Grounding/Lightning loops?

[Darkstar350]

Does anyone run a circular loop in some excess coax - also known as a grounding or "lightning loop" in their setup?
Ive heard this supposedly helps with grounding/lightning protection

Does it make a noticeable difference? Is it beneficial? Harmful?...

 

[mmckenna]

No. Think about it: Lightning travels thousands of feet through the air. It's not going to stop because of a loop of cable. You are dealing with a huge amount of energy that's trying to find it's way between ground and sky. A few fractions of an inch of cable insulation isn't going to make a difference in a direct strike. I've read some of the justifications for doing this, but I don't necessarily agree with it. I can -kind of- see what some of them are saying about induced energy, but I'm still not agreeing. I've never seen it done at a commercial LMR site, and I've never seen it done at the very few FM broadcast sites I've been at.

Nothing is going to replace industry accepted standards for lightning protection. That means proper grounding, lightning protectors, more grounding, and proper installation. Probably not going to hurt anything to put a loop in the coax if you really want to, but pay attention to how that can act as a choke and don't rely on it for lightning protection.

 

[prcguy]

Make that several miles for lightning travel. When looking very critically at lightning protection, a slight inductance in a ground strap from a tower leg to an otherwise adequate grounding system can seriously degrade the protection to equipment downstream from the tower. The slight inductance can be from a little extra length in the ground strap, or even a sharp bend in a ground lead can cause lightning to arc to something else rather than direct to the ground system under the tower and dissipate.

My company had such a tower in an otherwise well done lightning ground system and we had to have new cad welds done on the tower legs to the buried ground ring when it failed inspection.

So, some inductance in your feedline can alter how lightning reacts to it. Many insulated AM broadcast towers have a spark gap to the ground system and a large inductor between the tower side spark gap and transmitter feed to persuade the lightning into taking the wanted path.

Using some inductance as brought up by the OP would be one of many small considerations in a lightning ground system and by itself probably has no benefit for lightning protection.
prcguy

No. Think about it: Lightning travels thousands of feet through the air. It's not going to stop because of a loop of cable. You are dealing with a huge amount of energy that's trying to find it's way between ground and sky. A few fractions of an inch of cable insulation isn't going to make a difference in a direct strike. I've read some of the justifications for doing this, but I don't necessarily agree with it. I can -kind of- see what some of them are saying about induced energy, but I'm still not agreeing. I've never seen it done at a commercial LMR site, and I've never seen it done at the very few FM broadcast sites I've been at.

Nothing is going to replace industry accepted standards for lightning protection. That means proper grounding, lightning protectors, more grounding, and proper installation. Probably not going to hurt anything to put a loop in the coax if you really want to, but pay attention to how that can act as a choke and don't rely on it for lightning protection.

 

[n5ims]

Those loops are totally useless as a sole method of lightning protection, but may be useful as an additional step when properly installed. The main protection must include providing as direct a path to ground as is possible, generally by using a quality lightning arrestor on the feedline where it enters the transmitter building. This is to prevent as much of the lightning energy from entering the building as possible.

The "lightning loop" on the inside of the building (on the transmitter side of that quality lightning arrestor) may help force that surge back to the arrestor and down to the ground to dissipate. The theory is that the inductance from the loop will act as a choke and keep some of the surge from passing through to the equipment. This choke can't do the full job of a direct strike, but may do some good on the residual amount that bypassed the arrestor, especially on indirect strikes where the surge is much less powerful.

 

[Darkstar350]

It sounds like basically a waste of time - which is what i kind of figured originally...

But - if i do decide to try it out - is it better to make the loop outside of the building or inside? And can this hinder performance at all?

 

[Louwo]

I always thought a loop before going into a house or structure was a place for water on the wires to drip off before entering the home instead of running down the length of the wire.

 

[Rred]

A vertical "drip loop" is just a u-shaped bend of cable. yes, designed so water runs down the loop and would have to run back "uphill" to enter the house, or vehicle.

The OP was talking about a complete CIRCLE of cable for magical inductive purposes.

Totally different animal.

 

[Louwo]

Totally different kind of wire all together. Gotcha ty

 

[kk4bhs]

It sounds like basically a waste of time - which is what i kind of figured originally...

But - if i do decide to try it out - is it better to make the loop outside of the building or inside? And can this hinder performance at all?

won't hurt the performance any at all. As others suggested it might help as a drip loop for water. If you were to do the loop i would do it inside simply because its not outside in the U.V. Yes I know the rest of it is out there but save what you can. It also gives you some extra in case you need to cut off and resolver connectors.