How To Wire Dishwasher and Garbage Disposal on Same Circuit

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On Tuesday, December 10, 2013 4:35:29 PM UTC-5, snipped-for-privacy@attt.bizz wrote:

You asked:
"How does the overload protection protect the wiring?"
I replied with:
"The overload protection in this case is inside the motor itself."
And when you didn't understand that, I told stated:
"The overload protection is in the motor. That protects the motor and the *wiring* from overload, because the motor is the load."
Since you're having trouble, I'll try to explain it at your level. If the load, ie the motor seizes up, starts to burn up, etc and it results in an overload, the overload protection in the motor cuts it off. There is no other load, you can't plug in more motors, more lights to "overload" the wiring. Therefore that protection in the motor protects the motor and the wires serving it from overload. Words have meaning you know...
If that is beyond your comprehension level, that's OK. The folks that write the NEC understand it, cover it, set the rules for conductor sizing for it, as GFRE also tried to explain to you.
So, your incredulity once again shows that you don't know what you're talking about when it comes to even practical application of electricity.
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On Tue, 10 Dec 2013 15:37:52 -0800 (PST), " snipped-for-privacy@optonline.net"

That is correct. There are 2 issues here. Overload protection is all about the current the motor draws. That is internal in the motor or in the motor starter if you have one. The branch circuit over current protection (panel breaker) is there to handle faults in the wiring and that can be at a significantly higher rating than you have in a general use circuit where there is no supplemental overload protection.
The article people seem to know the best is 240.4(D) that has the good old 14ga a and 12ga - 20a is actually a modification to the general rules for "small conductors". It used to just be a foot note to table 310.16, the basic ampacity tables. This was added because these small conductors are most likely to be on circuits with receptacles where the end user gets to select the load. You only have to look at holiday decorations to see that in action. People keep plugging in lights until the breaker trips and they unplug a string or two.
240.4(D) enforces that good old 80% safety factor we want by limiting the breaker to 80% of what the wire is actually good for. 240.4(D) does have the disclaimer "unless otherwise permitted in the code" and some of those permissions are in the dedicated motor circuits, HVAC condensers and welders.
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The other way around, Without the air gap, waste water from the drain siphons back into the dish washer
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wrote:

My possibly not-to-code answer. Unless you plan to run the disposal for long periods of time, like 10 or more minutes at a time, I personally would not worry about it and just add the circuit. The only time the load would be particularly high would be if you happened to run the dishwasher and disposal at the same time and as I said, unless you are planning on marathon disposal sessions you just won't be loading the circuit long enough to be an issue.
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