Cell tower grounding

[rojay]

My company does a lot of cell sites. Grounding scheme is typical on every site- we install a #2 solid ground ring that encircles our equipment platform. All equipment cabinets, h-frames, fence posts, etc are bonded to the ring. The intent of this ring electrode system seems to be to provide a path for a lightning strike.
Would it be appropriate to view this ring as a service grounding electrode?
When we install a new service at a site, I view the ring as a seperate GES and provide 2 ground rods for my service GE and bond them to the ring.
Is this overkill?

 

[ActionDave]

We always tied onto the ground ring, never had a problem with an inspector wanting a ground rod and those rods are doing absolutely nothing.

 

[rojay]

We always tied onto the ground ring, never had a problem with an inspector wanting a ground rod and those rods are doing absolutely nothing.

Yeah, I have to agree with your point on the ground rods. Theyre not really achieving anything that the ground ring hasn't already taken care of.

I suppose the fact that the ring is intended to direct a lightning strike into the earth and away from the equipment doesn't really qualify it as its own seperate 250.106 lightning protection system.

The fact that 99.9% of our construction drawings always call for a seperate, ( illegally unbonded) isolated ground rod for our service equipment got me wondering if they were viewing the ring as some sort of LPS.

 

[ActionDave]

..The fact that 99.9% of our construction drawings always call for a seperate, ( illegally unbonded) isolated ground rod for our service equipment got me wondering if they were viewing the ring as some sort of LPS.

That's weird. Not only is it a code violation I have never seen that on a cell site drawing. Who's the carrier if I may be so bold as to ask?

 

[shortcircuit2]

Yeah, I have to agree with your point on the ground rods. Theyre not really achieving anything that the ground ring hasn't already taken care of.

From my research on this...the perimeter ground-ring protects the structure and is typically placed at 30-inches below finished grade. The ring at 30-inches may not be below the frost line or the permanent moisture level in some parts of the country, or it may not be deep enough for a low-impedance connection to earth depending on the soil resistivity. The added ground rods that are connected to the ring get deeper into the earth for a better low-impedance path for the lightning to dissipate.

The ground rods do achieve something more with regard to lightning protection. Sometimes rods are driven deep (40-60feet) into the earth until a satisfactory low resistance-to-earth is established acceptable to the designing engineer.

This is all over and above what the NEC requires for the Grounding Electrode System. The ground-ring alone qualifies as an electrode with no need for adding rod electrodes.

 

[rojay]

That's weird. Not only is it a code violation I have never seen that on a cell site drawing. Who's the carrier if I may be so bold as to ask?

Rhymes with C- Noble.

 

[tom baker]

By not bonding the separate ground rods to your cell tower ground, there will be difference of potential between the two systems and creates a path into your equipment. The NEC recognizes this and several code cycles ago added intersystem bonding requirements
Please review NEC definition on Intersystem Bond and rules in 250.94 (A)
View your cell tower ground as the intersystem bond, 250.94
Here is a link to Motorola R-56 I consider this the gold standard for telecom grounding
https://sites.auburn.edu/admin/faci...ject Documents/1/Motorola_R56_2005_manual.pdf

 

[ActionDave]

Rhymes with C- Noble.

Noble just started serving my area. I've hooked up a couple generators for them. I've mostly been involved with Horizon and DDT. I thought all of them would just go with the Motorola R66 spec.

My hat's off to you if you do the grounding. We never do because the contractor we work for has his own crew just for that. More cad welds going off than the 4th of July when those guys are working.

 

[brian john]

And if the ground ring is tied to the tower footer you are not going to get any better electrode that the tower concrete footer.

 

[Sahib]

And if the ground ring is tied to the tower footer you are not going to get any better electrode that the tower concrete footer.

Whether it is footer or rod, it helps in easier dissipation of lightning current in association with the earth ring.

 

[brian john]

Whether it is footer or rod, it helps in easier dissipation of lightning current in association with the earth ring.

The tower footers were 10' across and 28 feet in the ground concrete and rebar, if you are attempting to create a good electrode it is hard to beat that.

 

[Sahib]

The tower footers were 10' across and 28 feet in the ground concrete and rebar, if you are attempting to create a good electrode it is hard to beat that.

Yes but if there is any electrical discontinuity in the arrangement due to civil construction lapses, there is a risk of blowing up the tower foundation by a strong lightning current passing through it.

 

[brian john]

Yes but if there is any electrical discontinuity in the arrangement due to civil construction lapses, there is a risk of blowing up the tower foundation by a strong lightning current passing through it.

You can't live your life trying to figure out what others might due to your electrical work once it is completed if I lived by what if, I'd die of an ulcer.

And damage from lighting is always a risk when you rely on a concrete-encased electrode but then the code requires your foundation to be utilized as a concrete-encased electrode. Such is our code.

No matter how you configure it the concrete footer will be grounded, tower bolts are connected to the rebar the tower is bonded at the bottom by an EGC, then there are the coax grounds. Hard to avoid.

Whether the footer is utilized as an electrode or is grounded as noted above lighting will do as it pleases when it hits a tower, it all depends on the location of the strike, magnitude, duration, and the number of strikes.

 

[Sahib]

No matter how you configure it the concrete footer will be grounded, tower bolts are connected to the rebar the tower is bonded at the bottom by an EGC, then there are the coax grounds. Hard to avoid.

In one experimental setup, it was found that absence of binding wires caused separation of rebars in a footing structure and it exploded on passage of test impulse current through it.

 

[brian john]

In one experimental setup, it was found that absence of binding wires caused separation of rebars in a footing structure and it exploded on passage of test impulse current through it.

I have never doubted that, concrete retains moisture which is one benefit the supporters of the "Ufer" electrode promoted. Trees crack due to the rapid expansion of moisture why wouldn't one expect the same of concrete?