Additional ground rods at garage sub panel

[Scot h]

Inspector called us on another ground rod or two at garage sub panel, wouldnt this additional grounding create a ground loop? Seems dangerous in my opinion.
My thinking is only one point of ground, at building main. Any responders?

 

[charlie b]

Separate structures require their own grounding electrode system. The inspector is right. Reference 250.32(A). Why are you concerned about a ground loop? Many buildings have ground loops surrounding them. It just makes for a better connection to planet Earth.

 

[augie47]

disregard

 

[Little Bill]

disregard

You speaking French again?

 

[infinity]

Inspector called us on another ground rod or two at garage sub panel, wouldnt this additional grounding create a ground loop? Seems dangerous in my opinion.
My thinking is only one point of ground, at building main. Any responders?

As Charlie stated you need a GES at a separate structure. You'll need two ground rods or prove that a single rod is 25Ω or less. What do you mean by a ground loop?

 

[roger]

My thinking is only one point of ground, at building main. Any responders?

At the detached building you will only connect the GES to the EGC, you will not bond it to the neutral so you will not have a loop for neutral current.

Roger

 

[tom baker]

I hear ground loop a lot, its almost an urban myth, the EGC does not normally carry current, so can't have a ground loop. And 250.2, 250.3 requires all electrial equipment and conductive materials to be bonded together ( isn't this a ground loop?)

 

[LarryFine]

And the earth is not considered to be a conductor in this sense, too.

 

[McLintock]

Seems dangerous in my opinion.

How Dangerous? Is the sub-panel bonded? Then it might be if the grounding side is energized. But if the sub-panel is installed correctly you can put as many ground rods as you can pound in


“ shoot low boys their riding shetland ponies”

 

[paulengr]

I hear ground loop a lot, its almost an urban myth, the EGC does not normally carry current, so can't have a ground loop. And 250.2, 250.3 requires all electrial equipment and conductive materials to be bonded together ( isn't this a ground loop?)

It’s not urban myth, it’s misapplication.

With communication systems with high frequencies, ground one end only. Grounding both ends creates a loop antenna that actually induces noise into the communication conductors. So ground one end only and avoid ground loops in open areas. Within an enclosure it’s a Faraday cage though so sometimes more connections are needed. As you get down to smaller physical dimensions though (cables) the rules of transmission lines and waveguides takes over.

Going the other way with power conductors at short distances you can ground either way. At long distances such as building to building though the issue becomes that ground resistance gets poor due to simple resistance from length. At that point the more connections you have the better. Ground loops are a problem only when you bypass your protection. So if you have a high resistance ground or GFCIs ground loops can destroy the protection design. This even gets to the point where the lightning codes mandate at least TWO paths to ground.

The other issue is when you have multipoint grounding you can create “stray voltage” or really stray voltage. This is a big problem on dairy farms because cows are affected by very low stray currents. The cause though is usually because the normal grounding is corroded and not functioning so it shifts to the secondary grounds.