[TowerTalk] Grounding of cables to tower? (N3AE)

[jimlux]

On 10/19/17 11:20 AM, Jim Brown wrote:
> On 10/19/2017 6:49 AM, jimlux wrote:
>> In your case, one could put a 1:1 transformer at the remote building, 
>> primary side fed from the house, secondary side feeding your subpanel, 
>> where neutral and ground would be connected(because it's an entirely 
>> separate system).
>> There would be no "ground path" from house to garage.
> 
> The fly in this ointment, I believe, is that the transformer must be 
> bonded to the ground from the panel that feeds it, so grounds between 
> the two buildings are still tied together. We ran into this issue with 
> audio and video systems in large buildings, where isolation transformers 
> with Faraday shields were used to minimize the transfer of noise from 
> building power to the audio and/or video systems, and misguidedly 
> expected to separate equipment ground for these systems from building 
> ground.

within a building, sure..

> 
> Under current NEC, equipment ground must be carried between buildings. 
> Prior to about ten years ago, NEC permitted a feed between buildings 
> without the equipment ground, with a panel in the second building, 
> neutral bonded to equipment ground, and ground rods for the second 
> building.  Without the transformer but with ground carried between 
> buildings, a panelboard and earth ground are still required in the 
> second building but neutral and ground MUST NOT be bonded in that panel.

Interesting.. I'll have to go look up the history of that change. There 
must have been some problem.

There have been all sorts of issues with grounding/bonding - large 
motors with variable speed drives that have nuisance trips because of 
apparent ground fault, for instance.




> 
>> A 15 kVA "dry transformer" is about $500
>>
>> Of course, if you run your coax, bonded to the tower, bonded to the 
>> garage grounding system, back to the shack in your house, you've now 
>> created a path from "grounding system in the garage" to "grounding 
>> system in house", but that's the only path...
> 
> This issue, but with coax for CATV between buildings, is probably what 
> drove the change to NEC noted above.
> 
> 73, Jim K9YC
> 
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