Suggestions for cable trays instead of conduits for roof mounted pv arrays

Anode

Member
Location
Washington, USA
Suggestions for cable trays instead of conduits for roof mounted pv arrays to house either dc or ac circuits on the roof, exposed to sunlight.

Does anyone have any products they like? Recently heard Bill Brooks suggesting that EMT and couplings come apart over time on the roof. He suggested looking into cable trays. And even though cable trays cost a little more, they are easier to install, and so therefore they wash somewhat.

Does anyone have any suggestions on cable tray products for this?
 
We did 7 350KW rooftop systems last year that were cable tray for the inverter outputs. When I first learned of how the job was designed, I thought the tray would be the cat's meow, however after installing it, I do not at all think its the way to go. It might seem quick but its quite labor intensive: logistics of handling, transport, and moving the stuff around; transitioning in and out of the tray, stripping tray cable is a bear. As far as cost, im sure its not cheap (i dont know numbers from these jobs) and tray cable will likely be special order. We also wasted a bunch of TC because it came in 500 foot spools and often are runs were such that there was a big piece left that was too short for anything.

I could see using pieces of it where string wires cross walkways, or a trunk line for the sting home runs. Part of my bad experience may just be the way these systems were designed: by PV people who have never been electricians and do things like scatter string inverters all over the roof. Doesn't that look all neat and tidy on paper.

My current thinking about the best way to do a commercial rooftop system is to place the inverters (and I prefer fewer inverters instead of a zillion) all in a row near the AC gear/combiner and pipe up to them. Use some cable tray for a trunk line from the inverters to get into the array or down the middle, etc. Hopefully the racking system has trays or other wire management built into it so the stings can be quickly and effectively run through the array as needed so we save time and dont have to use zip ties. Finally, cross you fingers that 1500 V PV goes mainstream ASAP!

I dont think EMT comes apart on roofs, that is hogwash. As Iwire pointed out a while back on this subject, EMT has been used on roofs long before PV was around. EMT failures on roofs are from poor workmanship.
 

Carultch

Senior Member
Location
Massachusetts
My current thinking about the best way to do a commercial rooftop system is to place the inverters (and I prefer fewer inverters instead of a zillion) all in a row near the AC gear/combiner and pipe up to them. Use some cable tray for a trunk line from the inverters to get into the array or down the middle, etc. Hopefully the racking system has trays or other wire management built into it so the stings can be quickly and effectively run through the array as needed so we save time and dont have to use zip ties. Finally, cross you fingers that 1500 V PV goes mainstream ASAP!
.
If your inverters are not within 10 feet of the array, then you can't take credit for the inverters solving the rapid shutdown problem.
 

Carultch

Senior Member
Location
Massachusetts
We haven't had to deal with rapid shutdown yet, but I envision the inverters mounted within that 10 feet for compliance without additional equipment.
Per 2014, yes.
Per 2017, they are going to require equipment that is specifically listed for rapid shutdown, as opposed to complying with equipment that is listed in general, yet not specifically listed for rapid shutdown. And they will tighten up the 10 ft limit, so I doubt you'll be able to get an inverter in the required place.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Hopefully your AHJ interprets that as within 10' of the entire array rather than the particular subarray that feeds a particular inverter.
We have had some success in doing that; the point is (I surmise) not to have conduit carrying CCC's extending more than 10' from the array.
 

Carultch

Senior Member
Location
Massachusetts
We have had some success in doing that; the point is (I surmise) not to have conduit carrying CCC's extending more than 10' from the array.
So given separate "islands" of solar that are 20 ft apart, does this mean that you could have all the rapid shutdown components located adjacent to just one of the "islands"? Since all points in that 20 ft gap are within 10 feet from at least one of the arrays.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
So given separate "islands" of solar that are 20 ft apart, does this mean that you could have all the rapid shutdown components located adjacent to just one of the "islands"? Since all points in that 20 ft gap are within 10 feet from at least one of the arrays.
I don't know; that may be a judgement call for the AHJ. In the cases I have dealt with it was a single array with multiple inverters all grouped together within 10' of the array. The home runs to the inverters were all under the modules within the array, and that was OK.
 

pv_n00b

Senior Member
Location
CA, USA
There is a difference between "cable tray" and cable support systems. Snake tray for instance is a cable support system and not cable tray. Using cable tray involves applying the cable tray provisions of the NEC, article 392, that might make installation more demanding than you want. So I recommend Snake Tray for C&I. It's pretty handy. I have heard pushback from people who think that the conductors should not sit out in the sun, even if rated for sun exposure. For that reason you can get tray covers.
 

Carultch

Senior Member
Location
Massachusetts
There is a difference between "cable tray" and cable support systems. Snake tray for instance is a cable support system and not cable tray. Using cable tray involves applying the cable tray provisions of the NEC, article 392, that might make installation more demanding than you want. So I recommend Snake Tray for C&I. It's pretty handy. I have heard pushback from people who think that the conductors should not sit out in the sun, even if rated for sun exposure. For that reason you can get tray covers.
So because of silly semantic word games, you can avoid the NEC rules for cable trays, just by calling it a "cable support system"?
 

Anode

Member
Location
Washington, USA
There is a difference between "cable tray" and cable support systems. Snake tray for instance is a cable support system and not cable tray. Using cable tray involves applying the cable tray provisions of the NEC, article 392, that might make installation more demanding than you want. So I recommend Snake Tray for C&I. It's pretty handy. I have heard pushback from people who think that the conductors should not sit out in the sun, even if rated for sun exposure. For that reason you can get tray covers.
Thank you for the suggestion. I will look into this product.

I sort of share the same sentiments with not having exposed conductors in sunlight.
 

Anode

Member
Location
Washington, USA
Here are some options:

LeGrand

Eaton

Snake Tray

Blue Oak Energy has 1 GW of PV in operation. They prefer cable tray for rooftop systems (in part due to the simplified O&M).
Thank you very much for the suggestions.

To speak to some of the other replies as well, I think that because we are more focused on quality of our installations we liked the idea of a cable tray to house rooftop conductors. Especially if the advice is coming from someone like Bill Brooks, we are going to strongly consider a recommended best practice or alternative.

I have not yet seen for myself any of our installations that have had conduit separate on the roof, and I can say that many of our commercial installations were done with rigid and threaded couplings, but it is always best to entertain ideas on how to do a better install, even if that may come at a slight premium to the cost. Then again, solar and even solar installations have become so commodified these days it seems you have to either cut corners on the material side, or ask more of your installation team to finish projects faster. Double edged sword.

Anyway, thank you all for the suggestions.
 

pv_n00b

Senior Member
Location
CA, USA
So because of silly semantic word games, you can avoid the NEC rules for cable trays, just by calling it a "cable support system"?
I should recommend adding that as the official description of the code, "National Electrical Code, a silly semantic word game. Fun for the whole family!"
 
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