PV Module Frame conductivity

[LATTC Student]

During the grounding system installation for my JA Solar Array, I discovered something strange and I am hoping this group has an simple explanation. I tied the rails and the panels to my grounding system. When I test continuity of the rail system, great - tests fine, all the way thru the ground rod (0.1Ω). The panel frames however show OL on my DMM's, even when I touch two spots on the module frame with my leads just an inch away from each other. I thought these frames were Aluminum and conductive (polished, powder coated, whatever). I just get an OL (and no continuity) when I test them for ground purposes. Is it just my lack of understanding or am i not making a good connection with the leads?

 

[ggunn]

During the grounding system installation for my JA Solar Array, I discovered something strange and I am hoping this group has an simple explanation. I tied the rails and the panels to my grounding system. When I test continuity of the rail system, great - tests fine, all the way thru the ground rod (0.1Ω). The panel frames however show OL on my DMM's, even when I touch two spots on the module frame with my leads just an inch away from each other. I thought these frames were Aluminum and conductive (polished, powder coated, whatever). I just get an OL (and no continuity) when I test them for ground purposes. Is it just my lack of understanding or am i not making a good connection with the leads?

This is normal. In air, aluminum rapidly acquires a very thin coating of non conductive aluminum oxide; that's why everything that attaches to the frames that needs a conductive path has to have teeth or knife edges to penetrate the oxide to make contact with the metallic aluminum under it.

 

[LATTC Student]

This is normal. In air, aluminum rapidly acquires a very thin coating of non conductive aluminum oxide; that's why everything that attaches to the frames that needs a conductive path has to have teeth or knife edges to penetrate the oxide to make contact with the metallic aluminum under it.

I guess I will need to do some research online for proper grounding on the modules themselves. I tied the grounding system to the rails and had assumed the PV frames touching the rails were therefor grounded. I am using Ilsco GBL-4 alay-in lugs now. Will replace them. So I will need to come up with a way to penetrate the oxidized surface of each of the 19 PV modules frames that I have to establish a good ground to each for safety.

Thanks GGunn!

 

[electrofelon]

I guess I will need to do some research online for proper grounding on the modules themselves. I tied the grounding system to the rails and had assumed the PV frames touching the rails were therefor grounded. I am using Ilsco GBL-4 alay-in lugs now. Will replace them. So I will need to come up with a way to penetrate the oxidized surface of each of the 19 PV modules frames that I have to establish a good ground to each for safety.

Thanks GGunn!

in the earlier days of PV the WEEB clip was invented to provide reliable continuity between things like frames and rails. Most systems now have this engineered into the hardware. A friend and I have a "homebrew" racking system we install and we still use WEEBS between the panel and the rails.

 

[jaggedben]

UL 2703 is a standard for solar mounting systems including providing electrical bonding. If you have a racking system such as Ironridge or Unirac that is listed to 2703, just follow the instructions to bond the modules.

In addition to what ggunn said about natural oxidation, panel frames are also factory anodized. One trick I found sometimes works is to stick your meter probe on the inside edge of the mounting holes on the bottom of the frame edges, to test continuity. These holes are sometimes drilled after the anodizing and therefore make decent contact, if they haven't been in the elements too long.

 

[ggunn]

UL 2703 is a standard for solar mounting systems including providing electrical bonding. If you have a racking system such as Ironridge or Unirac that is listed to 2703, just follow the instructions to bond the modules.

In addition to what ggunn said about natural oxidation, panel frames are also factory anodized. One trick I found sometimes works is to stick your meter probe on the inside edge of the mounting holes on the bottom of the frame edges, to test continuity. These holes are sometimes drilled after the anodizing and therefore make decent contact, if they haven't been in the elements too long.

Yeah, anodizing is an electrochemical acceleration of the oxidizing process. Most (all?) module racking clips these days have sharp features where they make contact with the module frames that pierce the oxide to make electrical contact with the elemental aluminum underneath. Depending on his racking hardware the OP may already have what he needs.

 

[LATTC Student]

UL 2703 is a standard for solar mounting systems including providing electrical bonding. If you have a racking system such as Ironridge or Unirac that is listed to 2703, just follow the instructions to bond the modules.

In addition to what ggunn said about natural oxidation, panel frames are also factory anodized. One trick I found sometimes works is to stick your meter probe on the inside edge of the mounting holes on the bottom of the frame edges, to test continuity. These holes are sometimes drilled after the anodizing and therefore make decent contact, if they haven't been in the elements too long.

Most interesting. So I retested a module that had a "nick" on the outer frame. When I tested continuity from the rack as well as a test from the GBL-4 grounding terminal to this nick, or exposed point in the frame, I got continuity. So that's a relief.

I am guessing oxidation/anodized layer of the frame itself isn't resistive enough to prevent lightening to flow thru it to the ground tied to the module frame then?

 

[LATTC Student]

I retested all the panels from the factory drilled holes on the bottom of the frames to ground rod. As an added safety measure, I ended up grabbing a bunch of 5/8 locking washers from the hardware store today and installed them under my existing midspan washers. Retested continuity across all 19 modules from one of the abovementioned drilled holes in each frames to the ground rod, bingo. . . . fully meshed grounded system ~0.01Ω.

Thanks to all for the wisdom and guidance. Still learning from your experience daily! I can thankfully say that I am done with the grounding system.

 

[GoldDigger]

I suspect that the oxide layer would not hold up to a Megger either, although aluminum oxide is known to form a high resistance at line voltages at carelessly made junctions. You need to prevent oxide formation in the junction either with Noalox or a gas tight metal to metal junction.

Sent from my Pixel 4a using Tapatalk

 

[jaggedben]

I am guessing oxidation/anodized layer of the frame itself isn't resistive enough to prevent lightening to flow thru it to the ground tied to the module frame then?

Most certainly lightning would blast right through that. Also grounding the array to a ground rod is pretty much useless to protect against lightning as far as I know. There's a lot of confusion about this and some of that confusion even made it into a code requirement for a while. But that's out again now.

 

[electrofelon]

Since we are on the topic of bonding, corrosion, and interconnection of PV components, one thing I have always been puzzled by is the industries extensive use of stainless steel hardware where in contact with aluminum. Stainless to aluminum is a horrible combination on the galvanic series. Just the other day I had to disassemble some stainless bolts holding aluminum together. It had been in service for 7 years and the aluminum at the mating services was severely corroded. The assembly was on the cusp of being non removable. The galvanic action, along with high cost, low strength, and the galling issue make stainless a puzzling choice for most PV components. Strange how WEEBS are stainless, I wonder how long those things will work?

 

[jaggedben]

Maybe because the stainless basically doesn't corrode? Seems to me that whenever I'm servicing something the stainless parts are still very intact and easy to undo, galling aside, and the corrosive build up on the surrounding aluminum is not structurally or electrically consequential. Whereas galvanized steel is often starting to simply rust and I can't the stuff apart, and I wouldn't trust it for structural or bonding. Is there a better choice? That's economical?

 

[electrofelon]

Maybe because the stainless basically doesn't corrode? Seems to me that whenever I'm servicing something the stainless parts are still very intact and easy to undo, galling aside, and the corrosive build up on the surrounding aluminum is not structurally or electrically consequential. Whereas galvanized steel is often starting to simply rust and I can't the stuff apart, and I wouldn't trust it for structural or bonding. Is there a better choice? That's economical?

I think hot dipped galvanized steel is a much better choice where in contact with aluminum. I typically see horrible consequences when stainless is used on aluminum, they are galvanically very far apart.

 

[pv_n00b]

I think hot dipped galvanized steel is a much better choice where in contact with aluminum. I typically see horrible consequences when stainless is used on aluminum, they are galvanically very far apart.

Zinc is lower on the galvanic scale than aluminum so the thin zinc coating will corrode away then the steel will rust. The galvanic corrosion in an above ground PV installation will depend a lot on the availability of electrolyte in the process. So within 10 miles of the sea, float-o-voltaics, and around wastewater treatment plants are a high corrosion environment and extra precautions should be taken.

 

[electrofelon]

Zinc is lower on the galvanic scale than aluminum so the thin zinc coating will corrode away then the steel will rust.

Ok good point. I guess it comes down to an analysis of what you want to corrode the fastener or the surrounding structure? In my experience, the aluminum/stainless reaction is very nasty and the fastener gets very difficult if not impossible to remove in a short period of time. If future fastener removal is not a concern then perhaps that is a good combination......however I don't think it's a given that we only care about the fastener and not the integrity of the surrounding material.

 

[pv_n00b]

Ok good point. I guess it comes down to an analysis of what you want to corrode the fastener or the surrounding structure? In my experience, the aluminum/stainless reaction is very nasty and the fastener gets very difficult if not impossible to remove in a short period of time. If future fastener removal is not a concern then perhaps that is a good combination......however I don't think it's a given that we only care about the fastener and not the integrity of the surrounding material.

I agree it can get difficult, a lot of aluminum and stainless interaction on boats that I have had to deal with over the years. But that is in a high corrosion environment. In a low corrosion environment, I've seen aluminum and stainless hardware get along for decades with little galvanic corrosion. The natural anodizing coating on aluminum does a pretty good job isolating it from the stainless under low corrosion conditions.
Unfortunately, a lot of people installing PV systems are not doing the job with it in mind that someone has to take all this apart at some point in the future, preferably non destructivly.