Underground Raceway

[haj]

I am installing a 2 string 6kw array on an outbuilding the dc current will run back to the inverter near the main panel through an underground conduit.

There will probably be a second inverter installed next year to a three string array on the same outbuilding. Can all of the DC share the same raceway?

 

[BillK-AZ]

Consider Table 310.15(B)(3)(a)

Consider Table 310.15(B)(3)(a)

You should consider Table 310.15(B)(3)(a) adjustment factors for the number of current carrying conductors in the conduit.

I may be lower cost to run two smaller conduits now instead of one larger conduit sized for the reduced ampacity of 10 current carrying conductors (5 strings). The conductors you install now for two strings may not be suitable if more current carrying conductors are added later.

 

[ggunn]

I am installing a 2 string 6kw array on an outbuilding the dc current will run back to the inverter near the main panel through an underground conduit.

There will probably be a second inverter installed next year to a three string array on the same outbuilding. Can all of the DC share the same raceway?

There is no problem with DC conductors from different systems sharing a raceway, but as was pointed out above, pulling more current carrying conductors through existing conduit may change the conductor fill derating of all the conductors (NEC 2008 Table 310.15 (B)(2)(a)) to the point where you have to replace the existing ones. If you plan ahead for it, though, it can be done.

 

[barclayd]

Trying to pull additional conductors into an existing, operational, partially filled conduit is not always successful.
If you already have to trench anyway, a couple additional conduits will not appreciably increase the cost.
I would add enough conduits to cover the planned addition, and maybe even an unplanned addition.
db

 

[haj]

I found what causes my confusion in 690.4.B. Am I to take it that the 2 inverters are sub-sytems?

 

[jaggedben]

I found what causes my confusion in 690.4.B. Am I to take it that the 2 inverters are sub-sytems?

Strictly speaking if you have two inverters you have two solar systems. The word 'sub-system' has no meaning in the NEC as applied to solar.

In the 2011 code, 690.4 B was revised and expanded and it now clearly allows PV source and/or output circuits from different PV systems (i.e. inverters) to occupy the same raceway, provided some conditions are met. In my opinion there is no reason that having all the DC circuits occupy the same raceway would be a code violation, although your AHJ may disagree if you are on an earlier code cycle or if there are local requirements or expectations. But as others have said, it is probably more practical to run multiple raceways, especially for the potential later expansion.