LP Loop

[Alwayslearningelec]

So we’re being asked to size the lighting protection grounding loop. I attached picture of top of building and bottom so you can get feel of wats’ involved.

Each floor has 3 ground bars.

Some of the down conductors are tying into the LP grounding loop an theres also a tie from the LP grounding loop to the main switchgear room ground bar.

Is there a calculation to size the LP grounding conductor?

 

[Alwayslearningelec]

Also what determines the following regrading the ground loop around the entire building?
1. How often are ground rods required around the building that tie into the ground loop?
2. How often to you tie the ground loop to building steel column?

Thanks.

 

[petersonra]

Also what determines the following regrading the ground loop around the entire building?
1. How often are ground rods required around the building that tie into the ground loop?
2. How often to you tie the ground loop to building steel column?

Thanks.

The answers to these questions are to be found in the UL listed drawings the lightning protection contractor is required to provide.

Personally, I am not sure I would be tying the lightning protection down contactors to any ground bar inside the building. Sounds like a good way to get lightning to come inside the building.

I am not a lightning protection expert but I always thought the idea was to keep the lightning on the outside and not invite it in.

 

[RWC/NC.]

I don't currently have references w/me @ the moment, but your connection to your rooftop "air terminals" and cables associated w/LP system as memory serves, your LP cables need maintain a horizontal "minimum distance" separation of 6' (six foot) away from the other grounding system until exiting building, in connection to grounding electrode system ring (grid) encircling the structure, that maintains @ buried depth @ no less than 30" (thirty inches).
This is the allowed physical LP's tie connection to building grounding electrode system encircling the structure. The same grounding loop, buried in the earth serving the structure grounding electrode system. Maybe someone can expand their thoughts further in assistance of your question(s)..

 

[Alwayslearningelec]

Thank you. I'm curious as to how many ground rods are needed around building perimeter to tie into grounding loop and how often the ground loop needs to be tied into building steel.

 

[GoldDigger]

Thank you. I'm curious as to how many ground rods are needed around building perimeter to tie into grounding loop and how often the ground loop needs to be tied into building steel.

Unless there is a very steep soil conductivity increase with depth, I do not see any good reason for adding ground rods to a buried loop ground. The sphere of influence of the loop conductor will make the ground rod less of an incremental improvement.
Or are you referring to an above ground bonding loop that connects grounding electrodes?

The whole thing (tying to building steel in multiple points) seems to go against the design principle of a single point of contact between GES and the EGC system.

 

[Alwayslearningelec]

Unless there is a very steep soil conductivity increase with depth, I do not see any good reason for adding ground rods to a buried loop ground. The sphere of influence of the loop conductor will make the ground rod less of an incremental improvement.
Or are you referring to an above ground bonding loop that connects grounding electrodes?

The whole thing (tying to building steel in multiple points) seems to go against the design principle of a single point of contact between GES and the EGC system.

Referring to this ground loop below grade.