two means of ground

[difowler44]

In an course I took, they said that we had to have two means of ground on a new residence. The secondary means of ground would be the ground rod. The primary had to be a ground ring, or plate, or concrete encased ground, etc. I tried to find that rule under 250 recently, but can not find where it says, "you must have two grounds on a new residence". Anyone know where it is?

 

[augie47]

You will not find such wording. 250.50 will tell you all grounding electrodes present must be utilized, but you will need to research all of 250 Part III to see which ones are "stand alone"

 

[ericsherman37]

You might have some sort of local code that requires it. For example, here in Oregon, any structure with reinforced concrete foundation is required to have a ufer. House? Needs a ufer. Sewer plant? Needs a ufer. Skyscraper? Needs a ufer.

The NEC does require supplemental grounding if you utilize stuff like metal underground water pipe as an electrode. Check out 250.53.

 

[infinity]

The statement two means of ground is incorrect. There are many different scenarios regarding a grounding electrode system. As Augie stated you must use all qualifying electrodes that are present. Only the water pipe electrode requires a supplemental or second electrode. A building with just a CEE (no metallic water pipe) would require nothing more than the CEE.

 

[Minuteman]

The statement two means of ground is incorrect. There are many different scenarios regarding a grounding electrode system. As Augie stated you must use all qualifying electrodes that are present. Only the water pipe electrode requires a supplemental or second electrode. A building with just a CEE (no metallic water pipe) would require nothing more than the CEE.

But for local amendments.

 

[infinity]

But for local amendments.

True, local amendments will trump the NEC, but for our discussion here unless a local amendment is mentioned specifically there is an assumption that there isn't any.

 

[ceb58]

The statement two means of ground is incorrect. There are many different scenarios regarding a grounding electrode system. As Augie stated you must use all qualifying electrodes that are present. Only the water pipe electrode requires a supplemental or second electrode. A building with just a CEE (no metallic water pipe) would require nothing more than the CEE.

Or there may be a misunderstanding of what was said. Some one may have been referring to 250.56. As it has been discussed here more than once. If using only ground rods it has been common practice to drive two rods and be done with it due to the cost and coordination of testing one rod for less than 25ohms