Concrete encased electrode

[e2me2]

OK so now i hit the big concrete electrote debate full on
I have a 600A service on a apt building
I have plastic water line into building
I have concrete encased electrode hit with #4 largest required by 250.66B
I have a #6 to my ground rod as per 250.66A

and suddenly my 2/0 GEC that usualy hits my copper water line gets to disapper. and is replaced by a #4 to a concrete electrode ??? how can this be right maybe a code oversight

 

[iwire]

It's correct.

Why did you install a rod?

 

[winnie]

Do you have a metallic water piping system that needs to be bonded? With a plastic water service, you don't run a gec, but with internal metal piping you still bond per table 250.66. See 250.104.

-Jon

 

[e2me2]

Do you have a metallic water piping system that needs to be bonded? With a plastic water service, you don't run a gec, but with internal metal piping you still bond per table 250.66. See 250.104.

-Jon

No I have a metal meter and about 3 ' of coper on load side of mete then all plastic Im not going to spend $500 to bond 3' of copper pipe in a room were it would be next to impossiable for it to become energized
however I still dont understand why if i bring a GEC to water pipe as my only GEC it has to be #2 for 600 amp but if i use a concrete encased electrode as my only GEC it only has to be a #4why would you not have to use 250.66 for any grounding electrode

 

[hornetd]

No I have a metal meter and about 3 ' of coper on load side of mete then all plastic Im not going to spend $500 to bond 3' of copper pipe in a room were it would be next to impossiable for it to become energized
however I still dont understand why if i bring a GEC to water pipe as my only GEC it has to be #2 for 600 amp but if i use a concrete encased electrode as my only GEC it only has to be a #4why would you not have to use 250.66 for any grounding electrode

The code panel recognized that a concrete encased electrode is unlikely to carry current under normal operating conditions but an underground metal water pipe is likely to carry such current.

 

[bphgravity]

There's nearly no rhyme or reason for many of the grounding electrode system requirements in the NEC. It's not a code oversight. The problem is that the requirements and substantiation for the requirements are so old that no one is around anymore that can remember why the rule was placed in the code, so no one today on the CMP's are willing to consider changing these outdated requirements.

There is no money to be made by removing requirements from the code so no one is working on studies or research directly related to understanding the purpose and function of electrical system grounding. It's still assumed that if it worked for telegraph systems, it must still work today.

In the long term, I see little change occurring in Article 250 other than reorganization of the sections and correction in some terminology. So instead of making electrical grounding system make sense, they will simply add other technologies as code requirements to compensate for the lack of function grounding provides. GFCI's, AFCI's, and TVSS's are all evidence that electricity is not made safe by simply grounding materials and equipment.

 

[haskindm]

It is simple, whether you are using the water pipe as a grounding electrode, or are just bonding a metal piping system to the service, a metal waterline may be required to carry fault current. With the relatively high resisitance of a grounding electrode, it will not carry fault current. There is no point in installing a high amperage cable for a system that cannot develop high amperage. The code panel recognizes this so they require smaller conductors to the grounding electrode. Remember, a conductor carrying 120-volts, directly connected to a ground rod with 25-ohms resistance will only "see" 4.8-amps. How big does the conductor need to be to carry 4.8-amps? On the other hand a direct short to a waterline may need to carry hundreds of amps until the overcurrent device clears.
Thanks,

 

[bkludecke]

I asked the question once. I had a 2000amp service for a pumping plant (all plastic piping) out in a field. The concrete foundation had no uffer so we drove a couple of ground rods and ran #6 GEC to them. OK? Yup! Because the rods can only dissipate an amount of energy (lightning strike) which can easily be carried by the #6. Same is true for the #4 to a uffer. I got this from the EE on the project.