Grounding loop

[hurk27]

Re: Grounding loop

By Charlie B.: it tells me second that we are not required to bond them

I think 250.106 clearly requires us to bond the lightning protection electrode to the service electrode.

250.106 Lightning Protection Systems.
The lightning protection system ground terminals shall be bonded to the building or structure grounding electrode system.

[ December 22, 2005, 06:40 PM: Message edited by: hurk27 ]

 

[dereckbc]

Re: Grounding loop

Originally posted by hurk27:

250.106 Lightning Protection Systems.
The lightning protection system ground terminals shall be bonded to the building or structure grounding electrode system.

Thanks Wayne, I knew it was spelled out somewhere, I just got lazy and stopped before getting that far. Not only does the NEC require it to be bonded but so does NFPA 780, UL-96 Master Label program, and any insurance company giving credit on UL Master Label

 

[hurk27]

Re: Grounding loop

Actually Bryan was the first to point it out.

BY Bryan: Check out 250.106

Now all we have to do is convince Charlie B.

 

[dereckbc]

Re: Grounding loop

Originally posted by hurk27:
Actually Bryan was the first to point it out.

Not my night, I blew right past it, Sorry Bryan, Oh well...

 

[hurk27]

Re: Grounding loop

I should point out that the use of the term "ground terminals" in 250.106 might confuse some. This is the term use for a grounding electrode in a lightning protection system as the spikes on the roof is called "air terminals"

 

[LarryFine]

Re: Grounding loop

Originally posted by Tom.Margillo:
Why is it necessary to put a ground loop around a building or structure. 4/0 bare copper around a building with ground rods every 20' then off of every other steel column a 4/0 cad-welded tieing into the loop.

Think of it like a giant equipotential grid around a swimming pool. The idea is to minimize the liklihood of current flow (and heat damage from the resulting voltage drop) due to a voltage difference.

Even with resistances in fractions of an Ohm, ultra-high currents, like from bolted faults and lightning strikes, can induce appreciable currents in structural and other metallic parts and systems.

 

[Tom.Margillo]

Re: Grounding loop

Is it permitted to bond the lightning protection to the building steel instead of going all the way to the earth? If the two loops have to bonded together like 250.106 says should be ok.

 

[steve66]

Re: Grounding loop

Is it permitted to bond the lightning protection to the building steel instead of going all the way to the earth? If the two loops have to bonded together like 250.106 says should be ok.

I not sure if bonding them to the building steel is permitted, but you want to be very careful that the bonding of the two systems (lightning and electrical) is done in a spot that keeps any potential lightning strikes from flowing on your electrical ground system. You don't want to direct a lightning strike through your grounding electrode conductors.

I think this is normally done by keeping the two ground systems separate, and then bonding them underground with a smaller wire. That way, there is no chance a lightning strike will burn open the main GEC.

Steve

 

[charlie b]

Re: Grounding loop

Originally posted by iwire: I can not understand your position.

If the lightning protection system uses electrodes that fit the descriptions in 250.52(A)(1) through (A)(6) then IMO they must be bonded to the service electrodes.

My position was simply that the NEC appears to have conflicting language. But thank you Bryan for answering my question:

Originally posted by charlie b: 250.60 says that it does not prohibit you from bonding the building's GES to the lightning protection system's electrodes. What I do not know is what, if anything, requires it.

The answer is, as Bryan pointed out, 250.106.

But let's presume for a moment that that article did not exist. Then let's pose the question, "does 250.50 require bonding the building's GES to the any part of lightning protection system"? The reason I see a conflict here is that 250.60 is obviously treating the two as separate systems. You can't use the lighting protection system, in lieu of a GES. Also, you are not prohibited from connecting the two. "Not prohibited." That's a bit of a double negative. But I read it as meaning that we are allowed, but are not required, to connect (bond) the two systems. So 250.50 says to bond electrodes, but 250.60 says we don't have to bond the GES to the lightning protection system's electrodes. I conclude that we are left not knowing what is, and what is not, required.

 

[LarryFine]

Re: Grounding loop

Originally posted by charlie b:
I conclude that we are left not knowing what is, and what is not, required.

Gee, that's never happened before! :roll:

 

[hurk27]

Re: Grounding loop

Charlie B.

The reason I see a conflict here is that 250.60 is obviously treating the two as separate systems.

They are and the NEC does not want use to rely on just the electrodes for air terminals to be the sole electrode system for the electric system.
But if we look at 250.60 we see that it also makes referance to the requirment of bonding these two systems together.

This provision shall not prohibit the required bonding together of grounding electrodes of different systems.

And that "required bonding" is found in 250.106

This will somewhat work to keep the two systems close to the same potental in the event of a lightning strike. :roll: Yea right! but thats what I get from 250.50, 250.53(B), 250.60, And 250.106

[ December 24, 2005, 12:30 AM: Message edited by: hurk27 ]