Main vs. sub panel for dedicated lines

For a sub panel in an out building, separate building, a ground rod (Grounding Electrode) is required. The ground rod is connected to the equipment ground bar in the sub panel creating a grounding electrode system for the separate building.

For a sub panel located in the same building as the main electrical service panel the separate earth connection ground is not required. If not required why would anyone want it? The separate earth connection can/does cause more harm than good. In fact the separate earth connection can/will add noise to the branch circuit equipment grounding conductors connected to the earth connected ground rod.

This guy has helped over the years in writing parts of the National Electrical Code, (NEC).
Auxiliary Grounding Electrode. (NEC 250.54)
https://www.youtube.com/watch?v=gg4wBI7bWgI
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Thanks! I am currently away from home and will return by end of the month. I will have my electrician help me install the sub panel. I will use it for my audio system. I will get back to everyone once this has been accomplished. 

@jea48
Hi Jim, the service I mentioned is the one where you kindly offered advice. Installation was from the drop to a new meter, then inside to a Square D 100A panel, 60A subpanel.

This is a small Philly rowhome where outside the house is pavement. Now don’t freak out, this might be  Philadelphia code; both grounding rods are drilled into the basement cement floor near the rear wall. They’re 3’ apart, sunk into mother earth. I can only see one rod which is wired to the main panel. The 2nd rod is obscured behind my washer/dryer. I will look for the wire.

Question: why are two ground rods used?

I’m guessing the second rod isn’t wired to the subpanel because the main panel is ground, correct?

What difference does it make? The sub panel is still receiving power from the main panel. Just go to main panel and fit a new 20 amp breaker, or if no room a piggy back breaker. Then use 20 amp 12 gage romex, the yellow jacketed romex. If you like making more work for yourself, then use 10 gage romex...to me, no benefit and way to stiff, over kill....then install a stand alone receptacle contained in a handy box. I’d recommend the audioquest nrg Edison receptacle and cover plate, excellent quality. This is an easy diy project. If the main panel is of 200 amp service, I’m having a hard time seeing the need to add a sub panel. You are in no way going to tax the main panel by running audio equipment.

lowrider574,353 posts   

06-03-2021  
 3:04pm


Question: why are two ground rods used?

Hi @lowrider57

From one of my above posts:
06-02-2021
8:24am

Minimum required number of driven ground rods for the main service panel technically is one, * IF *, the ground rod to soil resistance is 25 ohms or less.
How can the electrician know for sure if it is 25 ohms or less? With testing equipment that is made to test it. If an electrical inspector sees only one ground he will ask to see a print out of the test. It is cheaper by far for the electrician to just drive two ground rods and be done with it.

I am curious what’s going on with the two ground rods in the basement. Sure would like to know. 3 ft apart? Not 6 ft apart? Are the two rods connected together by a bare #6 solid copper wire?

How about the old ground rod that was used for the old service? Did the electrician use it for the new main electrical service as one rod and the new rod(s) in the basement for the other? Curiosity killed the Cat.....

Best regards
Jim.