Ground ring as effective fault current path

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hhsting

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Glen bunie, md, us
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I have monopole cell tower which is bonded thru grounding electrode conductor thru ground ring. I also have DC conductors going up the tower to antennas, RRUs, radios etc.

DC conductors metal sheath, antennas, RRUs are all have bonding jumper to ground bus. The ground bus then has grounding electrode conductor to ground ring. Also all the DC cabinets on floor panels have grounding electrode conductor on enclosure to ground ring.

Let’s say one of the DC conductors going up tower to antenna breaks and touches the tower. DC conductors do not have equipment grounding conductor for antennas, RRUs as far as I know. Anyone can here correct me if I am incorrect please. So when someone touch the tower fault current would go thru tower grounding electrode conductor to ground ring to any one of one of the enclosure back to the system.

Would that not be like using earth as return path?
 
It sounds like a typical ungrounded system: the first fault would establish an accidental bond; the second one a fault.
 
hhsting said:
I have monopole cell tower which is bonded thru grounding electrode conductor thru ground ring. I also have DC conductors going up the tower to antennas, RRUs, radios etc.

DC conductors metal sheath, antennas, RRUs are all have bonding jumper to ground bus. The ground bus then has grounding electrode conductor to ground ring. Also all the DC cabinets on floor panels have grounding electrode conductor on enclosure to ground ring.
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The only grounding electrode conductor is from the service neutral to the grounding electrode. Everything you are mentioning here are bonding jumpers.
...Would that not be like using earth as return path?
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Why would you think this? Where, when and how is the earth being used as a return path when every piece of metal on the site is bonded to every other piece of metal and all of that is brought back to one central place with all of the before mentioned bonding jumpers?
 
ActionDave said:
The only grounding electrode conductor is from the service neutral to the grounding electrode. Everything you are mentioning here are bonding jumpers.
Why would you think this? Where, when and how is the earth being used as a return path when every piece of metal on the site is bonded to every other piece of metal and all of that is brought back to one central place with all of the before mentioned bonding jumpers?
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Well everything is bonded or have grounding electrode to ground ring. The ground ring is buried in earth. Would not the ground ring resistance change due to buried?
 
tom baker said:
Who owns the cell tower, private/gov't or telecom carrier (like verizon)?
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I don’t know who own existing cell tower but it’s Not on federal lands and AHJ apply to land where cell tower is. I know the equipment on cell tower and on ground belongs various telecom carriers
 
hhsting said:
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Let’s say one of the DC conductors going up tower to antenna breaks and touches the tower. DC conductors do not have equipment grounding conductor for antennas, RRUs as far as I know. Anyone can here correct me if I am incorrect please. So when someone touch the tower fault current would go thru tower grounding electrode conductor to ground ring to any one of one of the enclosure back to the system.
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No. Someone touching the tower does not complete a circuit. You've described all the metal as being bonded together and earthed, so there should be no meaningful difference in potential between any of it and the earth. There would be no fault current unless the person is also touching the other DC conductor. Or unless the DC system is grounded, which you didn't say, in which case the fault current would flow through the metal before anyone touched it.

Would that not be like using earth as return path?
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No. You haven't described another electrode anywhere in the system. You can't have earth current in a system with one electrode.
 
jaggedben said:
No. Someone touching the tower does not complete a circuit. You've described all the metal as being bonded together and earthed, so there should be no meaningful difference in potential between any of it and the earth. There would be no fault current unless the person is also touching the other DC conductor. Or unless the DC system is grounded, which you didn't say, in which case the fault current would flow through the metal before anyone touched it.



No. You haven't described another electrode anywhere in the system. You can't have earth current in a system with one electrode.
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Cell tower sites has incoming AC electric utility service which is grounded. The AC system goes to the cabinet which has rectifiers and DC battery which then feed the cable conductors to the tower. The metal sheath of DC conductor is also bonded to ground ring.

I am not sure if DC system is grounded or not but enclosure do have grounding electrode conductor going to the grounding ring.
 
hhsting said:
Cell tower sites has incoming AC electric utility service which is grounded. The AC system goes to the cabinet which has rectifiers and DC battery which then feed the cable conductors.

I am not sure if DC system is grounded or not but enclosure do have grounding electrode conductor going to the grounding ring.
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Okay. We need to know if there are equipment grounding conductors from the service to the cabinet to the tower, that bond the tower. There should be. That is required and arguably 100 times more important than the ground ring.
 
jaggedben said:
Okay. We need to know if there are equipment grounding conductors from the service to the cabinet to the tower, that bond the tower. There should be. That is required and arguably 100 times more important than the ground ring.
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Right their is EGC from AC service to service equipment to AC panelboard to AC panelboard feeder breaker which feed cabinet and rectifier. From cabinet which houses rectifier DC side to ground level equipment to cables up tower please see this post. Not sure if there is any. Anyone here know if there are any?:

Cell tower cable running up have equipment grounding conductor

I have monopole cell tower. The tower has DC conductor cables that run from equipment on ground to cell tower antennas, RRUs, etc up top. Kind of like this: https://wirelessestimator.com/wifi/images/uploads/Guying%20Monopole.jpg Does anyone here know do those DC conductor cables that run up...
forums.mikeholt.com
 
hhsting said:
Right their is EGC from AC service to service equipment to AC panelboard to AC panelboard feeder breaker which feed cabinet and rectifier. From rectifier DC side to ground level equipment to cables up tower please see this post. Not sure if there is any. Anyone here know if there are any?:
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There needs to be an equipment grounding conductor run with the AC and DC circuits wherever they go. That's basic NEC. 250.110

I thought you were telling us what was in the plans or installation. Tell whoever is proposing it they need an EGC. If there isn't an EGC, and the DC conductors are referenced to ground (which they would be if just rectified from AC without an isolation transformer), then that would be using the earth as a ground fault return path and would be a violation. If the DC is ungrounded and isolated it wouldn't be a return path, but it doesn't matter. The EGC is required. Period.
 
jaggedben said:
There needs to be an equipment grounding conductor run with the AC and DC circuits wherever they go. That's basic NEC. 250.110

I thought you were telling us what was in the plans or installation. Tell whoever is proposing it they need an EGC. If there isn't an EGC, and the DC conductors are referenced to ground (which they would be if just rectified from AC without an isolation transformer), then that would be using the earth as a ground fault return path and would be a violation. If the DC is ungrounded and isolated it wouldn't be a return path, but it doesn't matter. The EGC is required. Period.
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That’s what I am trying to figure out. If the I have cell tower similar to shown below link with antennas, RRUs equipment and DC conductor cables that run up the tower and feed it do they need EGC or not? In my plans I have never seen any consulting putting EGC DC side only AC side. Consultants only show bonding jumper from metallic DC conductor sheath, metallic enclosure, mast, antennas, radio enclosure to ground bus bar which then bonds to ground ring. Are they not mostly communication cables? Now I am told there are also power cable DC shielded cable for 5G as well post link #12


 
hhsting said:
That’s what I am trying to figure out. These are DC 45V. If the I have cell tower similar to shown below link with antennas, RRUs equipment and DC conductor cables that run up the tower and feed it do they need EGC or not? In my plans I have never seen any consulting putting EGC DC side only AC side. Consultants only show bonding jumper from metallic DC conductor sheath, metallic enclosure, mast, antennas, radio enclosure to ground bus bar which then bonds to ground ring. Are they not mostly communication cables? Now I am told there are also power cable DC shielded cable for 5G as well post link #12


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Previous post edited to add these are about 60 to 45VDC
 
jaggedben said:
There needs to be an equipment grounding conductor run with the AC and DC circuits wherever they go. That's basic NEC. 250.110

I thought you were telling us what was in the plans or installation. Tell whoever is proposing it they need an EGC. If there isn't an EGC, and the DC conductors are referenced to ground (which they would be if just rectified from AC without an isolation transformer), then that would be using the earth as a ground fault return path and would be a violation. If the DC is ungrounded and isolated it wouldn't be a return path, but it doesn't matter. The EGC is required. Period.
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However to answer the above post I think the negative terminal of 48VDC conductor part of hybrid cable power is grounded going to ground ring in cabinet and have single pole DC breakers in cabinet. Each hybrid cable power negative does go to antenna, RRUs negative terminal however the negative hybrid cable power is not bonded to the metallic tower.

Instead I have bonding jumper from antenna enclosure, mast, hybrid cable metallic sheath to ground bar which then bonds to ground ring. The tower has bonding jumper to grounding ring. Please see post #16 link page 18 showing grounding config of everything.

If the hybrid cable going to RRUs, antennas, insulation breaks touches the tower then would not then that config be using ground earth as ground fault return path or not?
 
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hhsting said:
If the hybrid cable going to RRUs, antennas, insulation breaks touches the tower then would not then that config be using ground earth as ground fault return path or not?
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I think the fact that everything is bonded all the way back to main grounding bar takes care of any possible fault current on the DC conductors and serves as an EGC. At any rate it is not using the earth as a ground fault return path. The earth is not used as a conductor in this case any more than it is in any other properly wired installation with two structures.
 
As long as there is some type of bonding jumper between the location of the DC source (cabinet?) and the tower everything should be fine.
 
hhsting said:
However to answer the above post I think the negative terminal of 48VDC conductor part of hybrid cable power is grounded going to ground ring in cabinet and have single pole DC breakers in cabinet. Each hybrid cable power negative does go to antenna, RRUs negative terminal however the negative hybrid cable power is not bonded to the metallic tower.
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Not that it matters for this discussion, but the positive 48VDC "return" conductor would be grounded and the hot lead would be -48VDC.
That being said, I've seen documents describing floating DC feeds to RRUs that have separate surge/lighting protection devices on the positive and negative conductors. So it might be wise to confirm that the +48VDC return conductor is bonded to the cabinet ground bar in your situation.
 
jaggedben said:
As long as there is some type of bonding jumper between the location of the DC source (cabinet?) and the tower everything should be fine.
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There is no shortage of bonding jumpers on cell sites.
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