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#101331 - 03/07/07 10:35 PM Dishwasher/Disposal  
shortcircuit  Offline
Member
Joined: Jun 2004
Posts: 608
massachusetts
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


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#101332 - 03/07/07 10:46 PM Re: Dishwasher/Disposal  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
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).]


#101333 - 03/08/07 12:30 AM Re: Dishwasher/Disposal  
ShockMe77  Offline
Member
Joined: Jun 2005
Posts: 821
Rahway, New Jersey
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)


#101334 - 03/08/07 02:08 PM Re: Dishwasher/Disposal  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
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!)


#101335 - 03/08/07 10:28 PM Re: Dishwasher/Disposal  
stamcon  Offline
Member
Joined: Mar 2001
Posts: 329
So San Francisco CA
Check for a local amendment. I've seen cities require separate circuits for the DW and disposal.

steve


#101336 - 03/09/07 12:53 AM Re: Dishwasher/Disposal  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
Why would they do that, stamcon?


#101337 - 03/09/07 07:07 AM Re: Dishwasher/Disposal  
shortcircuit  Offline
Member
Joined: Jun 2004
Posts: 608
massachusetts
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


#101338 - 03/09/07 01:19 PM Re: Dishwasher/Disposal  
ShockMe77  Offline
Member
Joined: Jun 2005
Posts: 821
Rahway, New Jersey
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.


#101339 - 03/09/07 02:05 PM Re: Dishwasher/Disposal  
earlydean  Offline
Member
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
dishwashers also have a heating element; they are not a strictly motor load


Earl

#101340 - 03/09/07 05:28 PM Re: Dishwasher/Disposal  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,124
Estero,Fl,usa
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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