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Dishwasher/Disposal #101331 03/07/07 09:35 PM
Joined: Jun 2004
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shortcircuit Offline OP
Member
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

2017 / 2014 NEC & Related Books and Study Guides
Re: Dishwasher/Disposal #101332 03/07/07 09:46 PM
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renosteinke Offline
Cat Servant
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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).]

Re: Dishwasher/Disposal #101333 03/07/07 11:30 PM
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ShockMe77 Offline
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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)

Re: Dishwasher/Disposal #101334 03/08/07 01:08 PM
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SteveFehr Offline
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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!)

Re: Dishwasher/Disposal #101335 03/08/07 09:28 PM
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stamcon Offline
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Check for a local amendment. I've seen cities require separate circuits for the DW and disposal.

steve


Steve
Re: Dishwasher/Disposal #101336 03/08/07 11:53 PM
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SteveFehr Offline
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Why would they do that, stamcon?

Re: Dishwasher/Disposal #101337 03/09/07 06:07 AM
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shortcircuit Offline OP
Member
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

Re: Dishwasher/Disposal #101338 03/09/07 12:19 PM
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ShockMe77 Offline
Member
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.

Re: Dishwasher/Disposal #101339 03/09/07 01:05 PM
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earlydean Offline
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dishwashers also have a heating element; they are not a strictly motor load


Earl
Re: Dishwasher/Disposal #101340 03/09/07 04:28 PM
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gfretwell Offline
Member
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.


Greg Fretwell
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