Dishwasher and Disposal wiring.

[iwire]

argghh i cannot cite a code reference
which means i am probably wrong

That is often the case.

Some people think I 'know' the NEC, not true, I know how to look things up.

I pretty much check the NEC each time I post to keep from putting my foot in my mouth. (Still Happens :roll: )

i have been taught that we cannot load a breaker to more than 80 percent

In some cases that is true, it is not always true.

if you load a 20 amp breaker to 18 or 19 amps, it will get Hot, and trip eventually.

A 20 amp breaker should hold a 19.9 amp load for at least 3 hours.

However the typical breakers we use are not high tech, extremely accurate devices. They are fairly crude devices that will trip near their rating.

If you look at breaker trip curves (available from the manufacturer) you will find that a typical 20 amp breaker may trip early or not at all.

A typical correctly functioning 20 amp breaker may 'hold' a 25 amp load forever.

At 30 amps it may take minutes to trip.

 

[1793]

I come up with 18.7 which would still make it legal. NEC 430.24

Could you elaborate on your answer ?

I think it comes from the following:

9.6 * 1.25 (430.24) + 6.7=18.7

Why the 125%? Does a dishwasher run continuously for more than 3 hours?

Read 430.24 First statements something like "for several motors you take the largest load and add 125% then add the other motor loads."
This does seem to be talking about conductors

I now think I'm wrong about OC so now I am confused.

I still think both Disposer and Dishwasher could be on one 20 circuit.

 

[Stu Goforth]

LarryFine. I too have been in this industry for over 30 yrs and have almost always used a shared 20A ckt. New inspectors wet behind the ears don't due justice to our industry.
Again thanks to all for the comments it had given me some things to consider from now on.


Stu

 

[dnem]

Read 430.24 First statements something like "for several motors you take the largest load and add 125% then add the other motor loads."
This does seem to be talking about conductors

I now think I'm wrong about OC so now I am confused.

I still think both Disposer and Dishwasher could be on one 20 circuit.

"This does seem to be talking about conductors

I now think I'm wrong about OC so now I am confused."

This is a good point and one that should be addressed when referencing 430 for an ampacity question. 240.4 says that "Conductors" ... "shall be protected against overcurrent in accordance with their ampacities" ... "unless otherwise permitted or required in 240.4(A) thru (G)." And 240.4(G) says that Table 240.4(G) exempts motors.

When talking about motors, a particular code restriction might apply to the motor, to the wire, or to both.

David

 

[dnem]

210.23(A)(2) would only apply if the dishwasher wasn't screwed into the countertop. Has anybody ever seen a dishwasher that wasn't permanently attached with screws ?

If the manufacturers instructions say that the dishwasher must be on its own dedicated circuit, there's no way around it then. If you're dealing with a completed job when the dishwasher comes and you find out about the restriction too late to separate the dishwasher from the disposal, then use the 3way idea that somebody else posted.

David

 

[Jim W in Tampa]

210.23(A)(2) would only apply if the dishwasher wasn't screwed into the countertop. Has anybody ever seen a dishwasher that wasn't permanently attached with screws ?

If the manufacturers instructions say that the dishwasher must be on its own dedicated circuit, there's no way around it then. If you're dealing with a completed job when the dishwasher comes and you find out about the restriction too late to separate the dishwasher from the disposal, then use the 3way idea that somebody else posted.

David

Somehow that idea of a 3 way just would not fly with most on a new house.If it was mine you would be running a hr and paying for drywall and painter.How much did you save now.

 

[roger]

Somehow that idea of a 3 way just would not fly with most on a new house.If it was mine you would be running a hr and paying for drywall and painter.How much did you save now.

Jim, please elaborate on your statement. Surely your joking or just not understanding the installation as described.

There will be a switch for the disposal in any event.


Roger

 

[Jim W in Tampa]

Somehow that idea of a 3 way just would not fly with most on a new house.If it was mine you would be running a hr and paying for drywall and painter.How much did you save now.

Jim, please elaborate on your statement. Surely your joking or just not understanding the installation as described.

There will be a switch for the disposal in any event.


Roger

So what you have in mind is shutting off the dw to run the pig.They do things like this on RV'S but never seen it in a house

 

[George Stolz]

...then use the 3way idea that somebody else posted.

Can you cite a code reference allowing a circuit to be loaded in excess of it's rating by use of a threeway switch? :?:

 

[iwire]

...then use the 3way idea that somebody else posted.

Can you cite a code reference allowing a circuit to be loaded in excess of it's rating by use of a threeway switch? :?:

We don't need one. 8)

210.19 Conductors ? Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served.......

210.20 Overcurrent Protection.
Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).
(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

The installation of the SPDT switch prohibits the load from exceeding the capacity of the circuit.

If you have an HVAC unit with both AC and heat is the circuit supplying it large enough to run both at once?

 

[dlhoule]

In terms of SPDT for DW/Disposal, I am somewhat neutral. I consider it legal and as far as most homes: most people rinse off the dishes and run the disposal before running the DW. Very seldom is there any desire to run both at the same time.

 

[romeo]

A SPDT switch may be a workable sulotion. But in my oppinion not a practical one. Pepole buying homes at todays prices should be able to run a dishwasher washer and disposal at the same time if they chose to do so.

 

[dnem]

...then use the 3way idea that somebody else posted.

Can you cite a code reference allowing a circuit to be loaded in excess of it's rating by use of a threeway switch? :?:

We don't need one. 8)

210.19 Conductors ? Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served.......

The installation of the SPDT switch prohibits the load from exceeding the capacity of the circuit.

If you have an HVAC unit with both AC and heat is the circuit supplying it large enough to run both at once?

210.19 "max load to be served" is a good reference.
422.12x2 is a good reference example for AC and furnace that doesn't run at the same time so the max load served is the larger of the two and not both loads combined.
The thermostat serves the same function as a 3way by not allowing both units to be energized at the same time.

The 3way would be OK in a pinch, on the final. But I don't think the 3way is a good solution on the rough. If the dishwasher has a mechanical dial, then if someone uses the disposal while the dishwasher is running, the dishwasher shuts off for a moment and then just picks right back up where it left off. But if the dishwasher has electronic controls, then if someone uses the disposal while the dishwasher is running, the dishwasher might have to be reprogrammed. That would be a bad set up and cause the person to bypass the 3way and connect the dishwasher directly to the unswitched power in the switch box.

David

 

[George Stolz]

...then use the 3way idea that somebody else posted.

Can you cite a code reference allowing a circuit to be loaded in excess of it's rating by use of a threeway switch? :?:

We don't need one. 8)

You cited the same section I would to defend my position.

210.20(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

What loads are present on the circuit? What do you write on the panel schedule?

 

[dnem]

A SPDT switch may be a workable sulotion. But in my oppinion not a practical one. Pepole buying homes at todays prices should be able to run a dishwasher washer and disposal at the same time if they chose to do so.

I need you guys to explain something to me.

Both you and Bob have used the term "SPDT" to describe a 3way. I first heard this used for a 3way last week at the annual Ohio IAEI meeting. I'm trying to figure out how a 3way can be considered single pole double throw.

This is what's throwing me off.
Two single poles in the same yoke and case controlled by a single toggle switch is called a double pole single throw. There's one single toggle that has only 2 possible positions, on and off.

The 3way has one single toggle that has only 2 possible positions but I'm hearing it called double throw. I don't understand how these terms are applied. What piece of information am I missing ?

David

 

[dnem]

What loads are present on the circuit? What do you write on the panel schedule?

Handle the panel schedule for the dishwasher/disposal the same way you would mark the AC/Furnace breaker.

 

[infinity]

A 3-way switch is in fact an SPDT switch. A single pole double throw switch has one common terminal, the pole (or black screw on the 3-way). The "throw" is the number of positions it has that will connect to the common pole. So a SPDT has one pole or common and two positions that the common can connect to.

 

[dnem]

The "throw" is the number of positions it has that will connect to the common pole.

That makes sense. I'd never heard that explanation before.
Thanks

 

[dlhoule]

David

But if the dishwasher has electronic controls, then if someone uses the disposal while the dishwasher is running, the dishwasher might have to be reprogrammed. That would be a bad set up and cause the person to bypass the 3way and connect the dishwasher directly to the unswitched power in the switch box

.

I can't say for all dw, but on some of them flipping that switch would not be any different than opening door of dw to load another item.

Given differences in cost I prefer to run separate circuits, just to be on safe side. I do not think it will make much (if any) difference in the vast majority of cases.

 

[allenwayne]

If a 3 way is used wouldn`t there have to be either cord connects or breaker lock outs since a 3 way is non indicating :wink: