motor question

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Read 430.6(A)(1). This tells you that the 430 table values must be used based on the horsepower rating of the motor, NOT the FLC from the motor label. Without the horsepower rating, you have no idea how to wire this motor. There should be a horsepower rating somewhere. Of course the next sentence tells you that if the motor is only rated in amperes, then you may extrapolate the horsepower from the ampere rating on the label. Thus the never ending circle begins. You must use the horsepower rating to determine the FLA unless it is not given, then you can use the FLA to determine the horsepower. Don't you love the code?
 
haskindm said:
Read 430.6(A)(1). This tells you that the 430 table values must be used based on the horsepower rating of the motor, NOT the FLC from the motor label. Without the horsepower rating, you have no idea how to wire this motor. There should be a horsepower rating somewhere. Of course the next sentence tells you that if the motor is only rated in amperes, then you may extrapolate the horsepower from the ampere rating on the label. Thus the never ending circle begins. You must use the horsepower rating to determine the FLA unless it is not given, then you can use the FLA to determine the horsepower. Don't you love the code?
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ive determined that the motor is 3 horsepower. the 7 horsepower rating is wrong on the side. the 7 horsepower is how much power the motor will create before it burns up. its a little decieving thats why the motor is not marked with the HP.
 
electricalperson said:
ive determined that the motor is 3 horsepower. the 7 horsepower rating is wrong on the side. the 7 horsepower is how much power the motor will create before it burns up. its a little decieving thats why the motor is not marked with the HP.
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I hope they're not using the air compressor for anything intelligent then. Just out of curiosity, what is the RPM rating on the compressor (not motor)? If it doesn't say, what is the RPM of the motor and the two pulley sizes?

Here is a good primer on air compressors and why this HO shouldn't have bought this one: http://www.practicalmachinist.com/vb/showthread.php?t=110655
 
here is the air compressor

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100083906&categoryID=524403

i think the HO got a good deal on it. he didnt have really any reading material thats why i had a little trouble. i searched for an HP rating on the motor when i first looked at it and it didnt say anything so i was confused. i never wired one of these compressors before. I never even wired a compressor like this in a residential garage. Last time i wired a compressor it was in a commercial garage that repairs tractor trailers. the motor was 480volt 3 phase and it was fed by a contactor that was built on the unit. The pressure switch controlled the coil inside the contactor and that is what controlled the motor directly. I installed a motor rated 3 pole industrial switch from hubbel. the entire unit came unwired and i had to wire it from scratch. Not too hard to do but this was my experience with compressors. I went by the rating of the motor on the compressor and thats what i did with the one in this house.
 
electricalperson said:
the motor already has thermal protection builti n so i dont need a contactor for that.
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the two parts to the above statement are independent of each other...you need a contactor if you have a 1pole pressure switch (or other switch) controlling a 2 or 3 pole motor...the fact that the motor already has thermal protection built in, means you don't need thermal overload protection (heaters) to be installed by you...

the overload and the contactor are 2 different parts that do different things..but in the case of a motor, many times they are installed together...
 
emahler said:
the two parts to the above statement are independent of each other...you need a contactor if you have a 1pole pressure switch (or other switch) controlling a 2 or 3 pole motor...the fact that the motor already has thermal protection built in, means you don't need thermal overload protection (heaters) to be installed by you...

the overload and the contactor are 2 different parts that do different things..but in the case of a motor, many times they are installed together...
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i understand that. the pressure switch is 2 pole.
 
On that unit you can come right from the breaker to pressure switch to motor..pressure switch is rated to switch the load and motor has thermal overload built in it..simple straight forward..
 
electricalperson said:
here is the air compressor

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100083906&categoryID=524403

i think the HO got a good deal on it.
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That's not a bad choice for that class of machine, especially if he got a deal on it. The weakest point is probably the motor, maybe the pressure switch, both of which could easily be replaced when they fail. In my area it's possible to get an industrial level machine for $400-500 used, but that takes more work and knowledge than most people are interested in.
 
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