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I recently found out that our sole ground rod is only 4 feet long. That said, I want to add a properly-sized ground rod to "improve" the grounding system and hopefully comply properly with the electrical code.

Our current electrical system is the one in blue, where M is the meter, B is the breaker. Both are grounded via #8 wires connected to the ground rod. The ground bus bar in the main panel is also connected to the ground rod via a #8 wire.

The existing ground rod is in front of the house. However, there isn't much space in front to place another rod there. That said, I'm planning on putting the additional rod at the back of the house. In effect, the two rods will be around 20 meters apart.

Now, the question is: Can I just run a #8 or #6 wire from the 8-ft ground rod back to the Main Panel and just bond it to the ground bus bar, in effect bonding the two ground rods? Or do I need to run a separate wire all the way from the 8-ft rod to the 4-ft rod? Note that the Main Panel will be closer to the 8-ft rod. They will be just 7-8 meters apart.

System diagram

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    Is there any chance of replacing the existing ground rod instead? In the event of a lightning strike nearby there could be a very high potential difference between two rods. Cows can be killed like that, and their legs are less than 2 meters apart. Advice for humans caught outdoors with lightning nearby includes keeping one's feet together. – Andrew Morton Mar 10 '17 at 12:36
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    @AndrewMorton -- that's not an issue if the two rods are solidly bonded together. The reason why two isolated rods can have a high potential difference in a lightning scenario is because the conductivity of ground is quite poor compared to that of #6 copper wire -- in effect, what's going on here is that the potential difference between the two rods is "shorted out" by the grounding system. – ThreePhaseEel Mar 10 '17 at 12:47
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    What you are calling the main panel is really a sub-panel, and should have a 4 wire feeder from the breaker under the meter, which in this case is the actual main panel. Your additional ground rod should connect back to that main breakers panel, even if it's just a single breaker enclosure. – Tyson Mar 10 '17 at 13:05
  • @ThreePhaseEel Thanks, the information regarding the relatively low conductivity of the ground is a good point. – Andrew Morton Mar 10 '17 at 14:36
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NEC requires the bonding electrodes be connected via an approved method if joined together outside an approved assembly like the main disconnects bonding lugs. In other words, you might have done it correctly assuming the main disconnect is actually in doors and not outdoors, and it had a free lug opened. If there were not any free lugs available then it would need to be secured via an approved method.

Adding two new ground rods ( 6 ft a part is Code ) would be ideal and leave the old one buried and unused. Though as mentioned by Ecnerwal it would not hurt anything to leave it connected. I say disconnect it as the next home owner will just be confused.

Edit

Additional info has came to my attention in that your drawing shows a box below the meter. This is typical of a main disconnect. Just to be clear, the panel inside would not be considered the main disconnect if there was already one outside. If this is the case then connecting the grounding electrode would only be acceptable at the main disconnect and not the panel inside.

Also, Code only requires one 8 ft ground rod if the minumin 25 ohms is met. It is easier to drive two ( Code says 6 ft a part ) and not bother testing if the 25 ohms is reached.

  • Which is the "main panel" as drawn above? – Tyson Mar 10 '17 at 14:24
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    There is no benefit to disconnecting the original rod. – Ecnerwal Mar 10 '17 at 15:37

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