Talked to an Electrical Inspector and 3 P.E.'s, getting different answers
If an underground service from a delta high leg transformer feeds a fusible disconnect in a single existing conduit, and 2 of the conductors ( a phase, c phase, parallel 700 mcm ) must all of the conductors in the same conduit be parallel also, even if the loads are different ? Calculated loads are different.....
A & C phases 2 pairs of 600 mcm ( existing ) for 700 amp class L fuse
B Phase 1 - 250 MCM for 250 amp class L fuse
1 - 700 mcm for neutral ( meets calculated neutral load )
in 1 existing 4" conduit.
Going over 6 current carrying conductors will cause me to derate to 70% instead of 80% where the conductors will no longer fit and will require an additional conduit to be installed under an existing building or 2 new conduits around the building perimeter, abandoning the existing one. The situation is existing, as If it were new I would have run 2 parallel conduits from the beginning.
I also have to consider the neutral having a lesser ampacity than the A & C phases, even though the neutral calcs would allow a smaller mcm than the ones on A & C phases...
I will have an electrical P.E. review my plans and wonder if he has the power to approve this before presenting plans to the LJHA.
Same as my earlier post today but in simpler terms...
Thanx, dhsvcs
If an underground service from a delta high leg transformer feeds a fusible disconnect in a single existing conduit, and 2 of the conductors ( a phase, c phase, parallel 700 mcm ) must all of the conductors in the same conduit be parallel also, even if the loads are different ? Calculated loads are different.....
A & C phases 2 pairs of 600 mcm ( existing ) for 700 amp class L fuse
B Phase 1 - 250 MCM for 250 amp class L fuse
1 - 700 mcm for neutral ( meets calculated neutral load )
in 1 existing 4" conduit.
Going over 6 current carrying conductors will cause me to derate to 70% instead of 80% where the conductors will no longer fit and will require an additional conduit to be installed under an existing building or 2 new conduits around the building perimeter, abandoning the existing one. The situation is existing, as If it were new I would have run 2 parallel conduits from the beginning.
I also have to consider the neutral having a lesser ampacity than the A & C phases, even though the neutral calcs would allow a smaller mcm than the ones on A & C phases...
I will have an electrical P.E. review my plans and wonder if he has the power to approve this before presenting plans to the LJHA.
Same as my earlier post today but in simpler terms...
Thanx, dhsvcs
