PV Wire In Cable Trays

sketchy

sketchy

Senior Member
Location
MN
Help me understand 690.31(C)(2). It says that 1) all single conductors shall be installed in a single layer 2) pairs (positives and negatives of the same string) can be stacked and 3) the sum of all the single conductor diameters must be smaller than the width of the cable tray. Our #8 PV wire's diameter is .331 in. and if I use a 24" wide cable tray the math says I can have 72 wires in it. The issue I'm having is if I was to stack each string, black on top of red, and laid each string right next one another, I would only be using 1/2 of the cable tray's width per #3. That seems to contradict being able to stack wires. In my POV, I should be able to have 72 strings because they'll be stacked on top of each other. This job is over 1 MW and the less cable tray the better. Thoughts?
 
Just reading that section in isolation, 690.31(C)(2)3) is very clear. That limits the number of wires, and there's no way around it.

Then you can install that number of conductors as a single layer with the conductors touching. Or if you choose to stack +/- together, it would make sense to space those stacks out, to improve the air flow. Two layers with all the conductors touching does not comply with (3), it would be twice the number allowed.

Cheers, Wayne
 
This condition only applies for ladder-style cable trays, where it's uncommon that you'd even use that type of tray for collecting individual string wires anyway. Typically, ladder-style cable trays are for combiner-output conductors.

Basket-style cable trays, allow you to fill with small, string-level wires, whatever you can fit in the cross section. I.e. up to 50% fill by area. And 50% fill by area is going to "look" full, since it's impractical to lay the wires with perfect circle packing.
 
This condition only applies for ladder-style cable trays, where it's uncommon that you'd even use that type of tray for collecting individual string wires anyway. Typically, ladder-style cable trays are for combiner-output conductors.
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Basket-style cable trays, allow you to fill with small, string-level wires, whatever you can fit in the cross section. I.e. up to 50% fill by area. And 50% fill by area is going to "look" full, since it's impractical to lay the wires with perfect circle packing.
Click to expand...
We're using wire mesh tray i.e. basket style. What code section are you referring to that allows 50%?
 
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