Another Ground Thread 😬

[CVCPJared]

Ok, I've read probably 40 grounding threads on here, watched some YouTube, read some articles, and have a plan. But my comprehension is pretty low, so I'm hoping to get advice from some of the experts whether or not I'm missing something

So exhibit A: rough layout.


So, those tiny little rectangles on the house and shed are main panel outside the house and "service panel" inside the battery shed that will feed the main panel. There's about 20ft between the house and shed.

The house has an Ufer ground (I beleive it's called), 20ft steel rod in the concrete or something like that. Exhibit B.


This is off-grid. AHJ says i need a seperate grounding rod for a seperate structure (shed). My intent is to make it West of the shed, between the shed and panels, tie both of those into it. Now from the little I comprehend, in a theoretical lightning strike, lightning hits some random spot near the array, and let's say 200,000 volts goes into the grounding rod, and that same strike maybe puts 100,000v into the Ufer ground further away. What I understand is that since those are connected through the equipment, and there's a 100,000v difference, it wants to shoot said electricity through your MPPT, Inverter, and panels, to the Ufer Ground. Is that correct or completely missed the boat?

So the theoretical solution for that is bare copper wire connecting the 2 earth grounds. AHJ is not requiring this. Is that correct and should I do that or am I way off base here? If that is done, does that mean SPD are not required/beneficial at that point, or is this a "throw the kitchen sink at it" situation where the ideal solution is try everything and hope something works?

Thanks for reading the book and for your time!

 

[Norwasian]

I'm not certain how you are considering connecting the ground bond wire. If I am not misunderstanding, I think the 100,000v surge that you speak of should not, theoretically, be passing through your equipment--at least, not before saturating both of your bonded ground rods. Connecting via a bare copper wire makes sense, though, unless you are planning to put it into conduit with other wires. @timselectric would probably be a good source to confirm these points.

The core principles of grounding are covered well in this video, which you may have already run across here if you have read dozens of threads on the topic.

The video includes the fact that the ground is not a very good conductor, which is precisely why there can be such a difference in voltage potential between two ground points. As I understand, that second ground is not helpful in many cases but if your AHJ requires it, then you would certainly want it bonded as you are planning to do.

I'm curious though, and maybe Tim would have an answer for this--what impact does oxidation of that bare copper wire have over time on its grounding ability? Would insulated wire be nearly equivalent after the passage of a few years, especially in humid climates?

Personally, I pity those who, in lightning-prone areas, are required to have earth grounds, as in my experience they expose the "grounded" electronic devices to increased risk of lightning damage. Contrary to popular mythology, lightning does not strike randomly, in a new place every time: there are reasons it hits where it does.

 

[Bongbong]

If you have more than one ground rod and there are other wires between the buildings, bond the ground rods together.

In addition I lean towards bonding all metal parts in the house, including the foundation etc and shed to the ground rods and instead of connecting neutral to ground, use a Residual-Current Circuit Breaker (or Ground Fault Circuit Interrupter) on every circuit. But do whatever the code requires, as there is no perfect system and you don't want to run foul of the local regulators or insurance companies.

 

[CVCPJared]

Yeah, was talking about a bare copper wire. I'm not in a super lightning-prone area, but I have open trenches right now, so if it's going to get done ever, I figure now is the time. Just wanted to make sure I'm not doing something stupid or unnecessary. Thank you for your answers, I appreciate it