code questions, direct bury vs conduit for outdoor rated wire (THWN-2)

[df0rster]

You're welcome and I did mean to cut you off. The reason is that you mentioned two sub-panels in/on the house each with its own grounding electrode. That's just plain dangerous.

Not 2 subpanels. 1 is my main panel w/ an outdoor subpanel. I can have an electrician look at it, but I also want to understand the proper methods myself.

So do you mean it is dangerous to install separate grounding electrodes at subpanels? I thought this would actually be safer. I'm not going to do anything without making sure its right and having an electrician look it over if necessary.

[DanS26]

I dont think its any More complicated than any other diy project Ive seen on this site. There are not outbuildings and sibpanels all over the place. The sub panel will be dedicated to the solar inverter and there is 1 outbuilding where the panels will go. This seems like a very common setup for grid tie solar, especially on this site.

But i do have 2 licensed electricians in the family that will help me. I just want to learn and understand everything myself first.

I also have installed a nice little off grid system on my shop before we built the house. It was a fun project and has been working flawless off grid for 2 years now.

I appreciate all all the useful feedback so far.

You're welcome and I did mean to cut you off. The reason is that you mentioned two sub-panels in/on the house each with its own grounding electrode. That's just plain dangerous.

[df0rster]

IMO you are outside the scope of a DIY solar site. You have a more complicated electrical setup with outbuildings and sub-panels all over the place.

My advice is to call in a qualified electrician and I don't mean a good old boy whose knows how to do "wirein".

I, nor the owners of this site, would not like to be responsible for advice misinterpreted and implemented incorrectly to cause property damage or personal harm.

Good luck and spend a few dollars with a professional to be safe and do the installation correctly.

I dont think its any More complicated than any other diy project Ive seen on this site. There are not outbuildings and sibpanels all over the place. The sub panel will be dedicated to the solar inverter and there is 1 outbuilding where the panels will go. This seems like a very common setup for grid tie solar, especially on this site.

But i do have 2 licensed electricians in the family that will help me. I just want to learn and understand everything myself first.

I also have installed a nice little off grid system on my shop before we built the house. It was a fun project and has been working flawless off grid for 2 years now.

I appreciate all all the useful feedback so far.

[DanS26]

The problem with bonding to my main service ground rod is its already underground and inside of a wall. (I think). I don't know exactly where that ground rod is but I know I can't get to it. There is also one at the power pole, which the Coop considers my service entrance where they have installed a 200amp main disconnect.

Where the array will be is a post frame shop 180' away from the main service (house) and I can install new ground rods there and bond them to each other, if more than 1 is needed. And I can also bury a GEC from that to the subpanel on the outside of my house where the inverter AC will tie in. I could even bond to another ground rod at the sub panel location.

IMO you are outside the scope of a DIY solar site. You have a more complicated electrical setup with outbuildings and sub-panels all over the place.

My advice is to call in a qualified electrician and I don't mean a good old boy whose knows how to do "wirein".

I, nor the owners of this site, would not like to be responsible for advice misinterpreted and implemented incorrectly to cause property damage or personal harm.

Good luck and spend a few dollars with a professional to be safe and do the installation correctly.

[df0rster]

No....bond from ground rods to ground rods......do not go above ground with this particular bonding......the GEC (grounding electrode conductor) bonding must be buried. Do not confuse this with equipment bonding which is accomplished with the EGC (equipment grounding conductor).

Don't know the structure of your ground mount.....but if you are using wood structure, you definitely need a couple of rods at the array. Metal posts in concrete are a good grounding electrode and are a good ground unless you have some kind of wood structure above. In any case bond these electrodes together UNDERGROUND.

The problem with bonding to my main service ground rod is its already underground and inside of a wall. (I think). I don't know exactly where that ground rod is but I know I can't get to it. There is also one at the power pole, which the Coop considers my service entrance where they have installed a 200amp main disconnect.

Where the array will be is a post frame shop 180' away from the main service (house) and I can install new ground rods there and bond them to each other, if more than 1 is needed. And I can also bury a GEC from that to the subpanel on the outside of my house where the inverter AC will tie in. I could even bond to another ground rod at the sub panel location.

[DanS26]

We don't have any AHJ in our small county. I'm not sure who I'd ask other than just following NEC.

In order to bond the electrodes I would have to run the proper grounding conductor (I think 6 awg minimum) from my array's grounding electrode into my subpanel at the house? Is it best to go ahead and have the grounding electrode at the array? It is about 180' away from my main panel and grounding rod.

Thanks!

No....bond from ground rods to ground rods......do not go above ground with this particular bonding......the GEC (grounding electrode conductor) bonding must be buried. Do not confuse this with equipment bonding which is accomplished with the EGC (equipment grounding conductor).

Don't know the structure of your ground mount.....but if you are using wood structure, you definitely need a couple of rods at the array. Metal posts in concrete are a good grounding electrode and are a good ground unless you have some kind of wood structure above. In any case bond these electrodes together UNDERGROUND.

[df0rster]

First ask your AHJ for guidance. Lacking guidance from AHJ then most installers would bond the grounding electrodes (ie rods) at the array with the grounding electrodes at the service. Here's why.......in the event of a high voltage event (ie lightning) then you do not want a large voltage differential between the electronics at the array and the electronics in your house. Without the GEC bonding the rods the high voltage may find an easier path through your power conductors between structures than going through ground.....in fact that event (ie step voltage) is certain since there is large resistance through the ground.

We don't have any AHJ in our small county. I'm not sure who I'd ask other than just following NEC.

In order to bond the electrodes I would have to run the proper grounding conductor (I think 6 awg minimum) from my array's grounding electrode into my subpanel at the house? Is it best to go ahead and have the grounding electrode at the array? It is about 180' away from my main panel and grounding rod.

Thanks!

[DanS26]

Ok. Next question then, can I just use a separate grounding rod at the array rather than bonding the GEC from array to service? That would be cheaper.

First ask your AHJ for guidance. Lacking guidance from AHJ then most installers would bond the grounding electrodes (ie rods) at the array with the grounding electrodes at the service. Here's why.......in the event of a high voltage event (ie lightning) then you do not want a large voltage differential between the electronics at the array and the electronics in your house. Without the GEC bonding the rods the high voltage may find an easier path through your power conductors between structures than going through ground.....in fact that event (ie step voltage) is certain since there is large resistance through the ground.

[df0rster]

If you are bonding the GEC from the array to the Service then refer to 250.166 (B) which requires that the GEC be not smaller than the neutral conductor. Most installers just lay a bare #6 in the trench with the conductors.

For the EGC then 690.45 and 690.46 will apply. Then based on your load the #10 EGC may be adequate.

Ok. Next question then, can I just use a separate grounding rod at the array rather than bonding the GEC from array to service? That would be cheaper.

[DanS26]

Good catch.

Actually using the solardesigntool.com site (which is 2014 NEC I think), it is specifying a 12awg ECG on the DC runs to the inverter. Which is what I am planning to use the 6/2 UF on. It is using 2 strings of 10-325W panels @ 180' distance.

Does that sound right? I'm sure its possible I have done something wrong though..

If you are bonding the GEC from the array to the Service then refer to 250.166 (B) which requires that the GEC be not smaller than the neutral conductor. Most installers just lay a bare #6 in the trench with the conductors.

For the EGC then 690.45 and 690.46 will apply. Then based on your load the #10 EGC may be adequate.

[SunEagle]

Yes. I'm an electrical engineer and found my copy of the 2017 NEC to be an invaluable aid, not just in meeting the code but also for some very useful guidelines.

For a few dollars more you can get the illustrated version of the NEC. It is a bigger format then the handbook but provides descriptions and pictures of what is being discussed. There is also an electronic format that can be downloaded to a PC, notebook or shared from a Server.

[BackwoodsEE]

Ok, that's the answer I was after.

Is it worth it for me to buy a copy of the NEC book? Or is there a simpler reference book that lays out the applicable codes I'll need to follow for a DIY solar install?

Yes. I'm an electrical engineer and found my copy of the 2017 NEC to be an invaluable aid, not just in meeting the code but also for some very useful guidelines.

[df0rster]

This may not apply to you......but 6/2 UF has a #10 ground wire.....thus it may not be adequate in your application. Check the code again but I think you need a #6 ground wire.

Good catch.

Actually using the solardesigntool.com site (which is 2014 NEC I think), it is specifying a 12awg ECG on the DC runs to the inverter. Which is what I am planning to use the 6/2 UF on. It is using 2 strings of 10-325W panels @ 180' distance.

Does that sound right? I'm sure its possible I have done something wrong though..

[DanS26]

In this case, the UF is much cheaper. I found a good deal on a 500' roll for about $.70/ft for 6/2. buying the thwn was not even an option at Lowes. Not a lot of choices around here for electrical supplies.

This may not apply to you......but 6/2 UF has a #10 ground wire.....thus it may not be adequate in your application. Check the code again but I think you need a #6 ground wire.

[SunEagle]

Interesting. My main service (200 amp)wire is 4/0 200' and the PoCo said this is as long as they will allow (it is aluminum). It is direct buried w/o conduit at 24"+. It hasn't shorted yet, but it isn't sitting in water constantly. I wish I had put it in conduit. From what I have seen it is very hard to unroll and install 200+' of wire without nicking something at least a little bit, even if its not all the way through it still creates a weak spot.

My house power feed is also a 200 Amp rated AL Direct Burial cable from the pole that runs about 180 feet to my meter. Since I am at an elevation of about 170 feet and the soil is very sandy I doubt I will every have an issue with water permeating the cable insulation.

I feel bad for those that live in a high water table area like organic farmer. It almost makes sense to go over head instead of U/G for any power runs.