cell tower dc bonding jumper sizes

[hhsting]

I have cell tower which requires plan review permit as they are adding new antenna equipment, RRHs on it.

Please assume cell tower is under NEC.

Please also note that the cell tower equipments up top is fed from rectifier at cabinets bottom of tower which converts AC to DC. The system voltage of the equipment on cell tower is 48vdc, 2 wires.

Attached sketch shows one sector of cell tower that has antennas and RRHs casings bonded to the sector ground bus bar on tower using wire bonding jumpers. The ground bus then has grounding electrode conductor from ground bus bar to grounding electrode ground ring

I am having hard time finding how to size the bonding jumpers in the attached sketch labeled B1 that bond from cell tower equipments metallic casings to sector ground bus bar using NEC 2014 for 48VDC system? I looked in NEC 2014 section 250 part VIII but I was not able to find how to size for DC systems bonding jumper. Can anyone please help?. Especially for cell tower

 

[LarryFine]

I believe the sizing for DC is the same as for AC, and dependent on the circuit or conductors feeding each antenna.

The site engineer (I mean the cell site, not necessarily the job site) should have this information already determined.

Added: Also, lightning protection is part of the equation.

 

[hhsting]

I believe the sizing for DC is the same as for AC, and dependent on the circuit or conductors feeding each antenna.

NEC 2014 part VIII of section 250.160 says direct current systems shall comply with part VIII and other sections of Article 250 not specifically intended for ac systems.

So I take it NEC is saying part VIII apply to dc systems and dc systems also comply with 250 that are NOT specifically for AC systems.

Based on that I dont follow how you can say DC size same as AC system

 

[LarryFine]

Based on that I dont follow how you can say DC size same as AC system

"
Only because I haven't read it. As "Ahnold" would say, "Ah'll be bahk!"

"Ah'm bahk!"

From what I see, 250.166 and 250.168 apply.

 

[hhsting]

"
Only because I haven't read it. As "Ahnold" would say, "Ah'll be bahk!"

"Ah'm bahk!"

From what I see, 250.166 and 250.168 apply.

250.166 is about grounding electrode conductor DC systems. Post #1 attachment conductors label B1 go from cell tower equipment casing to sector ground bus bar. According to definition of grounding electrode conductor section 100 the B1 conductor post #1 does not fit definition GEC.

250.168 is about DC systems bonding jumper at the source or at first disconnecting means which bond equipment grounding conductors to grounded conductor. Post #1 conductors in question B1 are not in first disco or at the source and does not bond equipment grounding conductors to grounded conductor. Post #1 attachment B1 go from equipment casings up top cell tower to ground sector bus bar up tower.


I don’t see how both 250.166, 250.168 apply either as well so how can you say they apply?

 

[JGinIndy]

Just a question. Did the design Engineering size the bonding and you are just verifying or are you having to design?

 

[LarryFine]

I don’t see how both 250.166, 250.168 apply either as well so how can you say they apply?

Your turn. You tell me which article it's in, and I'll be glad to read it.

 

[hhsting]

Just a question. Did the design Engineering size the bonding and you are just verifying or are you having to design?

I am plans reviewer. The design engineer on plans did not provide size of B1 conductors post #1 and they are new. Send plans back saying provide cable size based on NEC 2014 Section 250 and now I am being challenge as to how to size B1 conductors post #1 attachment based on NEC 2014.

 

[hhsting]

Your turn. You tell me which article it's in, and I'll be glad to read it.

If I knew I wouldn’t post the question. I don’t know so I am asking on most knowledgeable forum with most knowledgeable people about NEC. I just did some research before posting and I had no luck maybe someone here knows and can help

 

[JGinIndy]

I am plans reviewer. The design engineer on plans did not provide size of B1 conductors post #1 and they are new. Send plans back saying provide cable size based on NEC 2014 Section 250 and now I am being challenge as to how to size B1 conductors post #1 attachment based on NEC 2014.

Well I do plan review as well and if the design firm leaves out a detail such as this I simply send out an RFI back to design. Hey just trying to help. Also, in all my years I have never had a set of plans for a cell tower. When in doubt go big call it 3/0 cu

 

[LarryFine]

You can't go wrong if they match the circuit conductors.

 

[hhsting]

You can't go wrong if they match the circuit conductors.

where does it say that in NEC 2014?

 

[Fred B]

Try Article 810, NYC codes recognizes this article to relate to cellular service antenna towers. Specifically Article 810.15 reference article 810.21(A) - (K) Bonding Conductors and Grounding and ANSI t1.334-2002

Also an ATT document states:
1.4 Grounding Requirements
A grounding system that covers the tower, structure, and site must be provided to insure the
dispersal of lightning and foreign voltages. The grounding system should include grounding
electrodes (rods), a ground ring(s), radial (counterpoise) conductors, either individually or in
combination. To provide the best possible protection, a combination of all items should be
used. Actual design should be determined based on lightning exposure, soil resistivity, as
well as location and design of site.
It is recommended that the ground system meets the following minimum requirements:
Metallic ground rods that are 8’ x 5/8”.
A ground ring that is composed of a minimum of #2 AWG bare copper conductor.
The ground ring is to be buried a minimum of 30” below final grade.
Each part is bonded using either an exothermic weld or irreversible connector.
The attachment to the grounding system or tower/structure ring ground must be via #6 AWG
or larger insulated copper ground wire provided by either the cell site contact or the AT&T
engineer. In either case, the ground wire should be protected from damage and, in some
cases, this may require owner/tenant-provided conduit. (Ground bar specifications will be
based on the forecasted number of circuits, etc.) If a pedestal-type terminal is used for
entrance cable protection, the AT&T engineer will request that the owner/tenant provide a #6
ground wire and coil sufficient slack wire in the vicinity of the proposed pedestal location. If
the protectors will be located inside a building at the site, normal design procedures for in-
building terminations protectors should be followed.
All local building codes are to be followed as well as the specifications listed in the NFPA
70: National Electric Code, Article 250 – Grounding and Bonding and ANSI T1.334-2002,
"Electrical Protection of Communications Towers and Associated Structures", and any other
applicable standards.

Tried to capture link but didn't work, but was from results of the ANSI search.

 

[JGinIndy]

Hey Fred, yes I got to looking around last night “ inquiring minds “ and ran across that. Also, NFPA 76 and obviously NFPA 780 for LPS as well. NEC 810 in a round about way sure seems to be the go to Article.

 

[hhsting]

Try Article 810, NYC codes recognizes this article to relate to cellular service antenna towers. Specifically Article 810.15 reference article 810.21(A) - (K) Bonding Conductors and Grounding and ANSI t1.334-2002

Also an ATT document states:
1.4 Grounding Requirements
A grounding system that covers the tower, structure, and site must be provided to insure the
dispersal of lightning and foreign voltages. The grounding system should include grounding
electrodes (rods), a ground ring(s), radial (counterpoise) conductors, either individually or in
combination. To provide the best possible protection, a combination of all items should be
used. Actual design should be determined based on lightning exposure, soil resistivity, as
well as location and design of site.
It is recommended that the ground system meets the following minimum requirements:
Metallic ground rods that are 8’ x 5/8”.
A ground ring that is composed of a minimum of #2 AWG bare copper conductor.
The ground ring is to be buried a minimum of 30” below final grade.
Each part is bonded using either an exothermic weld or irreversible connector.
The attachment to the grounding system or tower/structure ring ground must be via #6 AWG
or larger insulated copper ground wire provided by either the cell site contact or the AT&T
engineer. In either case, the ground wire should be protected from damage and, in some
cases, this may require owner/tenant-provided conduit. (Ground bar specifications will be
based on the forecasted number of circuits, etc.) If a pedestal-type terminal is used for
entrance cable protection, the AT&T engineer will request that the owner/tenant provide a #6
ground wire and coil sufficient slack wire in the vicinity of the proposed pedestal location. If
the protectors will be located inside a building at the site, normal design procedures for in-
building terminations protectors should be followed.
All local building codes are to be followed as well as the specifications listed in the NFPA
70: National Electric Code, Article 250 – Grounding and Bonding and ANSI T1.334-2002,
"Electrical Protection of Communications Towers and Associated Structures", and any other
applicable standards.

Tried to capture link but didn't work, but was from results of the ANSI search.

NEC 2014 section 810.15 does not reference ANSI t1.334-2002. The cell tower is monopole. Has AT&T antennas and radios on it. Typically what I see is minimum of #6 awg from antenna or RRH casing to the ground bus bar. However NEC 2014 Section 810.21(H) says min of #10 awg. Also no mention of sector ground bus bar. I don’t understand?

I just cant seem to find minimum of #6 awg in NEC 2014 for bonding conductors from antenna or RRH to sector ground bus bar. Do you know where would #6 awg minimum come from for post #1 conductors label B1 from antenna or RRH to sector ground bus bar?

 

[augie47]

Does anyone in your organization actually concern themselves with this ??
I've seen a hundred +- cell towers inspected and the farthest I've ever seen an inspector look was the termination of the feeder.
The site engineers normally verify the grounding.

 

[Fred B]

NEC 2014 section 810.15 does not reference ANSI t1.334-2002. The cell tower is monopole. Has AT&T antennas and radios on it. Typically what I see is minimum of #6 awg from antenna or RRH casing to the ground bus bar. However NEC 2014 Section 810.21(H) says min of #10 awg. Also no mention of sector ground bus bar. I don’t understand?

I just cant seem to find minimum of #6 awg in NEC 2014 for bonding conductors from antenna or RRH to sector ground bus bar. Do you know where would #6 awg minimum come from for post #1 conductors label B1 from antenna or RRH to sector ground bus bar?

ANSI reference was from the NYC codes as well as the AT&T documents. Some references state that the cell phone tower is a utility service and not covered by NEC70 but will reference that in their construction documents provided to FCC when permitting for a new or refurbished tower or service. Thus if it is referenced it becomes part of the listing requirement even though technically not covered by the specific code that was referenced.
This is true in other applications like manufactured homes, under HUD controls but may reference specific portions of NEC and then become enforceable.
AFA a #6 minimum being listed, in general a mfg or in this case the utility provider can request a minimum above what is required by the NEC code and it is still compliant, anything less is violation. #6 is larger than #10 thus still compliant.
This reference is a specific AT&T document and under their criteria AT&T is requesting a #6 and thus become part of their requirements to be compliant and thus enforceable.
This figure may be in the ANSI section but don't know, don't have that code.
Edit: And what @augie47 said.

 

[hhsting]

What feeder? The AC feeder to the rectifier AC, feeder to DC side to the antenna? If cell tower is under NEC and plans don’t state it is Not under NEC and NEC 2014 section 810 cover the bonding jumper size I don’t see how inspectors just stop at feeder.

 

[Greentagger]

Why not use your authority as a plan reviewer and ask the designer what is intent is?

 

[don_resqcapt19]

I would not even take a second glance at the grounding and bonding design for an engineered cell tower. That is a very specific installation and the designers know what is needed to make the system work correctly.
I might look at the service and the normal electrical equipment, but beyond that, I am leaving that all up to the cell company's engineers.