# of CCC in conduit / Ampacity check of THWN-2 in 4 CCC 18" underground PVC conduit

[SparkyGriswald]

Having difficulty discerning NEC Table 690.31(A)(3)(1).

I am planning on 2 MI solar branches (20 feet apart) running 12 AWG Enphase Q cable to 8AWG THWN-2 (2 CCC each branch) via PVC sch 80 above grade then to sch 40 at 18" below grade to a pull point where they will be joined (4 CCC in one sch 40 PVC for around 40 more feet to an enphase combiner box on the house. However, In reading 690.31(A)(3) I see a reference to "The ampacity of 105°C (221°F) and 125°C (257°F) conductors shall be permitted to be determined by Table 690.31 (A)(3)(1). " The table goes on to state " Not More Than Three Current-Carrying Conductors in Raceway, "
1. Does this section not even apply to me because I am using THWN-2? (And therefore running 4 CCC would be fine, as long as I use the fill derate)
2. If it does apply, does that mean that I need to have 2 seperate PVC conduits from the pull point to the Combiner box on my house, so that the max CCC is 2 in each conduit?

Thanks!

 

[DIYrich]

I'm guessing you are using 75c rated wire, so would that section apply?

 

[SparkyGriswald]

Correct the THWN-2 is actually 90C rated wire - however the breakers attached are rated at 75C

 

[kayakingphotos]

I'm no expert, but does your code reference just deal with wiring for DC conductors and not AC?

8 AWG 90 degree wire is rated for 55 amps. If you have 4 current carrying conductors you multiply that by 80% giving you an ampacity of 44 amps.

Since you are using 12 AWG Enphase cabling, you need to use a circuit breaker no greater than 20 amps.

Four 8 AWG current carrying conductors in a conduit protected by a 20 amp circuit breakers is well within code requirements (NEC 310.15)

Unless I'm totally missing what you are trying to do......