MCA

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Information from label on Grain Drying Equipment:
240V 3PH 60 Hz
218 Full load amps
70.2 largest motor amps. I am guessing this is nameplate data of the motor. There are two of these motors that start one after the other timed to allow the first to be at full speed before the next starts.

70.2 is not in table 430.250. Are they 25 hp @ 68A or a 30 hp @ 80A? Each * 1.25 = 87.5, 85 and 100 respectively.

I need to figure MCA of my feeder.

218-70.2=147.8 (all other loads which no doubt include motors that may also be using nameplate data instead of the table.)

Do I search each motor horsepower and recalculate load or use one of the calculated values above? Using the 30hp values would change my feeder size from 250kcmil cu to 300s. Parrallel is not an option due to lugs in dryer.
 
I'd use the nameplate value (70.2A). I know many think they have to use the nominal HP values given in the "table", but 430.6 says, "Where a motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be that corresponding to the value given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250, interpolated if necessary." Welll exactly what deems a necessity??? And once you interpolate, what do you do with the interpolated HP value???

Additionally, I don't see where it changes feeder size. Using the full load amps of the nameplate (218) and allowing 125% for the largest motor results in a difference range of 3 amps: 68, 70.2, 80 each entered into i?1.25+218-i yields 235, 235.55, 238 respectively.
 
If motor is in air stream you get non standard ratings - they figure they can load it harder as it will get cooling it needs.

It been so dry lately they are not going to need grain dryer this season anyway.
 
kwired said:
If motor is in air stream you get non standard ratings - they figure they can load it harder as it will get cooling it needs.

It been so dry lately they are not going to need grain dryer this season anyway.
Click to expand...

I installed the two dryers we are replacing with one, about 20 years ago. They were used then. I was pretty proud of the system then. It worked & would have passed an inspection. Now some of it is questionable by todays requirements. Industrial control panel requirements will just about kill any farm control systems if they ever start inspection and enforcement of that section.

Dry is right. Two years or so ago I had about 40' of water above my residential pump. We had to lower it another 40' this week to keep it from pumping air.

Iirrigation is just barely keeping up with the needs.
 
Maybe this is another of one of those things where I find out I've been "doing it wrong" for 50 years :D,
but if the nameplate shows MCA of 218 amps, that's the number I would use in sizing my supply circuit without worrying about how that was derived.
 
augie47 said:
Maybe this is another of one of those things where I find out I've been "doing it wrong" for 50 years :D,
but if the nameplate shows MCA of 218 amps, that's the number I would use in sizing my supply circuit without worrying about how that was derived.
Click to expand...

If it had said MCA, I would agree with you. It just gave the FLA of the equipment that has multiple motors.
 
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