malachi constant
Senior Member
- Location
- Minneapolis
At least I think it's easy...
5HP 208V 3P motor - typical pump, exhaust fan, etc type motor that you'd find in a commercial building. That's about all the information the mechanical engineer and shop drawings will tell you. What's the conductor size?
430.22(A) states that for single motor continuous duty applications the conductor shall have an ampacity of not less than 125% the motor's FLC. This refers you to 430.6(A)(1) which refers you to Table 430.250, which states FLC is 16.7A. 16.7A x 1.25 = 20.875A. From Table 310.16 and 240.4(D) #12 is only good for 20A, so #10 is the correct size.
Right???
I ask because our motor schedule is an automated Excel spreadsheet that an engineer wrote who is no longer around, and it spits out #12s for some motors with a FLAx1.25 that is greater than 20A - which based on my understanding of the code is wrong. And another "cheat sheet" I have, this one being used for the last 20 years or so at a good-sized engineering firm, has on their motor tables a 5HP motor fed with a #12. I think #10 is correct for a 5HP motor but before I redo the spreadsheet/tables I figured I'd better do a little more research.
Thanks!
5HP 208V 3P motor - typical pump, exhaust fan, etc type motor that you'd find in a commercial building. That's about all the information the mechanical engineer and shop drawings will tell you. What's the conductor size?
430.22(A) states that for single motor continuous duty applications the conductor shall have an ampacity of not less than 125% the motor's FLC. This refers you to 430.6(A)(1) which refers you to Table 430.250, which states FLC is 16.7A. 16.7A x 1.25 = 20.875A. From Table 310.16 and 240.4(D) #12 is only good for 20A, so #10 is the correct size.
Right???
I ask because our motor schedule is an automated Excel spreadsheet that an engineer wrote who is no longer around, and it spits out #12s for some motors with a FLAx1.25 that is greater than 20A - which based on my understanding of the code is wrong. And another "cheat sheet" I have, this one being used for the last 20 years or so at a good-sized engineering firm, has on their motor tables a 5HP motor fed with a #12. I think #10 is correct for a 5HP motor but before I redo the spreadsheet/tables I figured I'd better do a little more research.
Thanks!