Lightning Electrode Depth

[masterelect1]

NFPA780 - 4.13.4 states that a ground ring electrode must be buried at a depth of 18".

Can anyone elaborate on the potential hazards/consequences of burying the "ring" less than 18", e.g. 8"-10"

Thanks
John

 

[haskindm]

It would not be considered a grounding electrode per article 250. It would also be subject to damage from shallow digging. It could be treated as an auxiliary (2008 wording) electrode.

 

[bphgravity]

In addition to the comments given by haskindm, the idea is to ensure the conductor has sufficient surface area contact with earth. By installing the conductor at least 18" below grade, you establish uninterruptible soil contact from all directions; in effect the weight of the 18" of soil is sufficient to compact around the conductor at that depth. While this may be accomplished at lesser depths, there is a chance that the conductor will not maintain good contact with the earth when relatively close to the surface of the earth.

 

[masterelect1]

In addition to the comments given by haskindm, the idea is to ensure the conductor has sufficient surface area contact with earth. By installing the conductor at least 18" below grade, you establish uninterruptible soil contact from all directions; in effect the weight of the 18" of soil is sufficient to compact around the conductor at that depth. While this may be accomplished at lesser depths, there is a chance that the conductor will not maintain good contact with the earth when relatively close to the surface of the earth.

I understand that part. My question is: does anyone have any first hand experience regarding what has happened when there is a lightning strike and the ring is not deep enough.

Thanks
John

 

[bphgravity]

Probably not. There is a huge amount of research and documentation on the effectiveness and performance of grounding systems used on lightning protection systems. For the most part, they only include systems that are installed to a minimum standard or code.

I personally doubt you would be able to calculate or determine the performance of the entire system has been or will be compromised if the burial depth of the electrode does not exactly meet the minimum requirements.

Too many variables.

Keep in mind that many installations on rock or other solid ground have grounding systems that sit on the surface of the earth. These systems have been shown to be very effective when installed properly.

 

[masterelect1]

Probably not. There is a huge amount of research and documentation on the effectiveness and performance of grounding systems used on lightning protection systems. For the most part, they only include systems that are installed to a minimum standard or code.

I personally doubt you would be able to calculate or determine the performance of the entire system has been or will be compromised if the burial depth of the electrode does not exactly meet the minimum requirements.

Too many variables.

Keep in mind that many installations on rock or other solid ground have grounding systems that sit on the surface of the earth. These systems have been shown to be very effective when installed properly.

Thanks for the reply--- Had the EC just done the damn installation as required as per NFPA780, this post would have been unnecessary!!

Thanks
John