Dark Sparky
Member
- Location
- USA
- Occupation
- Electrical Engineer
I'm reviewing a concept proposed by an electrical contractor. There is an existing 480V, 3 phase, 400A distribution panel DP1, fed from switchboard MDP via a 400A breaker in MDP. Proposal is to intercept (more below) that feeder via a new J-box just below DP1. Then run 2 sets of 4-#3/0+G in 2-1/2" conduit immediately to a 400A enclosed circuit breaker (located near the intercept). Continue from that breaker about 175' to a new 400A distribution panel DP2.
1. Because the ampacity of the feeder (2x200A=400A) isn't exceeded by the rating of the upstream 400A overcurrent device, I understand that the feeder conductors are NOT considered to be tap conductors, per the definition of tap conductor in 240.2. (The intercept below DP1 is not considered a tap.)
2. Because the feeder intercept (point of supply) isn't considered a tap, I understand that there is no rule regarding additional overcurrent protection, and the new 400A enclosed circuit breaker could be anywhere convenient (in other words, it does not need to be a given distance from the feeder intercept).
3. I have no issue with the volt drop, even at a full 400A load.
4. The proposed ground wire size for the parallel feed was unclear. Per 250.122(G), etc., I would supply a #3 ground in each conduit (full-sized ground in each conduit, sized for 400A upstream breaker.)
Please let me know if anything above needs more clarification, is incorrect, or questionable. Thanks in advance as always!
1. Because the ampacity of the feeder (2x200A=400A) isn't exceeded by the rating of the upstream 400A overcurrent device, I understand that the feeder conductors are NOT considered to be tap conductors, per the definition of tap conductor in 240.2. (The intercept below DP1 is not considered a tap.)
2. Because the feeder intercept (point of supply) isn't considered a tap, I understand that there is no rule regarding additional overcurrent protection, and the new 400A enclosed circuit breaker could be anywhere convenient (in other words, it does not need to be a given distance from the feeder intercept).
3. I have no issue with the volt drop, even at a full 400A load.
4. The proposed ground wire size for the parallel feed was unclear. Per 250.122(G), etc., I would supply a #3 ground in each conduit (full-sized ground in each conduit, sized for 400A upstream breaker.)
Please let me know if anything above needs more clarification, is incorrect, or questionable. Thanks in advance as always!