i want to know if anybody can help me calculate if i can put a 1/2 HP disposer motor and a dishwasher that draws a nameplate or 9.1 amps on a 20 amp circuit.

Nominal FLA on a 1/2 HP motor is 9.8a (plus 25%) added to 9.1a seems to be too much for a multiple motor load.
If you are cord and plug connected they each do represent less than 50% of circuit ampacity so it might be "hold your nose" legal. I have seen this go both ways but the preferable solution is a multiwire circuit with 2 phases feeding the duplex.

thanks gf i just wondered if possible...
could you elaborate on the 50% since cord connected dishwashers are feasible and do provide disconnecting means for motor.

h2o

It all gets down to how you read
210.23(A)(2) Utilization Equipment Fastened in Place. The total rating of utilization equipment fastened in place, other than luminaires (lighting fixtures), shall not exceed 50 percent of the branch-circuit ampere rating where lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both, are also supplied.

Most inspectors would say all fixed in place equipment must be less than 50% but I have seen this stretched to say any one piece can't exceed 50%, particularly on an intermittant load like a disposal.
Vote me for "all".

One caution here....look at the FLA on the disposal, and not the "horsepower" rating. I have seen a lot of inflated "horsepower ratings" over the years.

"...lighting units (or) cord-and-plug-connected utilization equipment not fastened in place..."

Neither describe either a dishwasher or a disposer, so 210.23(A)(2) doesn't apply.

I routinely place both of these on a 20-amp circuit. A disposer is probably the epitome of an intermittent load.

According to Insinkerator specs, the 1/2HP Badger 5 has an average current draw of 6.9A.
http://www.insinkerator.com/pdf/badger5.PDF

Good subject. I have been told that they make a 3 way switch that can be used in these applications. One position for dishwasher and other for disposal. Now having said that I personally have not seen one. Do they make them?

Any 3-way rated for the load would work.

I am moving this to the NEC section.

I think what should be used is a single pole, double throw switch. on-off-on

They do make an "Air Switch" that has two plugs on it that switches back and forth like a three way. Hit the switch, and the unit takes power supplied to a Hot water dispensor, and turns on the Disposal. Hit the switch again, same in reverse...

However, I wouldn't think of using it, or a 3-way switch like that for a Dish Washer. It would become a nusiance to the home owner to reset the DW cycle everytime the GB was used. And you would have the HO curse your name every time they remembered that you cheaped out and didn't run a circuit for the extra $25 dollars of material and minimal effort. (Not that 'they' would know that, but you would...)

Common practice to just run a 3-wire to the sink for the both as a give-in. Priced that way off the bat. That way you're covered if they up-grade the appliances after rough, or anytime in the future.

Guys:
Just a heads-up; check the nameplate on the DW. 9.1 amps total load; hmm....15 amp OCP
CHECK the nameplate before installing the CB,

GD's vary, 4.9 FLA, 8.25 FLA, etc.

Most guys around here run #12 to DW, 15 amp CB; #14 for disposal....H/R. Most DW are hard wired; disposals are probably a 50/50 mix.

John

Around here we just put the garbage disposal on one of the 2 required appliance circuits and the dishwasher usually gets its own 15 or 20 Amp circuit.It really works well-absolutely no callbacks!

Rhino - No other outlets.... Means no GB/DW, etc. Refers and ignitors for rangetops are an exception and Din rm/ pantry plugs.