diy solar

diy solar

Grounding Electrode Recommendations

colinf

New Member
Joined
Jul 18, 2022
Messages
11
I have a fully offgrid system powered primarily by a Growatt SPF-DVM 4000T. The system powers a large site with multiple cabins on the AC side. The inverter unit is located directly next to the panels with a buried grounding electrode. All solar panels and equipment housings are bonded and there is a Clamper 40kA 150V SPD on the DC side of the inverter.

There are multiple cabins connected to the inverter in a daisy chain configuration, the furthest being just over 100m away. I have a friend in the area who recently had his Growatt inverter destroyed by a lightning strike which struck a cabin (we live in the tropics and rainy season can mean a lot of heavy electrical storms) on his AC side, so I am figuring out the best way to put a SPD on the AC side. Is it best to have all the cabins EGC run the whole distance back to the inverter and to a DPS in the main AC panel? Or would a better design be to put a second grounding electrode at the furthest cabin? If that is the case then the SPD is still likely best placed directly next to the inverter? In the event of a lightning strike would a voltage build up between the two electrodes and damage devices in the cabins?

Thanks
 
If the two rods are not bonded to each other, yes.

Understood, but then what benefit does having a separate grounding electrode at the far side of the site hold, if it is bonded directly back to the earth busbar in the main AC panel?
 
Understood, but then what benefit does having a separate grounding electrode at the far side of the site hold, if it is bonded directly back to the earth busbar in the main AC panel?


Did you watch the video? There is absolutely, positively no benefit whatsoever. In fact it substantially increases the potential for damage. When lightning strikes, there is a huge voltage gradient.

If one rod is closer, and there is ANY kind of connection between the rod and the other, it will take that path.

A second ground rod is still connected to the first through the ground wire that should connect all the way back to the inverter. Thus, you are inviting the lightning into the wiring of your dwellings and equipment to get to the other ground rod MUCH faster than it would via earth.

You really need to watch the video. Grounding/Bonding is where most mistakes happen.

Simply put:

Everything in a system above the ground should be connected together.
Everything in a system below the ground should be connected together.
There must only be ONE connection between what's above the ground and below the ground.

Additional (auxiliary) ground rods do not protect against lightning. Auxiliary ground rods NOT connected to the main ground rod/each other vastly increase the possibility of damage due to a lightning strike.
 
Last edited:
You really need to watch the video. Grounding/Bonding is where most mistakes happen.

Simply put:

Everything in a system above the ground should be connected together.
Everything in a system below the ground shoudl be connected together.
There must only be ONE connection between what's above the ground and below the ground.

Additional (auxiliary) ground rods do not protect against lightening. Auxiliary ground rods NOT connected to the main ground rod/each other vastly increase the possibility of damage due to a lightning strike.
Very helpful. Mike Holt is great but I hadn't see that. Thank you.

edit: to delete something potentially confusing to future readers.
 
Last edited:
Very helpful. Mike Holt is great but I hadn't see that. Thank you.

Did you meant "shouldn't" when you said "Everything in a system below the ground shoudl be connected together"?

No. Everything in a system below the ground SHOULD be connected together, i.e., if you have 2 ground rods, they should be connected. 250.50 requires all grounding electrodes to be bonded.

Here's what happens with lightning strike or utility fault and unbonded ground rods:



250.50 Grounding Electrode System

All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.
Exception: Concrete-encased electrodes of existing buildings or structures shall not be required to be part of the grounding electrode system where the steel reinforcing bars or rods are not accessible for use without disturbing the concrete.
 
Last edited:
Here's what happens with lightning strike or utility fault and unbonded ground rods:
Thanks; I haven't watched that in years. It does point out the importance of word choice and the dangers of simplifying things to explain them. There are so many subtleties to grounding and a lot of best practices have changed dramatically over the last 30 years... without much fanfare.

@conlinf ... your best bet is to just provide an SPD at each cabin and the inverter. It won't protect against everything but at least you are trying.
 
No. Everything in a system below the ground SHOULD be connected together, i.e., if you have 2 ground rods, they should be connected. 250.50 requires all grounding electrodes to be bonded.
That's what I thought. I cleaned up my post and I see you did your original to clean up the typo.
 
Back
Top