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Temp Service and Two Ground Rods - What is Required?

jar546

jar546

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NEC 250.53 Covers the necessity for a supplemental ground rod or in reality a supplemental grounding electrode. What if the POCO only shows one on their detail for a temp service? Do you follow the minimum standards of the NEC or do you only require what is shown on the electric utility's diagram?

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My understanding is that the power company is regulated by the Public Utility Commission and not by the local jurisdiction, at least in California. The question is who has jurisdiction. The figure and the notes seem to infer that the PUC rules apply. Consistent with the notes and the fact that the ground rod shown is after the meter I would assume that the local electrical code applies if it is more restrictive.

The intent of grounding is that the resistance of the ground is below a given resistance. If the ground resistance is below this value there is no need for additional grounding rods. The problem is that in order to measure the ground resistance you will need more than one ground rod. While multiple ground rods may allow you to measure the resistance just providing multiple ground rods does not guarantee that the resistance is low enough. But if somebody has already done some testing one rod may be adequate.
 
Mark K said:
My understanding is that the power company is regulated by the Public Utility Commission and not by the local jurisdiction, at least in California. The question is who has jurisdiction. The figure and the notes seem to infer that the PUC rules apply. Consistent with the notes and the fact that the ground rod shown is after the meter I would assume that the local electrical code applies if it is more restrictive.

The intent of grounding is that the resistance of the ground is below a given resistance. If the ground resistance is below this value there is no need for additional grounding rods. The problem is that in order to measure the ground resistance you will need more than one ground rod. While multiple ground rods may allow you to measure the resistance just providing multiple ground rods does not guarantee that the resistance is low enough. But if somebody has already done some testing one rod may be adequate.
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The installation, other than the lateral coming from the utility pole and the meter itself are the responsibility of the permit holder. The permit holder is bound to comply with NFPA 70 so the two ground rods are required unless they can prove less than 25 ohms to earth. The POCO does not take responsibility for the installation by others. The minimum requirement by the POCO is what they expect in order to connect to a temp service. Just because they are showing 1 ground rod, does not mean the electrician does not have to comply with the NEC. Essentially the temp service is not part of their utility system that allows them to do what they want.
 
The POCO authority stops at the end of the drop or lateral when it comes to the mechanics of the installation. That doesn’t mean that the POCO is out of the loop on the proposed scale and use of the electricity.

I have seen the POCO violate CEC and the customer gets upset. One of the worst is when the meter is spotted where it can’t be …. With swimming pools is one. And then the Edison planner tries to talk me into allowing a panel four feet from the pool.
 
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