Parallel Power Wires for Remote Radio

[kauf connect]

I'm working with a customer who is putting cellular radios up a tower. For long runs from the power source, the AWG8 cable has too much voltage drop. It is -48v DC, 20A. The proposed solution is to run two cables (two conductor, shielded) up to tower. They will not increase the current, just hoping the extra copper gets enough power to the radio. Since the radio only has one bayonet mating, 2 pole power input, we designed a Tee adapter. This seems to be a violation of NEC 310.4, but we have no expert in this area. Our thought was this could be an exception, since a single cable can still handle the current if one of the two is disconnected. Larger conductor size in a single cable is not an option due to the size limits on the 2 pole connector (connector is UL 1977 / IEC 61984 approved). Hoping someone familiar with NEC or NFPA can provide some guidance. Thanks.

 

[qcroanoke]

310.4 (A) exception 1-(a)
They have to be in the same cable.
With it being on the tower would the NEC have any say in it? It is under the control of the communication company.

 

[ActionDave]

With it being on the tower would the NEC have any say in it? It is under the control of the communication company.

That would be my take on it.

 

[winnie]

If I understand your description correctly, your application is similar to but not directly covered by some of the exceptions to the parallel connection rules. For example, if this were a 400Hz AC supply, then you could have multiple small parallel conductors as long as each was individually capable of handling the load current.

As others have noted, the NEC might not even apply....

My take is that if you are already building some sort of adapter box to 'tee' to parallel cables, then you might as well build an adapter box that adjusts to larger cable. Having 1 foot of 8AWG, followed by umpteen feet of 4AWG, followed by 1 foot of 8AWG is a fine way to deal with voltage drop.

-Jon

 

[tom baker]

This is DC power 48 volts and I am not sure the rules on parallel conductors apply.
However the suggest to run larger cable with small at each end seems like a good approach.

 

[Rampage_Rick]

If the limiting factor is the connector at the top of the tower, then you only need to reduce the cable on that end. If the terminals on the bottom of the tower accept 4ga wire there's no real need to splice in a foot of 8ga there.

 

[GeorgeB]

If the limiting factor is the connector at the top of the tower, then you only need to reduce the cable on that end. If the terminals on the bottom of the tower accept 4ga wire there's no real need to splice in a foot of 8ga there.

Conceptually, we do the equivalent thing in proportional valve power regularly ... I'll run #12 or #10 for 0V and +24 to a jbox near the valve with another (can be #24 from ELECTRICAL criteria, but most prefer #16 for mechanical reasons) shielded for analog, then a multiconductor #18 several feet from the jbox to the valve connector.

When the run gets that long, my industry often finds it economical to run 120 or 240 to the jbox, and have a switching power supply there ... fwiw.

 

[petersonra]

run a 1/0 and splice smaller conductors at both ends.

if you want even less VD run several 1/0's in parallel.

 

[GoldDigger]

...if you can get 1/0 two wire with suitable shielding and make the splice in a way that preserves the shielding.

Sent from my XT1080 using Tapatalk

 

[petersonra]

...if you can get 1/0 two wire with suitable shielding and make the splice in a way that preserves the shielding.

Sent from my XT1080 using Tapatalk

Run THHN in rigid. That is about as good of a shield as it gets.

If you have to have parallel conductors and you have to meet NEC rules, at some point your options get kind of limited as to what you can do.

Personally, I am not sure why the OP is involved in seeking a solution. It seems like something the engineer who designed the site ought to be handling. I am not sure why a salesmen is asking the question. Being the eternal cynic I suspect the engineer gave the salesman the right answer but he thinks it is too expensive and is out searching for a cheap answer. But, that is just me.

 

[iwire]

With it being on the tower would the NEC have any say in it? It is under the control of the communication company.

That would be my take on it.

Unless the tower is under the exclusive control of a utility I don't see it being outside the NEC.

(B) Not Covered. This Code does not cover the following:

(4) Installations of communications equipment under the
exclusive control of communications utilities located
outdoors or in building spaces used exclusively for
such installation

 

[ActionDave]

Unless the tower is under the exclusive control of a utility I don't see it being outside the NEC.

I have nothing to go on but my own experience at cell sites.
I don't do tower work, just work in the shelters, but I know inspectors in the three states I have worked in have never inspected anything on the towers. So either there is not anything under the NEC to inspect on the towers, or they don't know there is something there they are supposed to inspect. Either way the towers don't get inspected. Actually nothing gets inspected after the service to the shelter.

That is not exactly true. Everything gets looked at by a cell company engineer. Some of those guys are a special breed for sure.

 

[ceb58]

I have nothing to go on but my own experience at cell sites.
I don't do tower work, just work in the shelters, but I know inspectors in the three states I have worked in have never inspected anything on the towers. So either there is not anything under the NEC to inspect on the towers, or they don't know there is something there they are supposed to inspect. Either way the towers don't get inspected. Actually nothing gets inspected after the service to the shelter.

That is not exactly true. Everything gets looked at by a cell company engineer. Some of those guys are a special breed for sure.

I agree with what you are saying except when our towers are built the State Elect. Inspector checks the grounding ring, and the service on the building. Every thing after the inside service disconnect is inspected in the factory and is stamped by a third party inspection company. However, we will not allow anyone to run any type power cable on the tower, with the exception of the tower light cable.

 

[kauf connect]

Thanks

Thanks

Thanks to all for your input. Since the customer manufactures the radio unit I thought the engineer we're dealing with should have had more insight into this subject. One of our engineers visited the customer about a week ago and saw the application out in the parking lot. This is a 4G upgrade for one of the US Operators. We'll be talking with the customer later this week and I plan to have him clarify some of the points made in this forum.

 

[dereckbc]

Thanks to all for your input. Since the customer manufactures the radio unit I thought the engineer we're dealing with should have had more insight into this subject. One of our engineers visited the customer about a week ago and saw the application out in the parking lot. This is a 4G upgrade for one of the US Operators. We'll be talking with the customer later this week and I plan to have him clarify some of the points made in this forum.

Something very strange going on here. I do a lot of this kind of work and work with all the manufactures of cellular radio equipment like ALU, Motorola, and Erricson. We do a lot of tower top radios and all that power is on the 12 runs of coax going up to Tower Top Mounted Amplifiers and integrated in the radio equipment all provided by the manufacture. NEC has no say what so ever about it. I must be missing something.

 

[Rampage_Rick]

One of our two major GSM networks has standardized with Huawei. It's a pretty clean and foolproof system from what I've seen. For towers and tall buildings they run a ground, a multi-conductor DC cable (I've seen up to 24 conductor 8-ga) and a multimode fiber (24 count)
Everything goes into a 18x24 Hoffman enclosure on the top side, which acts as a breakout box to feed each of the RRUs. Every cable topside is color-coded according to the standard label inside the enclosure.