Lightning protection vs. servise grounding

[ryan_618]

Although I have never read the NFPA 780, I am led to believe that (in addition to air terminals and down wires) two ground rods are considered effective for the purposes of lightning protection.

My question is, if the grounding electrode system's main purpose is lightning protection, why do we have to have water pipes + building steel + concrete encased electrodes for this purpose, when two ground rods are considered effective by the 780??? Does anyone else see this as a silly waste of resources?

 

[dereckbc]

Re: Lightning protection vs. servise grounding

I don't think you are comparing apples to apples. 780 requires a ground rod at each down conductor, which is a minimum of two down conductors on each end a small structure like a house with a gable roof.

In all 780 systems I have been involved with the down conductor ground rods are separate or additional to NEC requirements, but have to be bonded.

 

[bphgravity]

Re: Lightning protection vs. servise grounding

Originally posted by ryan_618:
Does anyone else see this as a silly waste of resources?

I certainly do. And I plan on making it my life's work to prove it. I have recently submitted plans to my local building department to build two identical structures on some property I own here in SW Florida. Without getting into too many details, I plan on installing a service at each structure. One will have a complex grounding electrode system, the other will not have one at all. There will be some metering equipment involved and collection of data over several years of operation.

My thesis: There will be no discernable difference between the power quality, operation, or safety of either system.

 

[George Stolz]

Re: Lightning protection vs. servise grounding

Bryan, are you going to shoot lightning bolts at it?

How is it an effective demonstration, if you can't subject it to the conditions it's built for?

 

[bphgravity]

Re: Lightning protection vs. servise grounding

Well to start with, I live in the highest lightning occurance region in the entire nation.(>14 fl./km?/yr)

Second, that's the whole point. We ground services for something that might happen and/or for events that are quite uncommon. My point is the either structure is as likely to be struck by lightning or surged by high-voltage current. I believe the grounding system will do little to nothing to protect internal conductors and equipment. I find it likely the results are as variable as lightning itself. Here are some possible outcomes.

1. Neither structure receives damage
2. Both structures receive damage
3. The GES structure is damaged, the non-GES structure is not damaged
4. The non-GES structure is damaged, the GES structure is not damaged.

In short, the outcomes will be completely random at best. There is no way to indicate if, when, and how, a grounded system protects a structures electrical system.

I could only hope that both structures are effected by a lightning strike, and if luck is on my side, the grounded system structure will burn to the ground and the "non-protected" system structure holds up just fine.