Bonding a network radio

Status
Not open for further replies.
G

greenspark1

Senior Member
Location
New England
Hello,
I have a Cisco 1552 wireless radio being installed at a medium sized commercial existing building. We're running RMC up the exterior to the 6' radio mast with CAT6 and fiber inside. After reading 810.21 it appears we require a bonding conductor. I have never seen these used before for exterior antennas so want to make sure I understand correctly:
I need to run the wire from the radio back down the building to either the intersystem bonding termination or building grounding electrode system.
I can strap it to the outside of the conduit
I cannot use the conduit to accomplish this bonding
I cannot bond to the existing lightning system

Please let me know if I have my wires crossed, this is looking complicated. Thanks!
 
Sounds like you're right.

Think of this like a DirecTV dish - needs a ground wire running back to the intersystem grounding bar.
The Cisco installation manual that comes with the radio should have more details, such as what wire size to use (6 AWG)
http://www.cisco.com/c/en/us/td/docs/wireless/access_point/1550/installation/guide/1550hig.pdf


I'd also add in there that you may want to get lightning protectors to put between the radios and the antennas. Your Cisco dealer should be able to tell you if they're needed/recommended for your installation and if so, which ones to get.
Similar to http://www.l-com.com/surge-protector-n-male-to-n-female-bulkhead-0-6-ghz-90v-lightning-protector
 
Thanks for the response! I haven't had Dish before so am not familiar with it. They run a #6 all the way back to the house?

I did look at that 1550HIG but those diagrams are so simplistic and make it look easy. With a large existing building it is no easy feat to run a dedicated bonding jumper back to the grounding system. Bonding to the building's lightning system would be so much simpler.

Lightning/surge protection is definitely a good idea. I'm not sure how to do it with a 1552 though since the antennas screw straight into the radio. I'm used to using them for externally mounted antennas.
 
If the antennas are local to the radio, I do not see a particular need for lightning protection on them. Any induced voltage at that location will already be inside the unshielded case anyway.
But if Cisco offers remote mounting kits for external antenna or just cable input as an option, then you have a place to insert the spark gaps or other protection.
 
Here's an interesting one- can I bond the radio to an existing lighting protection system to meet 810.21? The LPS is bonded to the building's grounding electrode system. The LPS is also much closer than the GES so will provide a better & lower impedance path than running a separate bonding wire all the way down a building to the GES.

Using the LPS seems like a better solution for antenna static and lightning protection than running a separate bonding conductor to the GES. Thoughts?
 
bonding

bonding

greenspark1 said:
Here's an interesting one- can I bond the radio to an existing lighting protection system to meet 810.21? The LPS is bonded to the building's grounding electrode system. The LPS is also much closer than the GES so will provide a better & lower impedance path than running a separate bonding wire all the way down a building to the GES.

Using the LPS seems like a better solution for antenna static and lightning protection than running a separate bonding conductor to the GES. Thoughts?
Click to expand...

If you bond the radio to the existing lightning protection system in between the topside and earthed conductors, you will create a parallel path through the grounding pin (EGC) on your equipment. This is not recommended.

Think Kirchoff...
 
Last edited:
cuba_pete said:
If you bond the radio to the existing lightning protection system in between the topside and earthed conductors, you will create a parallel path through the grounding pin (EGC) on your equipment. This is not recommended.

Think Kirchoff...
Click to expand...

Well a separate bonding conductor to the building grounding system will also create a parallel path. The EGC will go through a number of panels before hitting the buildings ground. I don't see how bonding to the lightning system is any worse than a conductor to the building ground.

Parallel neutrals is clearly a bad thing, but not sure why having parallel grounds would cause any problems. It will only be used for static, lightning discharge, or other anomalous events.

I'll do some reading on the R56, thanks for the idea.
 
Think Kirchoff

Think Kirchoff

A dedicated lightning protection system should not be used as an EGC because the path for the discharge would now be going through equipment and devices instead of directly to it's dedicated ground rod. My problem is not the electrical nature using the LPS as an EGC bond...assuming, of course, that the LPS is bonded to the building grounding grid (as per 250.106). If the LPS is not bonded then the EGC is not bonded, and not to code.

My problem is that the system is even more of a danger now that LPS conductors have been brought into a structure (via the equipment power and data wiring). You would have spark gaps internal to the equipment which would find their way onto the energized conductors of the equipment.

I don't like assumptions, so I would install the antenna EGC to the code and not rely on on an LPS ground.

Proper installation would reference NFPA 70 and NFPA 780 to start.
 
Last edited:
cuba_pete said:
A dedicated lightning protection system should not be used as an EGC because the path for the discharge would now be going through equipment and devices instead of directly to it's dedicated ground rod. My problem is not the electrical nature using the LPS as an EGC bond...assuming, of course, that the LPS is bonded to the building grounding grid (as per 250.106). If the LPS is not bonded then the EGC is not bonded, and not to code.

My problem is that the system is even more of a danger now that LPS conductors have been brought into a structure (via the equipment power and data wiring). You would have spark gaps internal to the equipment which would find their way onto the energized conductors of the equipment.

I don't like assumptions, so I would install the antenna EGC to the code and not rely on on an LPS ground.

Proper installation would reference NFPA 70 and NFPA 780 to start.
Click to expand...

Yes, I am asking the question because I don't see it covered by NFPA 70.

This isn't an EGC, it's a bonding conductor per 810.21. I was saying an EGC to the antenna has a longer and less direct path to the building grounding system than the lightning protection system.

It is an exterior antenna so the ground isn't brought into the building. Roof mounted equipment is REQUIRED to be bonded to the lightning protection system, the question is if it also needs a separate bonding conductor down to the building grounding system.

Motorola's R56 specifically allows the lightning system to be used INSTEAD of running a separate bonding conductor to the building ground:

Motorola R56 capture.JPG
 
EGC

EGC

greenspark1 said:
It is an exterior antenna so the ground isn't brought into the building.
Click to expand...

How does the equipment get power...from within the facility? Flashover distances should be calculated if power is outside.

Roof mounted equipment is REQUIRED to be bonded to the lightning protection system, the question is if it also needs a separate bonding conductor down to the building grounding system. Motorola's R56 specifically allows the lightning system to be used INSTEAD of running a separate bonding conductor to the building ground.
Click to expand...

If you have specific guidance from the manufacurer then I would go with that.

In addition, there should be some mention of how you will be routing the communication cable from the equipment into the facility. That is another part of what I was referring to, as well as how you are getting power to the equipment. Unless the communication line if fiber, then you are potentially routing a lightning surge into the building. SPD's should be used in concert with the equipment, and hopefully your manual gives proper guidance on that as well.
 
Status
Not open for further replies.
Top