How To Wire Dishwasher and Garbage Disposal on Same Circuit

At this home there is a 20 amp breaker in the electrical panel that is penc
il labeled as for the dishwasher and garbage disposal. At the junction box
on the kitchen wall near the sink we see the 12 gauge wire feeds from the p
anel. Three 14 gauge wires, hot-black/neutral-white/ground-green, are route
d from this box to another junction box underneath the sink through conduit
. A whip from the dishwasher is hardwired to the wires under the sink.
We want to add a GE half horsepower garbage disposal that is suppose to dra
w only 4.5 amps. Can we just pull another hot 14 gauge wire for the garbage
disposal and use the existing white neurtal already there for the dishwash
er? Does it matter whether 14 gauge is used rather than 12 gauge wires for
either device?
Reply to
Edge
On Sun, 8 Dec 2013 09:42:47 -0800 (PST), Edge wrote:
All the wires should usually be #12 BUT if you are serving a pure motor load like the disposal, you could use #14. (125% of FLA) Not so with the dish washer since it is not a pure motor load. Whether they can share the circuit would depend on the nameplate rating of the dishwasher. Take 125% of the largest load and 100% of the other one. It has to be 20 or less.
Reply to
gfretwell
The other way around, Without the air gap, waste water from the drain siphons back into the dish washer
Reply to
gfretwell
I'd consult the building inspector who is gonna approve it on that. He may frown on using less than #12 on a 20A breaker.
(125% of FLA) Not so
Reply to
mike
Mixing 12ga and 14ga on one branch? That sounds like a real no-no, even if you used a 15A breaker.
Reply to
krw
Not illegal or even unusual. If you had a post light and a gate opener at the end of a long driveway you might want 12ga on your 15a circuit going down there, just for the voltage drop and between the opener and the light, 14 would be fine.
Is it worth doing to save a nickel on this 3' of 14. Not really but it might not be illegal.
Bear in mind there are a few jurisdictions in the US that won't let you use 14 for anything but that is a local amendment, made by idiots.
Reply to
gfretwell
I was thinking that many dishwashers have a heating element that could bring a high resistive load into consideration. ^_^
TDD
Reply to
The Daring Dufas
The city engineering department around here wants the breaker sized for the wire. It's possible that in the warmer temperatures we experience here in Alabamastan, the wire and breakers must be derated to deal with it to prevent nuisance tripping. I have checked the temperatures of many electrical panels with my infrared thermometer and they get quite hot at times under normal loads. Of course I'm looking for that hottest breaker which could indicate a bad connection. ^_^
TDD
Reply to
The Daring Dufas
I believe I've seen them on the same circuit before but I haven't done house wiring as an electrician in years and the dishwasher here is on a separate circuit. I'd have to go look at the outdoor breaker panel to determine what size breaker and wire it is because I didn't install it. Besides, I have a bit of trouble walking and it's raining hogs and frogs outside right now. ^_^
TDD
Reply to
The Daring Dufas
wrote:
I don't see a problem using 15 amp breaker. I use 20 amp breaker feeding 10 ga. To 12 ga. Long run to garage. There can be a long term problem if things are not labeled.
Greg
Reply to
gregz
On Mon, 9 Dec 2013 02:41:30 +0000 (UTC), gregz wrote:
The issue is the next guy who comes along, seeing the 12ga wire, inserts a 20A breaker. ...but I'll defer to those with a citation in their hot little hands.
Reply to
krw
I believe gfretwell is/was an electrical inspector and he is going by the NEC. The problem comes in when you have a city engineering department that has its own interpretation of the National Electrical Code like where I live. Anyone getting an inspection must do as the inspector demands even if you believe him/her/it to be wrong. You can sometimes pull out the code book and win an argument but unless it's an absolutely insane demand, it's best not to argue with the inspector. ^_^
TDD
Reply to
The Daring Dufas
"The NEC does not address what an unqualified person might do". I got that straight from the NFPA on a proposed change about something similar.
I suppose I could blow everyone's mind by saying it is legal to use a 40a breaker on 14 ga wire if you are serving a 1HP single phase 120v motor with internal overload protection.
It is a common question in the inspector test.
FLA is 16a (Table 430.248) 125% of that is 20a (430.22) Table 316.16 says a 14 ga copper wire is OK for 20a in the 60c column.
The over current device can be up to 250% of FLA. 16 x 2.5 = 40a (table 430.52) if the motor has overload protection.
Reply to
gfretwell
How does the overload protection protect the wiring?
Reply to
krw
The overload protection in this case is inside the motor itself. It's a common misconception among home inspectors too. Some of them see a 50A breaker going to an AC compressor and assume that it has to use the same size conductor that you would use for a 50A oven. They see a smaller conductor and flag it, though it's 100% code compliant to use a smaller conductor, within the rating of the AC unit specs.
Reply to
trader4
You know, you're remarkably arrogant for someone who knows so little. You didn't even know how motor loads are sized. Gfre, who is/was an electrical inspector told you that you were wrong.
And what I just told you is correct. The overload protection is in the motor. That protects the motor and the *wiring* from overload, because the motor is the load. Capiche? Or would you like to dig your hole deeper?
Reply to
trader4

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