Grounding Bonding with Aerial Lashed Fiber

F

FloridaSplash

Member
Location
Central Fl
Occupation
Business Owner
OK all, new to the forum but have always been a MH fan! I run a business that builds Fiber Optic Networks. Most of our work is underground but we stumbled into an pre-existing situation yesterday at the request of a new client that had a recent lightning strike. Its at a ballfield where there are two buildings about 150' apart. One is a concrete structure and the other has a concrete base with a metal upper floor. There is a steel messenger cable installed that supports the fiber cable between the two buildings. One end anchored to the upper level building steel and the other anchored into the concrete building. Client claims they have video of the lightning striking the messenger cable and it wiping out the network switch the fiber was plugged into but the UPS was not affected. This is a stretch in my mind but i have seen some strange things with lightning over the years. The cable is all dielectric, so zero chance of that being related. I would assume the building steel on the one side of the attachment would be bonded. The client is demanding that we place ground rods at both ends of the aerial run and ground the messenger. I am pretty sure that's going to create more issues. Thoughts anyone?
 
OF course thats assuming there is already a legitimate ground, driving two disparate ground rods in addition to the existing could create potential between them. I get its a lightning control issue, if no one else sees this as potentially problematic, ill take that and run. Apparently this has been in place for 6-7 years.. certainly not the first lightning storm in FL
 
FloridaSplash said:
OF course thats assuming there is already a legitimate ground, driving two disparate ground rods in addition to the existing could create potential between them.
Click to expand...
All grounding electrodes including lightning protection must be bonded together for equipotential.
 
FloridaSplash said:
OF course thats assuming there is already a legitimate ground, driving two disparate ground rods in addition to the existing could create potential between them.
Click to expand...
How does grounding the messenger cable change anything other than connecting it to earth? As Roger stated if there are other electrodes they would get connected together.
 
jim dungar said:
This appears to be a lightning 'control' issue. It is not governed by the NEC.
Click to expand...
Overhead communications cables if they have a metallic path back to the utility pole and are attached to a building I think need to be bonded per NEC 800.100 no matter what type, POTS CATV Fiber optic whatever, if it has a metallic path that is bonded at the pole end it needs to be bonded to the grounding electrode system.
UG fiber probably has no metallic messenger.
Communications utilities here have long required their DMARC or as the NEC calls it "Primary Protector" to be within 18" of the electrical service.
 
tortuga said:
Overhead communications cables if they have a metallic path back to the utility pole and are attached to a building I think need to be bonded per NEC 800.100 no matter what type, POTS CATV Fiber optic whatever, if it has a metallic path that is bonded at the pole end it needs to be bonded to the grounding electrode system.
UG fiber probably has no metallic messenger.
Communications utilities here have long required their DMARC or as the NEC calls it "Primary Protector" to be within 18" of the electrical service.
Click to expand...
But.
The OP said the messenger cable ran between two buildings and the fiber was non metallic.
 
jim dungar said:
But.
The OP said the messenger cable ran between two buildings and the fiber was non metallic.
Click to expand...
A bare steel messenger running between two buildings, not part of the 'cable' but I'd still say ground the messenger at both ends, as specified in 770.100 or 800.100. I think utilities put a ground rod every 1400'.

FloridaSplash said:
There is a steel messenger cable installed that supports the fiber cable between the two buildings.
Click to expand...
A bare steel messenger is 'exposed' so it could contact with other electric light or power conductors or a bare utility neutral conductor. I'd look at installing a inter-system ground bar as specified in 250.94.
FloridaSplash said:
The client is demanding that we place ground rods at both ends of the aerial run and ground the messenger. I am pretty sure that's going to create more issues. Thoughts anyone?
Click to expand...

I would not want ground rods at the fiber-optic dmarcs, I'd run all the the non–current-carrying metallic communications 'grounds' to one GES per building. I'd probably run a #6 or #8 bare back to each structures GES.
 
If you run a wire between two separate ground electrodes, then there is a risk that ground currents from nearby lighting strikes will be conducted in through one set of electrodes, through the wire, and out through the other set of electrodes.

This is a serious risk if you have (say) a communications cable (with grounded sheath) running between the two electrodes, or if you have a piece of equipment connected electrically between the two ground electrodes.

But in the OP case, the 'wire' between the two ground electrodes is a steel messenger wire carrying a dielectric optical fiber. I don't see a significant added risk (in this particular case) if this wire is connected between two ground electrodes or ground electrode systems.

If the customer is particularly concerned about lighting striking the messenger wire, then perhaps get it evaluated as an air terminal for a lightning protection system, because intended or not, that is what its being turned into.
 
jim dungar said:
Go ahead, but it is a design decision by you.

The only thing the NEC would care about is the bonding of any ground electrodes.
Click to expand...
The NEC covers grounding of Non–Current-Carrying Metallic Members of Optical Fiber Cables in 770.93 and 770.100
 
jim dungar said:
Is the messenger inside of the fiber cable assembly?
According to the OP the messenger appears to be separate.
Click to expand...
I was responding to your remark that;
jim dungar said:
The only thing the NEC would care about is the bonding of any ground electrodes.
Click to expand...
The NEC also cares about grounding of Non–Current-Carrying Metallic Members of Optical Fiber Cables, I am not sure a 'member' needs to be inside a custom triplex-ed cable assembly to qualify.
 
winnie said:
...

But in the OP case, the 'wire' between the two ground electrodes is a steel messenger wire carrying a dielectric optical fiber. I don't see a significant added risk (in this particular case) if this wire is connected between two ground electrodes or ground electrode systems.

...
Click to expand...

But what would be the benefit of having it grounded at both ends? I don't see any benefit to that, only possible downside. Imo OP's client is just dirt worshipping. I would try to consult an LPS professional for evaluation as you alluded to.
 
You must log in or register to reply here.
Top