wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Hello again,
I'm starting a new thread as I couldn't post to the reopened thread "Additional Grounding Electrodes at Subpanel". I'll recap and expand on my question here:
I'm doing permitted work in California as an Owner/Builder towards my General Contractor's license, and I have a question about grounding electrodes at a subpanel. My residence has a 125A exterior service disconnect with a #1/0 Al SER feeding a MDP with separate ground and neutral about 30' away. At the disconnect the GES consists of a driven ground rod, the copper water service, and a concrete encased electrode (CEC), 20' of #4 Cu wire embedded in the foundation. At the MDP there is an additional 20' of #4 Cu wire embedded in the same foundation, which my electrician has connected to the MDP ground bar. Is this connection proper?
My thinking so far goes like this. First, should the #4 Cu lead at the MDP be considered a separate CEC, and will using it improve the GES? They are part of the same foundation and the rebar is continuous with splices between the two locations; I'm not sure how well if at all either lead is tied to the rebar. The foundation is about 4' deeper at the MDP, which should make for a lower resistance electrode.
So if the second #4 Cu lead is not useful, I'll just disconnect it. Otherwise, 250.54 allows a "supplementary grounding electrode" to be connected to the EGC system as has been done here. What exaclty does supplementary mean and does it apply here?
Lastly, if 250.54 doesn't apply, can the #2 Al EGC in the #1/0 SER feeder do double duty as a bonding jumper connecting the second CEC to the rest of the GES? This question was raised in the January 2007 thread "Combo GEC and EGC" but it seems like the thread didn't reach a definitive conclusion. From this point of view, I'm not sure if either the >20' distance to the main disconnect or the splice at the MDP ground bar would be a problem.
Any guidance would be apprecated. Thanks, Wayne
I'm starting a new thread as I couldn't post to the reopened thread "Additional Grounding Electrodes at Subpanel". I'll recap and expand on my question here:
I'm doing permitted work in California as an Owner/Builder towards my General Contractor's license, and I have a question about grounding electrodes at a subpanel. My residence has a 125A exterior service disconnect with a #1/0 Al SER feeding a MDP with separate ground and neutral about 30' away. At the disconnect the GES consists of a driven ground rod, the copper water service, and a concrete encased electrode (CEC), 20' of #4 Cu wire embedded in the foundation. At the MDP there is an additional 20' of #4 Cu wire embedded in the same foundation, which my electrician has connected to the MDP ground bar. Is this connection proper?
My thinking so far goes like this. First, should the #4 Cu lead at the MDP be considered a separate CEC, and will using it improve the GES? They are part of the same foundation and the rebar is continuous with splices between the two locations; I'm not sure how well if at all either lead is tied to the rebar. The foundation is about 4' deeper at the MDP, which should make for a lower resistance electrode.
So if the second #4 Cu lead is not useful, I'll just disconnect it. Otherwise, 250.54 allows a "supplementary grounding electrode" to be connected to the EGC system as has been done here. What exaclty does supplementary mean and does it apply here?
Lastly, if 250.54 doesn't apply, can the #2 Al EGC in the #1/0 SER feeder do double duty as a bonding jumper connecting the second CEC to the rest of the GES? This question was raised in the January 2007 thread "Combo GEC and EGC" but it seems like the thread didn't reach a definitive conclusion. From this point of view, I'm not sure if either the >20' distance to the main disconnect or the splice at the MDP ground bar would be a problem.
Any guidance would be apprecated. Thanks, Wayne
