Conduit routing (off the roof) and sizing.

[t5800512]

Okay, I have my system purchased and ready to install. I think I have it pretty much figured out with just a couple questions.

I will be installing two Enphase M215 sub-systems. There will be 16 inverters on one trunk cable, and 11 on the other. I plan to run 10 gage wire to from both of them. So I will have eight 10 gage wires running through one raceway. NEC 2011 limites 3 or more wires to 40 percent of the interior raceway volume. Is there a table somewhere that can help me determine the diameter of the conduit I need? I'm not sure how to calculate the volume of the eight wires. If you are wondering, I plan to run the 6 gage solid copper grounding wire outside the raceway. It will be zip tied to the conduit and run to a separate grounding rod. The green grounding wire from the enphase trunk cable will be routed back to the ground at the main service breaker box.

My second question is now to run the wiring off of the roof. My meter and main breaker panel is right under the solar panel array. Really just to handy. I have been planning on running the conduit over the edge of the roof, back up under the soffit to the wall, and down to the combiner A/C sub-breaker box (with two double pole 20 amp breakers). There will be an three pole A/C Disconnect after that before the wiring goes into the main breaker panel.

So, does anyone see a problem with my plan? I'm not exactly sure how to run the conduit off the room. The room has about a 20 degree angle to the ground.

Guys, I appreciate your thoughts on this.

[Naptown]

In your case you will only need 6 wires from the roof + a #6 ground outside the conduit. You can use a common ground and neutral on two enphase circuits. (the neutral is used only for communications) 3/4" conduit will be plenty big
Next up is why the additional disconnect you have 2 2 pole circuit breakers that will serve as the utility disconnect so an additional one is not needed unless this is a line side tap and the panel is located inside (in that case you will need only a 2 pole disconnect inside)
Lastly that is what pipe benders are for to bend the pipe to 20^o

[t5800512]

Hey Naptown, thank you for the reply.

For some reason I was thinking I needed to have three poles for the A/C Disconnect. I guess, if two is good, three must be better kind of thing. Using a two pole will save me a few bucks, so thank you. The disconnect is the only thing I don't have yet. I ordered a 30 amp three pole from a company named SolarConduit.com. It turned out to be a "Rip Off" website, so stay clear of them. I may be able to pick one up at a bigger Home Depot.

I think I prefer to run 8 wires because my ground off the roof is going to be strictly a GED and go to a grounding rod. But I;m hoping I can get by with no larger than 3/4 conduit. By the way, I'm planning on using PVC. I think that is okay with A/C only. But I just can't picture how it will be coming off the low sloped side of the room. By the way, I would also like to hold the conduit raceway off of the room a couple inches. Any Ideas?

I have been watching folks view this thread and wondering why no one was responding. You are a great forum member and seem to be very knowledgable. So thank you again.

[Naptown]

Hey Naptown, thank you for the reply.

For some reason I was thinking I needed to have three poles for the A/C Disconnect. I guess, if two is good, three must be better kind of thing. Using a two pole will save me a few bucks, so thank you. The disconnect is the only thing I don't have yet. I ordered a 30 amp three pole from a company named SolarConduit.com. It turned out to be a "Rip Off" website, so stay clear of them. I may be able to pick one up at a bigger Home Depot.

I think I prefer to run 8 wires because my ground off the roof is going to be strictly a GED and go to a grounding rod. But I;m hoping I can get by with no larger than 3/4 conduit. By the way, I'm planning on using PVC. I think that is okay with A/C only. But I just can't picture how it will be coming off the low sloped side of the room. By the way, I would also like to hold the conduit raceway off of the room a couple inches. Any Ideas?

I have been watching folks view this thread and wondering why no one was responding. You are a great forum member and seem to be very knowledgable. So thank you again.

Glad to hear that your ground will have it's high school equivalency diploma. However it will fail inspection if you permit this installation.
There are two grounds you need to run to the array and connect. One is the EGC or equipment grounding conductor and is a #10 that will connect to the two green wires of the two engage cables.
You will also need to run a single neutral (white or gray insulated) wire that will connect to the two white wires of the engage cables.
The green and white wires will connect to the neutral and ground bars in the panel.
Lastly you will need a #6 copper GEC or grounding electrode conductor or Bonding wire as it is referred to also. This will bond all rails, inverters, and modules. (WEEB clips are acceptable to the NEC for bonding the modules and inverters to the rails)
Now this wire will depending on your AHJ either tie into the ground buss in the panel or connect to the ground wire that goes to the service ground conductor. If you splice this wire at any time it will need to be an irreversable splice (crimped splice) This will require a hydraulic crimper.

[inetdog]

I think I prefer to run 8 wires because my ground off the roof is going to be strictly a GED and go to a grounding rod. But I;m hoping I can get by with no larger than 3/4 conduit. By the way, I'm planning on using PVC. I think that is okay with A/C only. But I just can't picture how it will be coming off the low sloped side of the room. By the way, I would also like to hold the conduit raceway off of the room a couple inches. Any Ideas?

Make sure that the PVC you use is UV resistant or be ready to paint it or otherwise wrap it.
Wood blocks as spacers are low tech but work just fine.
The temperature benefits of lifting it off the roof reach a point of diminishing returns at about 6 inches. Are you more concerned about not collecting leaves and debris?
With PVC, you can't easily bend it, and two tight elbows to produce an angle would make it very hard to pull the wires. Maybe a short section of flex to go around the edge of the roof and to the wall would be easiest for you.

[t5800512]

Hey Naptime, I think we are on the same page with two possible exceptions. I sure don't want to fail my inspection, and that is why I'm trying to learn everything I can. So you are saying to combine the neutral white wires on the roof? I can do that, but is that necessary, or prefered? I assume I would need to go to a heavier gage wire If I do that. But then again, it is just the neutral and won't carry much current. The other difference is the GED grounding method. I was going to run it to a grounding rod. This is my thread on this subject: http://www.solarpaneltalk.com/showth...top-to-bottom). I'm still waiting for someone to rip me a new one on this thread, but good so far.

The problem with the grounding rod is that local jurisdiction is still on NEC 2008. So that will make this interesting. I think my inspectors are forward looking and will be okay as long as I comply with the 2011 NEC. Just the same, I was going to keep the grounding cable rolled up and uncut at the grounding rod just in case. So please don't take me wrong, I respect your opinion and want to learn from you.

Inetdog, thank you for your input. I had not considered wooden block. You are right, low tech, but actually a pretty good idea. I think I will get a treated 2 x 4, cut it into blocks and use that. I can use the conduit clips to attach the blocks to the raceway. I like that idea. No, not leaves, I just want the conduit lying on the asphalt roof. I want it to look professional and I think keeping it off the roof is a good idea.

I was going to use the gray PVC that is made for electrical conduit. I think it is UV stabilized, but I need to find out for sure. I did pick up some 3/4 flex conduit thinking of using it to get off the roof like you said. The alternative I have considered is the little inline conduit junction boxes that you take the end off for pulling wires. For the live of me, I can think of the name of them, but they have a screw on cover with a gasket to keep them water tight. But there is still the 20 degree angle to deal with. Maybe a combination of the conduit and the wire pull box. Hey, thank you for the ideas. You guys are great!

[Naptown]

Sorry but the #6 must be bonded to the building grounding electrode conductor. yes you can drive and connect additional ground rods but these must also be bonded to the buildings grounding electrodes. There is one exception but it does not apply in your case.
There is nothing wrong with running individual ground and neutral wires to the inverter circuits. If you were using Romex you would have to. (note The code allows this but many jurisdictions do not allow this to be used) The reason in your case is to allow a smaller pipe size. With 8 conductors you may need to go to a 1" conduit.

[t5800512]

Thank you Naptime! I really do appreciate your feedback.

To be honest, I had not considered dropping one of the neutral wires. It would be easy to do. I'm planning on securing an aluminum junction box to a rail and connecting the enphase trunk cable and the #10 wires inside of it. I'm planning on using appropriate sized wire nuts for the connections. I can probably combine the EGC green wires so I will only have one of them also. So is that how you got the 6 you originally mentioned.

I'm going to cut 6 one inch pieces of the #10 THHN wire and lay it into the conduit to see how it looks. I think I can judge if it is over 40 percent of the volume by just looking at it. I really hope I don't have to go to one inch conduit. If I do, I won't be able to use the flex conduit going off the roof. I will let you know how it looks.

[t5800512]

Okay, I did my little test. It looks like I can get 7 ten gage THHN wires into a 3/4 inch PVC conduit. I tried six and it looked like there was room for one more. So even though I only need 6, I added one more and it dropped down in a slot between the 6 already there. Looks to be about 40 percent full with 7 wires. If I add an 8th wire, it is too much, as it sits on top of the others. I still think there must be a table for this somewhere. But I now know that I can use 3/4 inch conduit with 6 wires.

I still plan on running the 6 gage GEC on the outside of the conduit. I will zip-tie it to the raceway unless I can find something better. I would rather not use zip-ties because I'm sure they will not last 20 years outside.

[Naptown]

there is a table in the NEC for wires in a conduit
You're right about the zip ties especially the white ones (the black ones last longer)
What we do is slip the ground wire between the wall the pipe and the pipe clamp so it is captive in that little slot.
THHN is not rated for wet locations
it will need to be THHN2 or THWN2

[Naptown]

You can actually fit 9 #10 wires in a 3/4 PVC sch 40 conduit

[SunEagle]

You can actually fit 9 #10 wires in a 3/4 PVC sch 40 conduit

Better use some of that blue wire pulling gel to slip them through.

[t5800512]

Oh no. I have already purchased my wiring, which is THHN. If the wire is in a sealed PVC conduit, does it matter?

[SunEagle]

Oh no. I have already purchased my wiring, which is THHN. If the wire is in a sealed PVC conduit, does it matter?

THHN type insulation is really for dry type or indoor work. THWN is what is required for outside or possible wet locations.

How is your wire "sealed" in the conduit?

[t5800512]

Hey SunEagle, welcome to the discussion.

I will be using compression strain relieve fittings to bring the enphase trunk cable into the aluminum wiring junction box. The junction box has a sealing cover, and connects water tight to the PVC conduit raceway. I think it will stay dry. I can even use some silicon on the fittings.

But if it won't pass the inspection, all that does not matter.