Replies

1. 
   northhouguy | Jan 08, 2009 10:00pm | #1

   Article 430.24 of the National Electrical Code says:

   "Conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity not less than 125 percent of the full-load current rating of the highest rated motor plus the sum of the full-load current ratings of all the other motors in the group, as determined by 430.6(A), plus the ampacity required for the other loads."

   Article 430.6 requires the full load currents to be taken from Table 430.248 for single phase AC motors.  You cannot use the motor nameplate to size the conductors.

   So, in your case, look up the full load current of the largest motor in the table.  Multiply that number by 1.25.  Then add to that value the full load amps, (from the table), of the other motor.  That is the required ampacity of the motor branch circuit conductors.  Then you must match the receptacles and plugs to the breaker rating for the circuit.

   From your nameplate full load amps I'm guessing you have a 2 HP dust collector and a 1-1/2 HP tool.  From the table you would need (12*1.25)+10 = 25 A of branch circuit conductor.  That's a #10 cable protected by a 30 A breaker.  so you would have to use 30A plugs and receptacles throughout.

   Just one other thing, a molded case circuit breaker will only continuously carry 80% of it's rating.  So a 30 A breaker maxes out at 24 A.  You shouldn't have a problem, but it is possible you might get some trips when starting up.

   Good luck and post some pictures of your successes!

   Best Regards,

   Fred    

1. 
   aaronpetersen | Jan 08, 2009 10:11pm | #2

   Fred,

   Thanks for the info! I'll check the table and do the calculations. It's only temporary, but I don't want trouble. Are there any other big problems you see in this type of a setup such as 220v outlets wired in series? Do you think I'm risking the machinery by plugging them into this big of a circuit? By the way, you were close. I have a 2hp DC (12amps), a 2hp bandsaw (10amps), and a 1.75hp hybrid TS (7.5amps). I'm looking to add a 2hp jointer in the near future, so I have to plan for that as well.

   Thanks again for the help!

   Aaron

1. 
   northhouguy | Jan 09, 2009 02:25am | #3

   When you say "series" I assume you mean daisy chained, in other words the receptacles are wired in parallel, one after another.  That's OK, as long as all the motors you plug in have internal thermal protection, the wire to each receptacle is the same size and you can start the 2nd, (or 3rd, or 4th...) motors OK.  But for my permanent installation I chose to run 3 each 20 A circuits.  (That's what I'm doing in my shop as we speak.) That's a personal preference.  I have a lot of space in my sub panel so I know I'm good for 2 HP at each receptacle. 

   I don't see a problem with the 30 A circuit.  Remember, the thermal protection built into the motor protects it from overload.  The 30 A breaker is short circuit protection.  If you get a short in the motor you want it to trip quickly.  The code actually allows you to oversize the breaker, (and thus the wire), on a motor circuit if you have starting troubles. 

   Fred