Ground Rods, How many?

[2Big2Ride]

Just curious...

I have read many references here on GJ that that you need two (2) grounding rods installed on the exterior of your structure to comply with code. Of the three home owner style DYI books I have, one of them references two grounding rods are required. It also notes different diameters, one for 100 amp and less (1/2"), the other for greater than 100 amps (5/8").

Why I am curious? Our house was built in 1998, and the shop received electrical service in May 2012, both use a single ground rod. Both have 200 amp services. A licensed electrician installed the panel in the shop, pulled the required permits, and had the inspection before the PoCo provided the connection. Is it most likely we just live in an area that still uses older codes? If it was a code change from one ground rod to two, what year did it go in to effect? How important are two ground rods?

 

[Gooch]

Just curious...

I have read many references here on GJ that that you need two (2) grounding rods installed on the exterior of your structure to comply with code. Of the three home owner style DYI books I have, one of them references two grounding rods are required. It also notes different diameters, one for 100 amp and less (1/2"), the other for greater than 100 amps (5/8").

Why I am curious? Our house was built in 1998, and the shop received electrical service in May 2012, both use a single ground rod. Both have 200 amp services. A licensed electrician installed the panel in the shop, pulled the required permits, and had the inspection before the PoCo provided the connection. Is it most likely we just live in an area that still uses older codes? If it was a code change from one ground rod to two, what year did it go in to effect? How important are two ground rods?

The NEC Requires two ground rods if you can't prove that one results in 25ohms IIRC. Otherwise one is acceptable. Also the smallest ground rod the NEC recognizes is 5/8". Do you have any other supplemental ground rods(i.e. Under ground water pipe, concrete encased electrode, etc.)

 

[sparky36000]

The NEC Requires two ground rods if you can't prove that one results in 25ohms IIRC. Otherwise one is acceptable. Also the smallest ground rod the NEC recognizes is 5/8". Do you have any other supplemental ground rods(i.e. Under ground water pipe, concrete encased electrode, etc.)

1/2" rods are acceptable if listed.

NEC 250.52(A)(6)

(6) Other Listed Electrodes. Other listed grounding electrodes
shall be permitted.

The requirement changed a few years ago. Most shops don't bother with testing for the 25ohms or less and just drive the second rod. If it doesn't pass, you have to drive it anyway.

 

[2Big2Ride]

The NEC Requires two ground rods if you can't prove that one results in 25ohms IIRC. Otherwise one is acceptable. Also the smallest ground rod the NEC recognizes is 5/8". Do you have any other supplemental ground rods(i.e. Under ground water pipe, concrete encased electrode, etc.)

Both the house and shop ground rod measure just under 5/8", a little over 9/16" (15mm).

The shop doesn't have an underground water pipe, or a concrete encased electrode. The construction is welded metal frame and it is is connected to ground on the vertical I-beam right next to the service panel.

Not certain on the house, but the house does have the copper cold water grounded at the water heater that is very close to the service panel. The water supply to the house is all in plastic, internal cold and hot lines are all copper and they go in and out of the slab foundation in many places.

 

[Air_Cooled_Nut]

My 1960 house only had one, which I had installed new in mid-2000 to meet code. Prior to that there was none but the house did have all-metal plumbing. Now about 3/4 of the plumbing is metal. So probably depends on local ordinances.