Ground rod question

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Stevenfyeager

Senior Member
Location
United States, Indiana
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electrical contractor
Usually I drive a ground rod when I find an old sub panel fed by 3 wires from a different building. ( from a house panel. What if there are two suboanls in sequence? First one comes underground to a private utility pole panel. Then overhead to a building panel. All existing 3 wires between each. Should I drive a ground rod at both panels? Thank you
 
Stevenfyeager said:
Usually I drive a ground rod when I find an old sub panel fed by 3 wires from a different building. ( from a house panel. What if there are two suboanls in sequence? First one comes underground to a private utility pole panel. Then overhead to a building panel. All existing 3 wires between each. Should I drive a ground rod at both panels? Thank you
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Just at the first one, and truthfully a single rod is likely not enough to comply with code.

Also even new panels with an EGC in a separate building require a grounding electrode system.
 
iwire said:
Just at the first one, and truthfully a single rod is likely not enough to comply with code.

Also even new panels with an EGC in a separate building require a grounding electrode system.
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When using a ground rod it must be supplemented by one of the ways listed in 250.53(A)(2)
 
ActionDave said:
Two ground rods. Cowboy gave the code reference.
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Thank you. I can put two ground rods 6 feet apart. But if I do that at the first subpanel, it still seems a little inadequate to me for the second sub panel which is in the out building that only has 3 wires feeding it. I'm used to driving ground rods for existing subpanels in detached garages when I discover someone had run only 3 wires to it. Should I drive rods for both subpanels?
 
bullheimer said:
so what, you just drive ground rods for fun?
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You don't? I love playing with the rotary hammer. :p

But, let's be honest, the only down side of too much grounding is the addition cost and time spent. If you're using a rotary hammer driving a ground rod takes 30 seconds... if you're using a sledge hammer you may want to reconsider, especially if you are in Florida where our "soil" is all coral.

If you are within the requirements of the NEC but, in YOUR opinion it is not safe enough, there is your answer.
 
Stevenfyeager said:
I'm sorry, I'm a little confused. If I drive ground rods for one 3 wire sub panel, shouldn't I drive ground rods for the other 3 wire subpanel? Or do two panels being in sequence make a difference? Thank you.
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Think of it this way, you are not driving rods for sub panels, you are driving ground rods for separate buildings or structures.

In other words the ground rods or other electrodes at the main service are for the building it is in or on. In that building you can add as many sub panels as you please without adding more grounding electrodes.

However run a feeder from that building to a separate building or structure and you will need to add electrodes at that building. Once those electrodes are installed at that separate building you could add as many sub panels in that building as you want without adding any more electrodes.
 
Stevenfyeager said:
Thank you. I can put two ground rods 6 feet apart. But if I do that at the first subpanel, it still seems a little inadequate to me for the second sub panel which is in the out building that only has 3 wires feeding it. I'm used to driving ground rods for existing subpanels in detached garages when I discover someone had run only 3 wires to it. Should I drive rods for both subpanels?
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I'm getting the impression that you are wanting to substitute the lack of an Equipment Grounding Conductor for a Grounding Electrode Conductor (System). Each has a different function. ;)
 
jordan0316 said:
You don't? I love playing with the rotary hammer. :p

But, let's be honest, the only down side of too much grounding is the addition cost and time spent.
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Not true. "Too much grounding" can be dangerous.

jordan0316 said:
If you are within the requirements of the NEC but, in YOUR opinion it is not safe enough, there is your answer.
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More grounding never makes anything any safer.
 
Fitzdrew516 said:
More grounding never makes anything any safer.
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True, the rod GE and earth grounding almost never facilitates a breaker opening when there is a fault- fault current returning to it's source via bonded metal parts and the egc, which is connected to the grounded conductor, (svc neutral) does.
 
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jordan0316 said:
You don't? I love playing with the rotary hammer. :p

But, let's be honest, the only down side of too much grounding is the addition cost and time spent. ...
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I dislike this attitude. As Fitz said, too much grounding, or improper grounding, can be dangerous, especially in regards to lightning side flash. The frequency with which we're forced to spend additional cost and time to create potentially dangerous situations irks me.
 
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