In an ec&m article they have some examples of calculating parallel conductors. 3 conduits each having a a set . They took the size of the conductor x 3 . Since it was more than the allowance permitted by the table a 12.5% adjustment was added. This answer was then divided by 3 and sized accordingly. Was that last step needed?
Parallel grounded conductor
- Thread starter Djelite
- Start date
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- Location
- New Jersey
- Occupation
- Journeyman Electrician
Are trying the size the minimum required grounded conductor is 3 separate service raceways?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I'm taking an educated guess here based on the information given. The reason that they divided by 3 is because you have 3 parallel sets of conductors. For example lets say you have 3 set's of 600 kcmil for a 1200 amp service in 3 raceways. 3*600=1800 kcmil which exceeds the values in T250.66. So your minimum grounded conductor is sized by 1800*12.5%. That would be for a single raceway. 250.102(C)(2) tells you that the grounded conductor for each service raceway can be sized according to the conductors in each raceway. 1800/3=600 kcmil in each raceway so the minimum size grounded conductor would be #1/0 in each raceway.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Coincidentally, the minimal paralleling size.
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