Solar Wire for my ground mount

[ElkPicture]

New bee here. I'll be running 150 feet of PV wire out to my very first ground array.

My Solar panels: https://signaturesolar.com/product_images/AdaniSolarASB-M10-144-535bifacial.pdf ( I'll have a bunch of these in series. up to around 400v)

My Question:
1) I'm a little confused on what wire size to choose. I figure I could get 15 amps coming through the wires. According to this chart I should be using 6 awg wire: https://www.bluesea.com/support/articles/Circuit_Protection/1437/Part_1:_Choosing_the_Correct_Wire_Size_for_a_DC_Circuit.
However, in this post(https://diysolarforum.com/threads/solar-pv-wire-sizing.83570/) everyone is mention to use 10 and 8 awg wire and his run is 300 feet. Am I missing something? I'm ok if I have some power during super ideal conditions... but I also don't want to melt my wires if there are some super perfect conditions with cloud edge effect. 6 awg will be very expensive. Would it be ok to go with 8 or 10 awg?

2) 100' of this will be underground... Do I need special under-groud wire to account for potential wet condition or should I just use THHN?

3) It looks like this could get pretty expensive with 2 strings of panels(4 wires total). Where do you guys find it best to purchase you wire for a project like this? Local supply store?

Thank you for you help. I love this forum.

-George

 

[blrmaker]

I believe everyone will tell you that you need 5 wires. Don't forget to run a ground wire as well.

 

[ricardocello]

Calculate your maximum current Isc for each string. If that is 15A, then 10 awg is sufficient for 100ft, even accounting for voltage drop.
But I would plan for the future, and run 8 AWG. You may get more panels and want them in parallel.

Running PV wire in conduit is painful and unnecessary, I would run THHN/THWN2 it is cheaper and easier.
However, you will need a junction box to transition to PV wire for outdoor use.

You must also run a ground wire (EGC) from the house to the ground array! 10 or 8 AWG as above.
Preferably THHN/THWN2 with green insulation.

 

[ElkPicture]

I believe everyone will tell you that you need 5 wires. Don't forget to run a ground wire as well.

Can't I just drive a ground rod in near my panels and ground all the panels and frame to that rod... saving me from running a long ground wire.... only to go in a ground rod near my house.

 

[ricardocello]

Where do you guys find it best to purchase you wire for a project like this? Local supply store?

It will be difficult to beat the big box stores on THHN in 250 ft spools, some local electrical supply stores can occasionally.
I also use wireandcableyourway.com for specific lengths, sometimes that is cheaper.

 

[ElkPicture]

Calculate your maximum current Isc for each string. If that is 15A, then 10 awg is sufficient for 100ft, even accounting for voltage drop.
But I would plan for the future, and run 8 AWG. You may get more panels and want them in parallel.

Running PV wire in conduit is painful and unnecessary, I would run THHN/THWN2 it is cheaper and easier.
However, you will need a junction box to transition to PV wire for outdoor use.

You must also run a ground wire (EGC) from the house to the ground array! 10 or 8 AWG as above.
Preferably THHN/THWN2 with green insulation.

isn't THHN only for dry conditions. I though I needed conduit... but that would easier.

 

[ricardocello]

Can't I just drive a ground rod in near my panels and ground all the panels and frame to that rod... saving me from running a long ground wire.... only to go in a ground rod near my house.

That will not protect you from potential AC currents coming back from the house when you touch the solar panel frames.

 

[ricardocello]

isn't THHN only for dry conditions. I though I needed conduit... but that would easier.

THHN/THWN2 is cross listed for wet environments. Make sure the THWN2 is explicitly called out.
It goes into conduits, not for direct burial.

 

[cs1234]

I would put any relatively thin, jacket having cable in conduit regardless, if in or on the ground. The critters, they like to chew!

 

[timselectric]

Can't I just drive a ground rod in near my panels and ground all the panels and frame to that rod... saving me from running a long ground wire.... only to go in a ground rod near my house.

That's earthing, not grounding.
You are not going to the ground rod at the house. You are connecting to the grounding system at your house. (Where the N/G bond is)

 

[ricardocello]

I though I needed conduit.

You do. PVC 3/4” or 1”, but most people here will tell you to use the biggest you can afford so you don’t have to dig twice when you decide to expand later. THHN/THWN2 always goes in conduits. UF-B can be buried directly, but roots and critters can cause issues.

I ran 220’ of 1 1/4” PVC and already regret not just doing 2” PVC.

 

[sumpower]

Can't I just drive a ground rod in near my panels and ground all the panels and frame to that rod... saving me from running a long ground wire.... only to go in a ground rod near my house.

If you are getting this inspected the Code required ground must be run with the PV array conductors and attached where the neutral/ground bond is, as stated by @timselectric above.

 

[ElkPicture]

That's earthing, not grounding.
You are not going to the ground rod at the house. You are connecting to the grounding system at your house. (Where the N/G bond is)

This post suggested that "The Lightning system has its own ground rods and is usually isolated from the equipment ground system." That makes sense to me. That makes sense to me as if lightning strikes my panels I want don't want to direct that power into my house. A couple mentioned that their inspectors also agreed with this.
^^ @sumpower

@ricardocello My panels will be in the middle of a field. not near any AC Power.

 

[cs1234]

This post suggested that "The Lightning system has its own ground rods and is usually isolated from the equipment ground system." That makes sense to me. That makes sense to me as if lightning strikes my panels I want don't want to direct that power into my house. A couple mentioned that their inspectors also agreed with this.
^^ @sumpower

@ricardocello My panels will be in the middle of a field. not near any AC Power.

They don't have to be near AC power to have AC power come back on the lines feeding the mppt from the panels. It really depends on what inverter you are using. Many of them that have MPPT's and inverters in the same box manage to dump AC back onto the solar lines, that then goes onto your panels and racking and won't dissipate if not fed back into your building ground system (the one the inverter is on). Putting a separate ground rod in the ground at the array does nothing for that, because the AC wants to go back to the source, which is the inverter dumping it onto the lines, not the panels.

I'm not an electrician like these other guys though, so take this with a grain of salt. It's just my understanding of the issue having read every thread on it.

 

[ricardocello]

@ElkPicture This topic is very frequently discussed on the forum. Do a search for Pv grounding, it will go on for many pages.
Here’s a sample from @timselectric.

Post in thread 'Proper Grounding.'
https://diysolarforum.com/threads/proper-grounding.80527/post-1048720

And one from @Hedges :
Post in thread 'Not grounding panels'
https://diysolarforum.com/threads/not-grounding-panels.76852/post-982379

And my favorite (put up a fence!)
Post in thread 'Multiple grounding rods for solar panel install and electrical devices?'
https://diysolarforum.com/threads/m...tall-and-electrical-devices.75118/post-954641

Thread 'I got a small electrical shock when grounding solar panels. Why?'
https://diysolarforum.com/threads/i...-shock-when-grounding-solar-panels-why.68518/

 

[ricardocello]

That makes sense to me as if lightning strikes my panels I want don't want to direct that power into my house.

Which is more likely: Someone touching the panels and getting zapped, or lightning hitting the panels and conducting it all the way back to your house? Direct lightning strikes cannot be mitigated, period. Safety grounding and lightning protection are two separate concepts, and they may work against each other.

But static buildup can be dealt with with beefy surge protectors like the midnite solar MNSPDs.

And don’t you think if the lightning is that determined that it will just follow the + and - conductors anyway?

 

[ElkPicture]

And one from @Hedges :
Post in thread 'Not grounding panels'
https://diysolarforum.com/threads/not-grounding-panels.76852/post-982379

Thanks, This is interesting. Will Prowse mentions here that you shouldn't ground your solar array when using a all in one unit(which is what I have... 6000xp). So his advise conflicts with what you guys are saying... unless I'm not understanding what he's saying. @ricardocello @timselectric

 

[timselectric]

This post suggested that "The Lightning system has its own ground rods and is usually isolated from the equipment ground system." That makes sense to me. That makes sense to me as if lightning strikes my panels I want don't want to direct that power into my house. A couple mentioned that their inspectors also agreed with this.
^^ @sumpower

@ricardocello My panels will be in the middle of a field. not near any AC Power.

Lightning protection is a separately installed system. It doesn't connect to what you want to protect. It is built above and around what you want to protect.
Electrical grounding is for personal safety. Everything you can touch must be kept safe to touch.
AC power can (or already does) exist on your PV wiring.
Either due to a fault, or by design.

 

[timselectric]

Thanks, This is interesting. Will Prowse mentions here that you shouldn't ground your solar array when using a all in one unit(which is what I have... 6000xp). So his advise conflicts with what you guys are saying... unless I'm not understanding what he's saying. @ricardocello @timselectric

You misunderstood what he said.
He was referring to grounding/bonding the negative PV conductor. Which you should not do.
You should only ground the frames.

 

[ElkPicture]

You misunderstood what he said.
He was referring to grounding/bonding the negative PV conductor. Which you should not do.
You should only ground the frames.

That makes sense. This is very helpful! I'll plan on running a ground wire.

Do you think #10 THWN wires would work for my 2 strings of panels? 5 wires total. They are the largest bi-facial panels I can find. (Up to 15 amps on each string...running 150 feet).

For my grounding wire I was going to use #6 bare copper from my panels into a junction box and then use #10 green THWN under ground over to the ground bar on my inverter, which connects to my house ground and GN bond. Does this sounds ok for my ground?

Thanks.