> This issue, but with coax for CATV between buildings, is probably what
> drove the change to NEC noted above.
Or computer networking/terminals with old coax based ethernet, twinax
(shielded, twisted pair "coax"), etc. There are simply too many systems
that use shielded cables to ignore their impact when looking at
grounding/bonding and power line grounds. Nearly every communications
system ties the shield to chassis effectively connecting it to, and in
parallel with, the power system "safety" ground.
73,
... Joe, W4TV
On 10/19/2017 2:20 PM, 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.
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.
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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