Question about Lightning protection

[kingbambina]

Hi,

I have two questions regarding lightning protection arrestors and down conductors:



1. We have a gasoline loading bays and there is a grounding busbar for its instrumentation and lighting that's connected to the grounding grid. The canopies of these have lightning arrestors installed, and the down conductors are connected to the bay's existing busbar. Is this the in vialoations of NEC 250.60 or the NFPA 780?



2. Some of these arrestors have a relatively high resistance (more than 5 ohms). How can I bring it down?



Thanks

 

[che12345]

kingbambina (Electrical)(OP)11 Nov 23 07:25
".... #1. We have a gasoline loading bays and there is a grounding busbar for its instrumentation and lighting that's connected to the grounding grid. The canopies of these have lightning arrestors installed, and the down conductors are connected to the bay's existing busbar. Is this the in vialoations of NEC 250.60 or the NFPA 780? #2. Some of these arrestors have a relatively high resistance (more than 5 ohms). How can I bring it down?"
I have the following opinion for your consideration.
1. NEC 250.60 states Air terminal conductors and driven pipes, ....used for grounding air terminals shall not be used in lieu of the made grounding electrode requited by Section 240-52 for the grounding wiring systems....This provision shall not prohibit the required bonding together of electrodes of different systems. See also FPN....etc. It means that the air terminal shall have its own grounding electrode/system. Separated from the others. Two respective/separate systems is allowed to be bond together.
2. To lower the grounding resistance see NEC 250-52 . Plant the rod deeper but need not exceed 6m and space them >4m apart. Bond them together.
BTW Check whether lightning electrode resistance 5 Ohm is fine ?. Why need to be lowered?
Che Kuan Yau (Singapore)

 

[Kiribanda]

I am little confused here.
1) You have mentioned that the canopies have got LAs.
2) You have mentioned that those LAs have got down conductors too.
3) Are they lightning arresters or air terminals?
4) If they are LAs the they have got a non-linear resister inside meaning they offer a very high impedance for power frequency.
They offer a very low resistance and conduct only if they are subjected to a lightning over voltage. How did you measure and say it is 5 Ohms.

 

[jghrist]

It seems like the OP is confusing lighting air terminals with lightning arresters. Also he is confusing resistance of ground rods with resistance of arresters.

 

[cranky108]

How is this about electrical transmission and distribution?