DIY wiring question

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blood_donor
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Location: Metro Detroit, MI

DIY wiring question

Post by blood_donor » Sat Aug 23, 2008 9:41 pm

Hi,

In an effort to save some money, I am installing my own dishwasher, after the 25 year old previous one croaked.

The old machine was wired directly to a 15 amp power line which also fed the garbage disposal, but it was a sloppy splice job that is obviously not up to code (was not done in a junction box). I'll be repairing that wiring mess.

I'd like to plug the new dishwasher into a wall plug which is on a 20A breaker, which also runs my refrigerator.

Do you guys know if this will work, or will the load from the fridge be so high that if I try to run the dishwasher it will pop the 20A breaker?

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NAVigator
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Post by NAVigator » Sat Aug 23, 2008 10:00 pm

According to this book by Ray Mullin, I would not wire the dishwasher into the same circuit that supplies the refrigerator. See page 309.

House Wiring With the National Electrical Code

The total current of the dishwasher is substantial as is the refrigerator.

The national code does not appear to address this directly, but the local code probably does.

Jerry
"I was born with nothing and I have most of it left."

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ualdriver
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Re: DIY wiring question

Post by ualdriver » Sat Aug 23, 2008 10:11 pm

blood_donor wrote:Hi,

In an effort to save some money, I am installing my own dishwasher, after the 25 year old previous one croaked.

The old machine was wired directly to a 15 amp power line which also fed the garbage disposal, but it was a sloppy splice job that is obviously not up to code (was not done in a junction box). I'll be repairing that wiring mess.

I'd like to plug the new dishwasher into a wall plug which is on a 20A breaker, which also runs my refrigerator.

Do you guys know if this will work, or will the load from the fridge be so high that if I try to run the dishwasher it will pop the 20A breaker?
Even if it meets code , I wouldn't wire it like that anyway. You wouldn't want a dishwasher electrical fault that trips the shared breaker to kill electricity to your refrigerator and spoil your food!

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blood_donor
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Location: Metro Detroit, MI

Post by blood_donor » Sat Aug 23, 2008 10:20 pm

Wow, thanks, that is a great resource!

According to the book, a typical dishwasher may draw about 8.3A, or 15.5A if hypothetically the motor and heating coil were running at the same time.

The sticker on my dishwasher says "8.6 Total Amps".

It looks like my fridge is rated at 6.5A for "Full Load Demand" according to the sticker.

So, if my dishwasher uses 8.6 max and my fridge uses 6.5, I should be OK with them sharing a 20A circuit, right?

Am I missing something?
Last edited by blood_donor on Sat Aug 23, 2008 10:31 pm, edited 1 time in total.

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NAVigator
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Post by NAVigator » Sat Aug 23, 2008 10:30 pm

Given your maximum current demand, it is within the limits of the 20 A circuit. It appears to be okay to do this. I would check on local codes. I have found this to be very difficult to do. Good luck!

BTW, in one city where I lived, the dishwasher was required to be on a switched circuit. So, there was a toggle switch (aka light switch) that controlled the power to the dishwasher. Local codes are interesting.

Jerry
"I was born with nothing and I have most of it left."

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blood_donor
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Re: DIY wiring question

Post by blood_donor » Sat Aug 23, 2008 10:32 pm

There is some wisdom, here.
ualdriver wrote: Even if it meets code , I wouldn't wire it like that anyway. You wouldn't want a dishwasher electrical fault that trips the shared breaker to kill electricity to your refrigerator and spoil your food!

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DiscoBunny1979
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Re: DIY wiring question

Post by DiscoBunny1979 » Sun Aug 24, 2008 11:02 am

blood_donor wrote:Hi,

In an effort to save some money, I am installing my own dishwasher, after the 25 year old previous one croaked.

The old machine was wired directly to a 15 amp power line which also fed the garbage disposal, but it was a sloppy splice job that is obviously not up to code (was not done in a junction box). I'll be repairing that wiring mess.

I'd like to plug the new dishwasher into a wall plug which is on a 20A breaker, which also runs my refrigerator.

Do you guys know if this will work, or will the load from the fridge be so high that if I try to run the dishwasher it will pop the 20A breaker?
--------------
I recommend putting the dishwasher and fridge on seperate circuits. It's not just about the power required to run both on the same circuit, but for safety reasons. Sometimes new appliances require consistency with local codes so that warranties will be valid. Additionally, some upgraded dishwashers, like Jenn Air Stainless, sometimes require direct wiring and not plugged in. Therefore, it's in the best interest to run a seperate circuit especially for the future repairs and the possibity of future replacements - turning off the circuit doesn't also turn off the fridge.

When replacing a Dishwasher, I would check with local code department to determine what their requirements are. Considering you state that you are replacing a 25 year old one - codes could be much different today. This means that when and if you want to sell your home, not installing the dishwasher correctly could mean the difference between selling or not selling your house. Some people do check to see what was done to "code" . . . FHA, especially loans to veterans, require that houses pass a thorough inspection that everything works according to certain standards.

Finally, the main safety factor is fire danger. About 33% of electrical house fires are from faulty wiring. One of the key factors is overloading circuits. If you are going to still run the fridge and dishwasher from the same circuit, I would hire and electrician to determine whether the circuit can actually handle the appliances, rather than assuming it can because the numbers look good on paper.

boffalora
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Post by boffalora » Sun Aug 24, 2008 11:34 am

Let's get back to what you have today. It's salvageable and you really should reuse it. That sloppily-terminated 15A circuit is sufficient to handle both the dishwasher and the disposer.

Turn off the breaker that serves that circuit (natch), crawl under the sink and cut the wiring loose, leaving enough cable protruding from the wall to reterminate it in a surface-mounted steel box with a standard 115V double duplex "quad" outlet. Notice that one of the duplex outlets will be directly served by your feeder cable; this will serve the dishwasher. The other duplex outlet will be wired in series with the wiring from the switch on the backsplash controlling it. This one will serve the disposer. Mark the two outlets clearly on their front plate with permanent marker, DW and DISP to keep them straight.

(You can also split one duplex outlet to accomplish the same thing; describing it in writing to someone unfamiliar with wiring might be difficult. Please let us know your familiarity level with electrical work.)

Reterminate the cable coming from the disposer in a heavy-duty grounded orange or yellow 115V plug (or alternately, change the wiring from the disposer to a premanufactured cord with a molded grounded plug...the same type that would come on a microwave oven). Plug the disposer in to the DISP outlet.

When you install your new dishwasher, use a length of 14/3G burial cable from the dishwasher's own electrical box to another heavy-duty orange or yellow grounded plug, which you'll plug into the DW receptacle.

Now you have an up-to-code installation that will make an electrical inspector proud. :-)

boffalora
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Post by boffalora » Sun Aug 24, 2008 5:42 pm

Whoops...you won't need that 14/3G cable...just 14/2G (that means 14 gauge, 2 conductor plus ground wire). I suggest the burial-type cable (this will be with heavy gray molded insulation) just in case a leak develops in the dishwasher or under the sink.

Please fire back any questions.

dryfly
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Post by dryfly » Sun Aug 24, 2008 9:38 pm

boffalora wrote:Let's get back to what you have today. It's salvageable and you really should reuse it. That sloppily-terminated 15A circuit is sufficient to handle both the dishwasher and the disposer.

Turn off the breaker that serves that circuit (natch), crawl under the sink and cut the wiring loose, leaving enough cable protruding from the wall to reterminate it in a surface-mounted steel box with a standard 115V double duplex "quad" outlet. Notice that one of the duplex outlets will be directly served by your feeder cable; this will serve the dishwasher. The other duplex outlet will be wired in series with the wiring from the switch on the backsplash controlling it. This one will serve the disposer. Mark the two outlets clearly on their front plate with permanent marker, DW and DISP to keep them straight.

(You can also split one duplex outlet to accomplish the same thing; describing it in writing to someone unfamiliar with wiring might be difficult. Please let us know your familiarity level with electrical work.)

Reterminate the cable coming from the disposer in a heavy-duty grounded orange or yellow 115V plug (or alternately, change the wiring from the disposer to a premanufactured cord with a molded grounded plug...the same type that would come on a microwave oven). Plug the disposer in to the DISP outlet.

When you install your new dishwasher, use a length of 14/3G burial cable from the dishwasher's own electrical box to another heavy-duty orange or yellow grounded plug, which you'll plug into the DW receptacle.

Now you have an up-to-code installation that will make an electrical inspector proud. :-)
I completely agree with the above suggestion. I have a house built 9 years ago and the dw and disp are wired this way but on one duplex outlet.

I do a lot of my own electrical work but don't pay attention to code as we live out of the city limits. I do pay attention to good electrical common sense and practices!

Also, I would have no issue in connecting to the circuit with the fridge. If the breaker trips you will realize the fridge is not running long before food spoils.

good luck and safe wiring!

boffalora
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Post by boffalora » Mon Aug 25, 2008 12:12 pm

bd, if you'd like me to draw a wiring diagram for this job, including the technique for splitting one duplex outlet to serve both DW and DISP (this will enable you to use a less-expensive single-outlet steel box), give me an email address and I'll send you the diagram as a PDF attachment.

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Vig Oren
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Get it done per code!

Post by Vig Oren » Mon Aug 25, 2008 12:35 pm

If you are NOT a certified electrician I would not fool around with this wiring b/c if someone gets electrocuted and the wiring is NOT per LOCAL code, you could be blamed (also after you sell the house). Should not cost more than $120 per point.
Last edited by Vig Oren on Thu Aug 28, 2008 9:09 am, edited 1 time in total.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | "One of the greatest piece of economic wisdom is to know what you do not know"{John Galbraith}

boffalora
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Post by boffalora » Mon Aug 25, 2008 2:27 pm

Well, Vig, sounds like you need to go over and give him a bid.

boffalora
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Post by boffalora » Mon Aug 25, 2008 7:18 pm

Let's try this again.

Didn't mean to jump your case, Vig.

My immediate assumption was that you were a militant union electrician who couldn't stand the thought of a DIY job done, even within the National Electrical Code.

Or you might be a litigation attorney who has seen his share of hard-fought liability cases and either welcomes or dreads hearing about another.

But both of those assumptions are most likely wrong. Getting down to the meat of your post, I agree with you...someone who is not comfortable with doing electrical work should not do it...period. He should hire a professional for the peace of mind.

However, it appears that bd is trying to get himself educated in this area and is seeking every bit of input he can get. Once he's accumulated all he needs to make a proper decision, I trust he'll make it.

bd, my offer of additional input stands.

northend
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Post by northend » Wed Aug 27, 2008 11:43 pm

Page 113 of book posted earlier states that the dishwasher and garbage disposal must be on a separate 20 amp circuit.

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verbose
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Post by verbose » Thu Aug 28, 2008 10:19 am

I once had a dishwasher on the same 15A circuit as the microwave. It was an old house that originally had neither appliance, and only those two appliances were on that circuit. We had to be very careful not to run the microwave while the dishwasher was running, because it guaranteed a breaker trip.

And, I was kicking myself because it was our addition of a dishwasher that created this problem!! Not thinking I suppose... now I know better.

boffalora
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Post by boffalora » Thu Aug 28, 2008 11:45 am

Right you are, verbose. A microwave oven is another story entirely. It can pull too much current to be on the same circuit as another major appliance.

A disposer, on the other hand, only is in danger of pulling too much current if it is jammed and the motor begins to overheat from not being able to spin freely. This is why disposers have their own overcurrent protection that will trip under such circumstances before the breaker does. See the RESET button on the bottom of the disposer case.

I'm surprised that the present code calls for a disposer/dishwasher circuit to be 20A rather than 15A. I wonder if they've done this in consideration of those new double-drawer dishwashers.

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