Two ground rods

[domnic]

What was the first code cycle to mandate two ground rods ????????????????????????????????????????????????????????????????????????????????

 

[curt swartz]

There is no code that requires 2 ground rods. Its an option when using trying to use one rod as the grounding electrode but not a requirement!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[goldstar]

Most of us juat drive the second rod so that we don't have to make the $$$ investment into a meter that can prove to the EI that the 1st rod has 25 ohms or less to ground. Stupid rule and a waste of time and $$$ IMHO BUT - Rules is Rules.

 

[infinity]

The 25Ω resistance has been required for decades. I looked back as far as the 1940 NEC and it says:

1913 (2584) Resistance of Buried or Driven Electrodes. Buried or driven electrodes shall, where practicable, have a resistance to ground not to exceed 25 ohms. Where the resistance is not as low as 25 ohms, two or more electrodes connected in parallel shall be used.

 

[goldstar]

The 25Ω resistance has been required for decades. I looked back as far as the 1940 NEC and it says:

Understood. When did EI's start requiring that you PROVE that installing only 1 rod was 25 ohms or less to ground ? Are we to ASSUME that driving the 2nd rod coupled with the first is actually 25 ohms or less to ground ? Why don't we have to prove that as well ? Will we eventually be going to 3 or 4 rods ? The rod(s) is a SUPPLEMENT to the water line ground. Sorry for being so blunt but I just think it's something an EI can break your chops about and demonstrate his authority. Just my opinion.

 

[infinity]

Understood. When did EI's start requiring that you PROVE that installing only 1 rod was 25 ohms or less to ground ? Are we to ASSUME that driving the 2nd rod coupled with the first is actually 25 ohms or less to ground ? Why don't we have to prove that as well ? Will we eventually be going to 3 or 4 rods ? The rod(s) is a SUPPLEMENT to the water line ground. Sorry for being so blunt but I just think it's something an EI can break your chops about and demonstrate his authority. Just my opinion.

Here in NJ it started somewhere in the mid-90's. I remember getting permit for a service upgrade and they handed me a piece of paper (I think from the DCA) that stated that two rods would be required or testing for 25Ω or less. IMO we will never be required to go beyond the use of two rods without a requirement for 25Ω or less testing.

 

[tom baker]

Understood. When did EI's start requiring that you PROVE that installing only 1 rod was 25 ohms or less to ground ? Are we to ASSUME that driving the 2nd rod coupled with the first is actually 25 ohms or less to ground ? Why don't we have to prove that as well ? Will we eventually be going to 3 or 4 rods ? The rod(s) is a SUPPLEMENT to the water line ground. Sorry for being so blunt but I just think it's something an EI can break your chops about and demonstrate his authority. Just my opinion.

Requirements for ground rods were added many years ago, likely from research from IEEE. Grounding electrodes are for protection from lightning, contact with HV lines and to stabilize voltage to earth. Using 2 rods is most cost effective. Its not likely to see a requirement to go to 3 or 4 as there is little benefit with 3 or 4. The answer to your whys may be in NFPA archives. In all the research I have done at IEEE I never found an article on ground rods, 25 ohms etc (I did a search for grounding and purchased many articles)

 

[goldstar]

Thanks Tom and thanks for the graph. It's interesting to see in fig # 12 that someone, somewhere along the line actually thought about the 3rd and 4th rod.

 

[goldstar]

The 25Ω resistance has been required for decades. I looked back as far as the 1940 NEC and it says:

I just re-read your post #4 and part of your quote stated

Where the resistance is not as low as 25 ohms, two or more electrodes connected in parallel shall be used.

As I mentioned in post # 8 in response to Tom that someone, somewhere along the line actually thought about the 3rd and 4th rod. So, again I started thinking that somewhere along the line an EI is going to ask to prove that the 2nd rod is actually providing 25 ohms to ground. Hopefully the NJ-DCA will stand with the EC's and not require this (and if they do I hope I'm retired by that time).

 

[Fred B]

I recall a MH video that he did testing ground resistance (and evidently had soil conditions to do it), that he had driven end to end welded rod reaching very deep (if memory serves approaching 100ft). Even that only had moderate gains in lowering the resistance. Not sure exactly where and what the video was related to.

 

[tortuga]

The 1918 is the first NEC that requires the additional groundrod if driven rod does not have resistance of 25 ohms or less. Rule 15A paragraph t.
There also was a requirement that water pipe electrodes should not exceed 3 ohms.

 

[garbo]

Thanks Tom and thanks for the graph. It's interesting to see in fig # 12 that someone, somewhere along the line actually thought about the 3rd and 4th rod.

Mike Holt did a great vidio at his home a few years ago. He did not get the magical 25 ohms until he screwed at least 5 eight foot long ground together so had to reach 40' deep to get 25 ohms. Many years ago I drove a 8' ground rod into moist soil and attempted to light a 100 watt incandescent lamp. Then 25 watt lamp. Looked as dim as a pen light with very old batteries.Only a slight glow. Firmly believe that if you have a copper water service, cast iron waste line & metal gas pipe service a second ground rod is a waste. After upgrading services to 200 Amps along with two 8' ground rods spaced 10' apart a few times took out my largest clamp on amp meter and read at least 0.25 amps on 3/4" copper water service & a lesser amount on steel gas pipe service along with no current on ground rods.

 

[Jpflex]

What was the first code cycle to mandate two ground rods ????????????????????????????????????????????????????????????????????????????????

What was the first code cycle to mandate two ground rods ????????????????????????????????????????????????????????????????????????????????

It is required to use two ground rods for dwellings. One being main and supplemental within I think 8 feet from the first.

However, there is an exemption to allow only one if the rod is 25 ohms to less to earth. You’ll have to test it

 

[retirede]

It is required to use two ground rods for dwellings. One being main and supplemental within I think 8 feet from the first.

However, there is an exemption to allow only one if the rod is 25 ohms to less to earth. You’ll have to test it

The two rods together comprise the grounding electrode system. One is not supplemental.

 

[Jpflex]

The two rods together comprise the grounding electrode system. One is not supplemental.

One electrode cannot be supplemental but two includes this. Code says If resistance is less than 25 ohm to ground an additional must be used - whatever that means

 

[goldstar]

One electrode cannot be supplemental but two includes this. Code says If resistance is less than 25 ohm to ground an additional must be used - whatever that means

Understood. But the problem is PROVING that it’s 25 ohms

 

[Jpflex]

Understood. But the problem is PROVING that it’s 25

 

[Jpflex]

So code means 2 electrodes are required if under 25 ohms but if not 3 are required?

 

[nizak]

Only once in almost 30 years do I recall an EI test grounding electrode resistance. He was the only one I ever recall having a clamp around digital meter.

 

[goldstar]

Only once in almost 30 years do I recall an EI test grounding electrode resistance. He was the only one I ever recall having a clamp around digital meter.

And I'll bet that was an expensive meter provided by the municipality he works for. It's not a meter that an EC would buy just to prove the rod is 25 ohms or less. That's really the whole point to this argument. Why get into a go-around with an EI when driving the 2nd rod eliminates that.