"If available on the premises ..."

[jrturner]

Article 250.50 states that "If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system."

Given this code requirement and the fact that a new building or structure should have most if not all of the items in 250.52(A)(1)-(A)(6) available; why do most electricians/engineers utilize/specify (1)the underground water pipe, (2) the metal building frame and (5) rod electrode and forget about (3) concrete-encased electrode, (4) ground ring, and (6) plate electrodes?

Also, I commonly see the triad configuration of ground rods with no memtion of this in the code. What purpose does it serve if a #6 copper is all that's required to a single ground rod? The #6 can only carry an amount of current that can be dissipated into the ground by single ground rod within a specific time period. Adding rods won't help unless the #6 is increased in size. Please explain.

 

[websparky]

Re: "If available on the premises ..."

(3) concrete-encased electrode, (4) ground ring, and (6) plate electrodes?

These electrodes are not always available at new buildings unless the engineer specifies them.

The code only requires a minimum of two electrodes. Usually, water pipe is always there and the rods can always be added. If the building is steel, then it would be included too.

The idea behind the multiple rods is to be sure that you meet the 25 ohm requirement. After two rods, I guess it is just extra insurance?

 

[dereckbc]

Re: "If available on the premises ..."

Originally posted by jrturner:
Given this code requirement and the fact that a new building or structure should have most if not all of the items in 250.52(A)(1)-(A)(6) available; why do most electricians/engineers utilize/specify (1)the underground water pipe, (2) the metal building frame and (5) rod electrode and forget about (3) concrete-encased electrode, (4) ground ring, and (6) plate electrodes?

It really comes down to the RFQ job specifications. For example; if a RFQ is received and states "the grounding electrode system shall meet minimum NEC requirements". The EC is only going to provide the minimum of a water pipe and two ground rods. If he/she arrives and finds a UFER and building steel available, the EC will have to use it, and could drop the ground rods in place of the UFER to recover some of the unforeseen cost.

On the other hand the engineer could specify the water pipe, UFER, building steel, and ground ring in the RFQ. The engineer could even require all GEC's and bonding conductors to be 750 MCM and thermally welded. It is a design issue rather than code.

Also, I commonly see the triad configuration of ground rods with no mention of this in the code. What purpose does it serve if a #6 copper is all that's required to a single ground rod? The #6 can only carry an amount of current that can be dissipated into the ground by single ground rod within a specific time period. Adding rods won't help unless the #6 is increased in size. Please explain.

A triad exceeds code requirements and is a design issue rather than a code issue. By using multiple rods spaced greater than 2 times the rod length lowers the overall impedance, thus increasing the amount of current vs. time period. Or in other words it raises the ground saturation value and lowers the overall ground rise potential.

[ October 29, 2003, 11:25 PM: Message edited by: dereckbc ]

 

[jrturner]

Re: "If available on the premises ..."

The code only requires a minimum of two electrodes.

The EC is only going to provide the minimum of a water pipe and two ground rods.

Where is it "specifically" stated in the code that only two electrodes are required? I realize that 250.53(D)(2) states that a metal underground water pipe shall be supplemented but that's not to say that the other electrodes shouldn't also be installed and bonded together. Again 250.50 states that ALL the electrodes in 250.52 must be bonded together where available. And again, if it's new construction there is no reason not to install all of them and have all of them available unless of course the building is wood frame construction with no water service. Still confused?

 

[ryan_618]

Re: "If available on the premises ..."

The code only requires one electrode, if it is the only one available. If the only one available is a water pipe, you must MAKE another one available.

If you have plastive pipe and a wood frame building, but just happened to install a Ufer...you are done.

 

[jrturner]

Re: "If available on the premises ..."

The code only requires one electrode, if it is the only one available.

The word "available" implies an existing condition. Again, for new construction most of the electrodes in 250.52 can and should be made "available" according to my interpretation of the code. It would be nice to get Mike Holt's thoughts on this issue!

 

[mike@mikeholt.com]

Re: "If available on the premises ..."

According to the NFPA Handbook.

Formal Interpretation 78-4
Reference: Article 250.50
Question: Is it the intent of 250.50 that reinforcing steel, if used in a building footing, must be made available for grounding?
Answer: No.
Issue Edition: 1978
Reference: 250-81
Issue Date: March 1980