Can anyone tell me what year the requirement for grounding source of the electrical system went from a single source to a dual source?
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Can you explain what you mean by single source and dual source? Do you mean one versus two electrodes?
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It would also help to tell what the current grounding is. A CEE or Ufer does not require a secondary ground. If a single rod has proven resistance of 25 ohms or less it does not require another either. A metallic water line does require a supplementary electrode.
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Is he thinking abut this?
NEC 250.56 requires that, where a single grounding electrode consisting of a rod doesn’t have a resistance to ground of 25 ohms or less, it must be augmented by one additional electrode
Thanks for all your responses. I am not well read on electrical codes and am struggling to get good answers. I was referring to the grounding “sources” ie: Water Service Piping, Ground Rods, & Ufer systems. California codes are fairly consistent with the NEC, but vary from city to city. And I can’t seem to get a consistent answer from even licensed electricians on the matter. The grounding system, as I understand it, must have two sources ie: 2 ground rods at 6ft apart, Water Service plus 1 ground rod. (Ufer - Not clear on this one if a secondary is required). This may be due to the dry climate in SoCal and earth is often very dry. Anyway, the reason I asked my original question was that I was informed by a fellow local inspector (30+ years) that this requirement for secondary grounding was adopted sometime around 1990. I can’t find anything on this, which leaves me asking: If the home was built prior to 1990 (or whatever the actual year was), and the electrical system has not been updated, is the property exempt from this code? Like I said, I can’t get a clear answer on this, and was hoping somebody out there was more educated than I am on the subject.
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I am performing a home inspection, not a code inspection.
I believe the NEC two rod rule was 2005.
Robert or Jim may be able to tell ya more.
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Let’s start with some terminology so that we’re all on the same page as the NEC. The “sources” you’ve mentions are called Grounding Electrodes and there are a list of them in the NEC that are used to make up a Grounding Electrode System (GES). Some electrodes cannot stand alone and are required to be supplemented by an additional electrode. The metal water pipe electrode is one that requires to be supplemented, this is typically done by installing two 8’ ground rods a minimum of 6’ apart (or one ground rod with a proven resistance of 25Ω or less). If there is a CEE (concrete encased electrode) and a plastic water pipe then no other electrodes are required because the CEE can be a stand alone electrode.
IMO the required electrodes from when the service was installed and inspected are all that need be in place during the time of the home inspection.
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Thanks Marc, and your comment about “not a code inspection” is my motto. That is why I refrain from ever using the word “code” in my comments and clearly disclaim that “The inspection is not for code compliance”. But as you know, we do have to dance around the code book when it comes to safety. Also, I have never tested resistance (Ohm readings) on the grounding system. Do you? I think that goes well beyond the visual review of the inspection. However, I do use moisture meters and voltage sniffers. Again, we have to walk a thin line.
IMO we don’t have to dance around it.
Just refer to it as a reference. 
No I don’t think any of us test resistance.
Keep in mind, a home inspection is not a code compliance inspection and that the Authority Having Jurisdiction (AHJ) is the responsible party for determining/verifying code compliance. The home inspector is using these standards, however, as a reference to help protect his or her client from possible future hazards, such as a house fire.
Thanks Robert, great information. But this again contradicts with what I’ve been told locally. The information I got from a long time inspector in the area is that only a single secondary electrode (grounding rod) is required if the water piping is also used as a grounding electrode. Otherwise, 2 electrodes (grounding rods) spaced 6 feet apart are required. However, most newer homes have CEE or Ufer grounds, which are not observable. And what you are saying is that no secondary electrode is required for these systems. So when I inspect a property which is grounded to the water piping (usually at the service or the water heater supply), then I should be calling out the missing secondary electrode. But if no grounding is observed (water piping or grounding rods) then I can only report that the grounding could not be verified, given that it may be provided with a CEE. Electrical is not my strong suit, but I’m eager to learn.
The part in bold is likely incorrect and here’s why, as I mentioned in my previous post in order for a single ground rod to qualify as an electrode it must be tested to prove that’s it’s 25Ω or less. If it has not be tested then a single rod is not an electrode, if it doesn’t qualify as an electrode then the single rod cannot solely be used to supplement the water pipe.
Around here anyone using rod electrodes just uses two because the 25Ω limit does not apply when there are two rods and rod testing can be expansive if you need to pay a third party or have to buy the proper testing equipment. Another reason is that single rods are typically not used is that depending on the soil conditions many areas cannot get a single rod under 25Ω so even if you did test it it would still require a second rod anyway.
If there is a metal water pipe then it requires a supplemental electrode which can be a CEE.
And finally, a CEE without a metal water pipe is the only electrode required.
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I’ve read on this MB about the two ground rod requirement for several years just never said anything.
In the five plus counties I serve, with dozens of AHJ’s and at last three different power companies, I rarely (almost never) see more than one ground rod, and it’s usually a stand alone grounding electrode.
Why that is the norm I don’t know.
It could just a local accepted practice or maybe in your area the soil conditions will consistently get the resistance of a single rod at 25Ω or less so no one bothers to test them. This has been an NEC requirement for decades.
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Probably so. I know it’s been an NEC requirement, it’s in all the courses I’ve taken over the years. It’s just always baffled me why it’s not enforced that way around here. I’ve never gotten a straight answer from anyone in my area.
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Same here in Ohio, I have never seen more than 1 ground rod, I’m thinking it’s the soils in our areas. Around here we have lot’s of clay and rich soil and for the most part no sand.
Although if there is a metallic water line I will many times ALSO see a grounding electrode attached there as well.
Attached is a 1 year warranty inspection I did last week.
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Looks pretty standard #2 aluminum GEC to the water pipe and the #6 solid to the ground rod. Still don’t know why someone would run #6 solid. 
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