PV Frame grounding versus Structure Grounding

lazza

HI All

It's been a crazy amount of time since I last posted anything, which is a real shame... basically I've been so busy I havent been able to dedicate any time to looking at forums and studying.

Anyway. I have a question on which I'd like to draw from your collective experiences.

We have installed in UK, Spain , Portugal and norms and regulations differ signfiicantly. Basically we have always considered array frame grounding essential, when it consists of an extraneous conductive part. We have never however bonded the PV panel frames themselves between each other, although I have seen that done on older installations. It was my undersanding that there is sufficient insulation in solar PV module design, along with the residual current (earth leakage) monitoring provided by the inverters, to exclude the need to bond PV panel frames together.

My question is:

Under what circumstances would it be necessary to interconnect/bond the PV panel frames together with earth conductors... in addition to the array structure? 

Thanks for any insights

Cheers
Lazza

BB.

Welcome back Lazza. Glad to hear you have not fallen off the planet.

Technically, most solar panel frames are bonded together "incidentally" by the metal racking. The only time they are not, is if using wood and/or plastic/rubber insulation between rack and metal framework.

Actually connecting a copper ground wire (and UL/NRTL recognized frame to wire clamp) is because most electric codes do not allow "incidental" grounding (mounting hardware to other grounded objects). They require separate grounding connection(s) of ground wire to frame... The idea being that anyone working on the system needs to physically remove the safety ground connection so they will not be shocked by disconnecting "incidental" grounds (via mounting hardware, etc.).

So, that is the reasoning behind ground wire to frame connections, vs just mounting to a metal structure, and grounding the structure.

Then there why ground frames/structures at all... Lightning strikes, static charge buildup on insulated structrue, and if there is a short from power (DC or AC) to ground--You want to structure grounded both to earth (typically for lightning and static charge), and back to the main panel/electrical ground to earth bonding--such as Neutral to Earth Bonding--So that if somebody walks up to the framework and grabs ahold, and they are standing in wet grass (as an example), they will not be electrocuted. The Green wire ground running back to the battery shack/main panel bonding is to provide a "good enough" current path to pop any circuit breakers/shunt any current back to the source to prevent the frame from becoming "Hot". While RCD breakers on AC work fine (they can be an option when green wire safety grounds are not present), on the DC power side, the RCD equivalent for DC systems is a bit less "safe". Many use a 1 amp fuse to trip the RCD/Ground fault for DC side, but even then, they may not really "safe" in all cases (like you have a 100 Volt solar array, and positive wire energizes frame--Most DC Ground Fault systems will not "make safe" such a fault...

A complex subject--Is there a specific configuration/issue you are trying to address? DC faults on solar power systems are a general weakness (shock, fire) and the only "safer" method to isolate fault conditions is the Micro Inverter type (one inverter per panel)--But that is not a common off grid configuration.

-Bill

lazza

HI Bill, thanks for your reply- good to hear from  you again. So in short, you'd recommend it then?

As for context: It's a Portuguese electrician that said that he wished to interconnect all the PV panels as well as the frame- in the UK, for example, this is unecessary, as far as I am aware. In Spain, there is also no specific requirement...

BB.

If you have legal responsibility, then running a #6 awg or equivalent to each frame, then to ground rod, and run to main system safety ground (and that means a single run of 6awg wire (or thermal permanent bonded splices).

That is the usual code for grounding.

If you have metal rails and framework that the panels are clamped to, and the frame is Earth and safety grounded (6awg for local ground rod and to electrical ground+equipment room grounding--ground rods for lighting, connecting grave to common electrical ground and ground rod is for short circuit) it is safe for day to day operations, but may not meet (many) code grounding requirements.

I suggest 6 awg minimum because smaller gauge wire has been shown to fuse (burn open) in some strikes. 6 awg or heavier does not (usually). Also 6 awg can be used for grounding up to 200 amp circuits (as save ground). 6awg typically fuses at 600 amps (roughly).

I have not looked at an electrical code book in decades, so the above is from memory. And I cannot tell you what to do.

I think copper grounding each solar panel frame is excessive if installed on metal rails that are electrically tied together, and if not required by your code, I would not lose sleep over it.

However you are hiring the local electrician, and if the extra cost is not an issue, I would not argue with him (belt and suspenders solution).

If you have lightning issues, we probably need to talk more.

PS: sorry for any typos, posted from phone.

BB.

I should clarify, do not tie any local grounding to any solar panel negative terminals. The array plus and minus leads should be floating all the way to the charge controller/gt inverter inputs.

Bill

lazza

Hi Bill

Thanks for all the info. And yes, that makes sense on all points.

The installation in question is with metal rails on a steel carport structure. In my opinion, bonding the aluminium structure to the steel frame then the steel frame to ground rods would be sufficient.

The problem is that he wants to interconnect copper grounding each PV panel frame aswell which will spoil aesthetics and create a day or two of extra work/costs. So unless explicitly required by Portuguese electrical code I'll try to avoid it. Does that sound sensible?

mike95490

dissimilar metals = corrosion

Aluminum racks & steel roof ??

Dave Angelini

In my experience the existing solar panel wires are what determine the required minimum wire gage to ground the panels and structure.
 So if the panels have #10 (+ & -) then that is what and AHJ will want to see.

 Yes everything needs to be grounded. Do what he wants unless you can make a compelling case to him. I usually just do whatever they want and fix it later if it is wrong, to me.

BB.

I think Lazza is referring to Aluminum Panel Frames and steel roof/frame for carport.

Yeah, aluminum is always tough to make good electrical connections too. Especially if wet conditions (on coast with wet fogs, etc.).

That is why most codes (that require grounding) have to use approved grounding lugs (correct metal to metal, pressure contact):

https://www.solar-electric.com/search/?q=grounding+lug

Operationally, grounding the frames won't matter. Looking at safety where you assume that any single point of failure "fails" safely.

-Bill

clockmanfran

Grounding of arrays and their mounted PV panels is always controversial in just the Countries in Europe never mind the rest of the World.

I have had some entertaining evenings with a few bottles of decent beer and wine with some knowledgeable European electrical engineers, and Earthing is always a subject we normally all try to stay away from.  
  However, recently the consensus seems to be going backwards.  Firstly Neutral bonding, very much a UK thing, is seen as problematic when other Energy creation devices try to be integrated into one system.

Any way by the end of the evening, :-     Earthing, PV array and mounted PV Panels …..   Put a solid Copper 3/4inch 1.5 meter long Earth rod into the ground with a minimum 16mm/2 earth cable connected and bonded to the metal frame of the PV array/frame, bonding cable from frame/Rail to frame rail should be no less than 10mm/2 thick.   

This earthing system was to be used with Double pole MCB's AND NOT common neutral bus bar and just the Live MCB like the UK use. 

I have over 14off earth rods at my various individual buildings connected to roof arrays, static arrays or PV trackers and also to each consumer distribution box with each having a double pole RCD as well as double pole MCB's for appropriate circuits.

My OzInverters also have RCD and Earth rod protection, as the OzInverter can AC couple and back charge to the Dc 48v batteries.

I am in France and this particular part of Normandy is very CLAY ground so good earth continuity is not a problem.  My consumer distribution boxes all confirm to the French Regs with RCD and double pole MCB's. But the French Sparky's tend to think that i overdo the Earthing.

Although I have mentioned a method that suits me and the local regulations, IT IS ABSOLUTELY NECESSARY to stick with your countries regulations where you can, and where you have things differing from the norms, then SAY SO with small labels so the next sparky can understand what's going on.

lazza

Ok thanks for all your inputs. Gounding does seem to be a contentious topic and alot of regs differ it seems. I'll make sure we adhere to Portuguese regs, but apply common sense to avoid unecessary connections.

We're in lock-down here which is fun. No more installations for a while, so I've got time to think about it!

Cheers
Lazza