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Radian in outbuilding--need separate ground rod?

Posted: Thu Nov 02, 2017 5:22 am
by Megunticook
I'm in the process of installing a Radian 8048 in an outbuilding close to the house. The existing main AC service entrance and panel are located in the house, and I'm installing a "critical loads" panel in the house as well. A set of underground conduit runs 40 feet from house to outbuilding.

Can everything share the existing grounding rod originally installed at our AC panel? Or does there need to be a separate rod at the outbuilding?

Re: Radian in outbuilding--need separate ground rod?

Posted: Thu Nov 02, 2017 7:16 am
by Kent Osterberg
It depends on the local codes where you are at, but in most locations a second grounding system at the outbuilding is required by NEC250.32(A).

Re: Radian in outbuilding--need separate ground rod?

Posted: Thu Nov 02, 2017 8:51 am
by Megunticook
Thanks. So I ground the Radian's load center equipment ground bus to a steel electrode driven into the ground?

I thought I read in the Outback materials somewhere that the load center should be connected to the main ground at the existing service entrance and there should not be multiple grounds in the system.

Re: Radian in outbuilding--need separate ground rod?

Posted: Thu Nov 02, 2017 9:11 am
by Kent Osterberg
You probably need two 8' x 5/8" ground rods that are six feet apart.
The ground terminal in the Radian load center should be connected to the grounding electrodes at the out building.
There should be four wires going to the electrical panel at the house: L1, L2, N, and Gnd.
The neutral wire should be connected to ground at only one location. For a grid backup system, the neutral ground connection should be left at the main panel. For an off-grid system, it is probably best if neutral it is connected to ground in the Radian load center and not at the house; but it can be done the other way.

Re: Radian in outbuilding--need separate ground rod?

Posted: Tue Jul 02, 2019 1:18 pm
by SwDoctor
I am off grid, so no code to adhere to in my installation.
Metal structure was engineered with the very center being the common ground, minimizing carrying an emp to anything potentially damaging.

Lets use an example:
ONE common ground is superior in combating lightning damage.
Consider that you have two grounding points, lets say on each end of a 1mile long driveway.
Then lightning strikes at or near one of the rods.
The rod will be energized at the potential of the ground rod near the strike, but the other ground location will not be energized at the same fashion/time, causing current to flow along ground1 to ground2. (killing the ground wires and circuits inbetween - not to mention adverse readings on sensors and data lines)

With one ground, the remote location would have never been energized, but a wiring fault would have been taken to the proper earth path. (without having to decide which path is proper)
.
Code is king if code dictates...
- but ONE ground is the best option for minimizing damage to systems.