CATV Grounding question

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Old 05-11-14, 04:52 AM
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CATV Grounding question

Our CATV comes overhead. I understand that the cable company grounds the coax up at the poco transformer.

So if that is the case, is a ground block in the demarcation box on the side of the house (connected to the grounding electrode) necessary?
 
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Old 05-11-14, 05:23 AM
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I'd install an intersytem grounding bridge.
 
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Old 05-11-14, 05:32 AM
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I should mention I know the requirments in the new code for ISB or otherwise having all phones, tv etc grounded to the GEC. However, isn't that redundant in the case of the cable coax since its grounded at the transformer?
 
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Old 05-11-14, 05:44 AM
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I haven't done cable power supplies in many years, but they were never grounded at the transformer. They used a ground rod.
 
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Old 05-11-14, 11:31 AM
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However, isn't that redundant in the case of the cable coax since its grounded at the transformer?
Technically everything connected to the pole shares a common ground but the cable line is not directly connected to the transformer and MUST be grounded at the house end.
 
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Old 05-12-14, 06:39 AM
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Technically everything connected to the pole shares a common ground but the cable line is not directly connected to the transformer and MUST be grounded at the house end.
I would agree with that 100%. I doubt any power company would allow a cable TV company to attach anything to their equipment or lines on a pole.
 
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Old 05-12-14, 10:46 AM
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Inter-system bonding isn't new to the NEC. Quick research shows it in the 2008 NEC (and I believe well before that too).

There are a few reasons for it. One is that it provides a level of redundancy. If there's a break in the coax shield or the neutral triplex coming from the pole, it ensures equipment grounds are always at the same potential even if something breaks.

I understand it also has to do with relatively high resistivity at very high (lightning) voltages. The 200' cable drop from the pole may have a few ohms of resistance. At tens of thousands of volts, that can mean a significant difference in potential at an appliance like your TV.

It's the same reason that any pole with equipment on it is grounded. Sure, the ground from 3 poles over should work the same... but the system is built with safety and reliability in mind.
 
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