I'm getting confused with this part. Art 250-30 (8) (B) When do I size the Service "Neutral" or Grounded Cond. by the sum of the Paralell conductors kcmil ?, As opposed to the size of the largest phase conductor in the raceway ?. It says size to the largest conductor when installed in two or more raceways wouldn't that mean almost always as with 2-3-4 raceways and sets of a-b-c ,Grounded and Ground conductors in each set or raceway ?. Not real familair with Paralell. Thanks
Need help quick.,Paralell Grounded Cond. Sizing
- Thread starter tunny
- Start date
- Status
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Read the last sentence (starts with "Where installed in two or more ...") of
250.30(A)(8)(b) Parallel Conductors.
250.30(A)(8)(b) Parallel Conductors.
First, if you are talking service, the appropriate article is 250.24(C)(2).
250.30(A)(8)(b) is for separately derived systems.
Both say essentially the same thing... but because they use slightly different language breeds some confusion.
...and the only time you actually size the grounded conductor by these requirements is if the grounded conductor would otherwise be permitted to be smaller than the size of the GEC or 1/0, whichever is larger, such as downsizing the neutral to handle only the max imbalance load on the system.
250.30(A)(8)(b) is for separately derived systems.
Both say essentially the same thing... but because they use slightly different language breeds some confusion.
...and the only time you actually size the grounded conductor by these requirements is if the grounded conductor would otherwise be permitted to be smaller than the size of the GEC or 1/0, whichever is larger, such as downsizing the neutral to handle only the max imbalance load on the system.
O,k, still a little confused., Mike holts Grounding and Bonding book says Para Neutral Cond.,Where service cond are paralelled, a neutral cond. must be installed in each raceway and it must be sized in accordance with 250-66 "based on the area of the largest service cond in the raceway and not smaller then 1/0 .Meaning only one of the phase cond. I'm assuming. Then there's a qeuston what min size srevice neutral conductor is required for a 480v, 3 phase service installed in "TWO" raceways where the ungrounded cond. service cond.in each raceway are 350kcmil and the max unbalanced load is 100 amps. The answer is 1/0...Since its two or more raceways wouldn't the answer be the sum of the phase cond in one raceway times two sets be , 350 kcmil & 2 sets= 700kcmil as stated in the last sentence in 250-30 (8) (b) then size by 250-66..And even more confusing the picture shows two raceways with only two phase conductors red and black and neutral in each raceway. I used to believe two or more raceways you sum the kcmil of the amount of phase a or phase b or phase c,now I'm getting mis info from everyone I ask ,so now I'm confused two days before the test. Please help and explain in detail please I'm getting steered all over the place.....Thanks,extremley frustrated ....
O,k, it's all making sense now found two examples on with single conduit and one with two or more in my old Scallcups electrical design book from school back in the day.Just never saw or heard of Paralell run sevice run in one conduit. Like I said not much exp with Paralell but I have it all down now, Grounded, Gec, Mbj, Sbj, Egc ,Line and supply side, sepertley derived sys, seperate bldg, etc... Thank's again guys you helped me out of a big one...
Parallel runs in one conduit are normally based on (a) comparative cost (wire cost + one less conduit---not always less expensive, but can be); (b) ease of working smaller conductors.
When designing you have to be careful, however, because of derating (310.15)(b)(2).
When designing you have to be careful, however, because of derating (310.15)(b)(2).
- Status