positive and negitive wires in seperate conduits

[collin estep]

do positive and negitive wires need to be in the same conduit or can they be ran seperate? We are doing a ballast mount on a roof and all the positives are ran on one side of the array and all the negitives on the opposite side. we are using black corrgated split tubing from row to row which is about a 16" seperation but all the positives pass thru the 16" tubing and like wise with the negitives. I know with AC they must be in same conduit but not sure if that applys for DC?

 

[Dennis Alwon]

I don't see 300.3 (B) as giving an exception for DC

 

[Besoeker]

do positive and negitive wires need to be in the same conduit or can they be ran seperate? We are doing a ballast mount on a roof and all the positives are ran on one side of the array and all the negitives on the opposite side. we are using black corrgated split tubing from row to row which is about a 16" seperation but all the positives pass thru the 16" tubing and like wise with the negitives. I know with AC they must be in same conduit but not sure if that applys for DC?

Regardless of possible code violations, it is a bad idea.
I've seen it done with DC drives where the positive was made through one glandplate in one enclosure and the negative from another.
It buckled the panel doors.
Think electromagnet.

 

[Marvin_Hamon]

I think it is a bit of a gray area for PV source circuits inside the PV array. Once the circuit leaves the array all the conductors and the EGC need to be in the same conduit.

Inside the array it is sometimes not possible to match up a positive with a negative conductor everywhere. Unmatched conductors run from module to module in a string and often an unmatched conductor has to be home run the full length of a string before it can be paired up with the other conductor. So for instance, if I were making up a string out of modules in different rows I might have to take a single conductor and put it in conduit to get it to the other row to pickup all the modules in a string. At some point I have to bring the positive and negative for that string back together before leaving the array.

I would say running all the positive conductors down one side and all the negative conductors down the other side of the array would be an unusual design and not one I would do, it's just not my idea of a best practice taking into account DC combiner locations and trying to equalize the lengths of the PV source circuits. Maybe for a small array it would work.

 

[jaggedben]

I would say running all the positive conductors down one side and all the negative conductors down the other side of the array would be an unusual design and not one I would do,.

I agree. If it's simply the case that each row is one string, and the combiner is to one side of the array, there is no meaningful change in the amount of wire used if one simply runs the negatives (or positives) along the rows under the modules to the same side as the other conductors. Then one also needs fewer conduits because they can all be on one side of the array. Another advantage may be that it's easier to keep track of the source circuits for each string if you keep the conductors together. I have a difficult time imagining what would make it worth the trouble to have all negatives remote from all positives.

 

[BillK-AZ]

Some of the PV modules have leads that are long enough to allow "wave" wiring where-in module 1 is connected to module 3, etc. to the end and then the string returns to the starting end by connecting the even numbered modules.

This method results in both the positive and negative connections at the same end of a row so they can be paired if desired. Less wire is needed.

Some modules have leads just a tad too short to do this, so check before designing an array this way.

 

[Marvin_Hamon]

Never heard of wave wiring. Great idea if the leads are long enough. Thanks Bill.