Grounding system with rods only?

[Gilf]

Hi,

I am absolutely not sure about this, I'd appreciate any guidance that you can provide.

Attached 2.pdf is what would be the grounding/earthing(?!) system of an apron sunshade. In the previous design everthing was connected by a grounding grid (1.pdf). The problem was that the apron sunshade would be built on an existing concrete slab and the government would prefer to not saw cut the existing concrete. We were directed to provide a design analysis and if a single ground rod could suffice the required resistance, then remove the ground loop.

I am feeling absolutely uneasy about removing the ground loop as i'm afraid that it could create a huge rise in potential diffence if lightning strikes.

On the other hand I couldn't find a section in code (both NFPA and BS codes) that clearly states that these rods must be connected together, or i'm not understanding it. As i search more more i'm even more confused yet i still feel very uneasy about removing the ground loop.

Thanks in advance!

 

[iwire]

If lightning strikes the structure there is going to be a large potential regardless of what type of electrode you provide.

 

[petersonra]

On the other hand I couldn't find a section in code (both NFPA and BS codes) that clearly states that these rods must be connected together, or i'm not understanding it. As i search more more i'm even more confused yet i still feel very uneasy about removing the ground loop.

Thanks in advance!

The code is pretty clear about requiring all available grounding electrodes be bonded together. The code does not require a ground loop as such. However, just because you pound a rod in the ground does not make it a grounding electrode as it has to meet the requirements the code has for ground rods (size, length, material, depth of pounding, etc.). However if it does meet those requirements the code requires it be bonded into the grounding electrode system.

This appears to be more of a lightning protection system and thus whatever bonding and grounding requirements there are can be above and beyond what is in the code, but minimum code requirements still apply.

 

[GoldDigger]

If electrical equipment attached to or touching the sunshade were to fault to it, a ground rod would not be a viable fault current path to trip OCPD. For that reason, IF the structure is considered likely to become energized by the AHJ it has to be bonded to an EGC.

 

[Smart $]

If the sunshade is an interconnected steel-framed structure, your ground rods are connected through the structural steel [NEC 250.68(C)(2)]. Not quite as good as with the ground ring (aka grid), but it is sufficient per Code.