Grounding - well casting as electrode?

[factoryrat]

On this question you can choose more than one answer.

Exam Question: You are connecting power to a small pump house. You intend to use the metal well casing as a grounding electrode for the remote
structure and the casing is isolated from the house supply, a metal water pipe. You would -


a.) use the well casing as the grounding electrode
b.) must effectively bond the pipe to the well casing
c.) may not use the well casing as an electrode
d.) need to add a supplemental grounding electrode as part of the system

Help! I'm confused and could use some direction.
Thanks

 

[raider1]

Take a look at 250.52(A)(7) if you are using the 2005 NEC or 250.52(A)(8) if you are using the 2008 NEC.

Chris

 

[factoryrat]

Thanks for quick response.

I'm using 2005 NEC.

"250.52 Grounding Electrodes
(A) Electrodes Permitted for Grounding
(7) Other Local Metal Underground Systems or Structures
Other local metal underground systems or structures such as piping systems, underground tanks, and underground metal well casings that are not effectively bonded to a metal water pipe."

I have looked at 250:52(A)(7). And does that mean I can't use answer: b.)must effectively bond the pipe to the well casing.? And do I need to add a supplemental grounding electrode as part of the system?

 

[raider1]

My answer would be C.

You are only permitted to use well casing as a grounding electrode if none of the electrodes in 250.52(A)(1) through (A)(6) are not present. (See 250.50) The question states that the supply to the house is a metal water pipe. If that is the case the pump house would have a metal underground water pipe that is present and that must be utilized for the grounding electrode in accordance with 250.50 and the requirements of 250.53(D).

Now if the metal water pipe that feeds the house doesen't fit the requirement to be a grounding electrode in accordance with 250.52(A)(1) then you could use the well casing for a grounding electrode because it is islolated from the metal water pipe.

Also there is no requirement to supplement a well casing used as a grounding electrode with another grounding electrode.

This is not a very well worded question, IMHO.

Chris

 

[factoryrat]

“250.52 Grounding Electrodes
(A) Electrodes Permitted for Grounding
(1) Metal Underground Water Pipe
A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing effectively bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors. Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.”

What if the water pipe met the above requirements? Couldn’t the well casing be bonded to the water pipe to form the grounding electrode? Which would be answers: a.) & c.)?

 

[Dennis Alwon]

But I could use it as a supplementary electrode instead of driving a ground rod. No?