Don't think this one needs to go past 210.23 (A)(2)... Over 50% you'll need another circuit.

The problem with 210.23(A)(2) is niether one of these are 10a

Exactly.... Neither is over 50%, or a continuous load. If one were 10.1A, and the other say 3A... It would need a seperate circuit.

But I would normaly make it two anyway - out of force of habit, and general standard.

But gfretwell, even if it were over 50%, dishwashers aren't fastened in place!

Screwed into the cabinet face and connected to the plumbing is not fastened in place?

Mine certainly isn't screwed into anything- hell, it has wheels! It would be a real stretch to consider it "fastened", when the only connetion is a NEMA plug and the plumbing equivilent.

That is a portable appliance like a toaster. You can plug that in a counter top receptacle.

One would think that professionals would agree on this simple question.

It is not like disposals and dishwashers have suddenly appeared.

I think we are just having a discussion about the incongruities in the NEC. We have proved that you can find compelling language for either case, Since these are simply appliances that may not even be present when the decisions are made and the inspection performed, things like "nameplate" may not really mean anything. As a design choice, sharing these may not be a good idea since larger appliances may replace the cheapest thing the builder might choose to install but I am not sure there is really an unambiguous code case to be made. I bet I could get a fight started at the IAEI meeting tomorrow, with different jurisdictions having opposite opinions. The safest answer is always "what does the AHJ say?"

I though the NEC required two separate circuits.
It is a good design to have two circuits, but for the sake of discussion, two circuits are NOT REQUIRED PER NEC??????

Edward

The NEC requires kitchens to have two 'small appliance' circuits for countertop use, and that these receptacles be GFCI protected. These circuits may also serve other locations in the kitchen, pantry, etc.

The NEC is silent as to what's under the counter. Outlets there can be on these required circuits, but they don't have to be. Nor are they requires to be GFCI protected.

A common practice is to serve the dishwasher / disposal from the first receptacle on one of these circuits. In that instance, part of the duplex receptacle will be switch controlled (for the disposal). The circuit then continues to the second receptacle, above the counter, which is the GFCI that protects the rest of the circuit.

Something similar is done with the other required circuit, only the refrigerator is served first, "before" the GFCI.

I believe this meets the requirements of the code; good design is another matter altogether. I've become accustomed to massive kitchens, with more electrical gadgetry than the bridge of the Starship Enterprise. Besides the usual counter, there is an island, a bar, a breakfast nook, a walk-in pantry, a prep / wash area, a wine cooler, a refrigerator that is larger than a Yugo, a trash compactor, a toaster-oven (built in), a microwave big enough to dry your laundry, and enough lights to perform surgery.
Two circuits? Closer to two panels! But, I drift.

Unless you have a booster heater with that dishwasher, there's plenty of room for a disposal on that circuit.

Of course, there IS the Tim-Taylor disposal, with the Briggs & Stratton 2 cycle engine ...