fredspence1
Member
I'm an old Tom Henry disciple. One of the calculations I learned from him a long time ago with regard to 430.24 is as follows: If we had a 4-wire, three-phase system that had a 5 HP three-phase motor and three 2 HP single-phase 120 volt motors on the same feeder, what would be the minimum ampacity (Tom Henry Step 5)? I've always gone on the solution that the single-phase motor has the largest FLC: 24 amps x 1.25 = 30 amps x 16.7 amps for the three-phase motor only. The rationale was that only the three-phase motor was on the same LINE. I just had a class where someone pointed out that 430.24 uses that language of "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..." Therein became a discussion of what is the meaning of "GROUP" is. Without another discussion of definitions according to one of our nation's Presidents, it's been my contention that since it is a 4-wire, three-phase system, we need to look only at what motors are on the same LINE. I was challenged on this, specifically on the language for the "GROUP." Is it the intention of the Code to make the "GROUP" be of the specific phase, or, all motors? I've checked back about 8 years on ROP's and proposed changes. I know there was an intent for 430.24 to include other incidental loads according to Section 220. Am I wrong here?