panhandle444
Member
- Location
- oklahoma
What's the proper way to bundle pv homeruns under an array? Keep each positive and negative together if possible? Is derating the same for DC as with AC? Thanks
No derating except for temperature is required for conductors that are not run in a raceway.
Is that exclusive to PV circuits? Because that is not the case with standard circuits.
However considering the typical ISC and conductor size of a string, i would take a whole bunch of conductors for derating to kick in.
What's the proper way to bundle pv homeruns under an array? Keep each positive and negative together if possible? Is derating the same for DC as with AC? Thanks
Is that exclusive to PV circuits? Because that is not the case with standard circuits.
(This was so similar I posted my response to the wrong comment...)
My mistake. But it's never arisen as an issue for me. Considering that one could use the free-in-air table, and that one will have already sized wire-gauge in the raceway for any derate, you'd pretty much never have a higher derate on the array than in the homerun in a raceway.
If there is nothing in 690 changing things the normal rules of derating apply.
If they are bundled they are not free air conductors
So if I have just one conductor clipped to a rack, it counts as a free air conductor? But the instant I bundle a second one with it, it now has to have the ampacity from 310.15(B)(16)?
Yeah, I have a bit of a problem with applying a derating for this. If only because clearly this particular question was never considered when making these code sections.
(3) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a
Raceway or Cable. Where the number of current-carrying
conductors in a raceway or cable exceeds three, or where
single conductors or multiconductor cables are installed
without maintaining spacing for a continuous length longer
than 600 mm (24 in.) and are not installed in raceways, the
allowable ampacity of each conductor shall be reduced as
shown in Table 310.15(B)(3)(a). Each current-carrying conductor
of a paralleled set of conductors shall be counted as
a current-carrying conductor.
Where conductors of different systems, as provided in
300.3, are installed in a common raceway or cable, the
adjustment factors shown in Table 310.15(B)(3)(a) shall
apply only to the number of power and lighting conductors
(Articles 210, 215, 220, and 230).
For PV source circuits most designers use #10; the ampacity of #10 is so much higher than Isc for a string that this is seldom an issue.Are you permitted to use the free air table for wires clipped to a racking system or in a cable tray? The NEC doesn't specify how to adjust ampacity for listed PV wire of sizes such as #10 in a cable tray.
It's important only in the calculations if the designer shows his (or her) work. I usually do but I often wonder if anyone but me even looks at that stuff.To be fair, Jaggedben is usually on the right side of the law. Just not in this case. Bundled cables are subject to ampacity reductions.
@ggunn is right, 10AWG source circuit conductors likely have the required ampacity even after factoring in the conditions of use.
To be fair, Jaggedben is usually on the right side of the law. Just not in this case. Bundled cables are subject to ampacity reductions.
For PV source circuits most designers use #10; the ampacity of #10 is so much higher than Isc for a string that this is seldom an issue.