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I'm at a loss here. So Everytime I plug the Ethernet cable into my computer from the modem the DVR shorts out. Had the cable company out here and he said there's a lot of current on my coax. We disconnected the computer and still a lot of current on the line. He checked the voltage coming off the TV and it was pegging the needle. We changed plug and it dropped to 20 v. No voltage feedback off the computer. Tried it after changing plugs and as soon as I plug the Ethernet cable in boom box goes out. With the TV computer off the coax the power is still on the return line he said. I'm not technically savvy so I can use suggestions on this. Is it electrical could it be the modem? The cable is grounded to the metal pipe coming out of the electric meter. Any help would be greatly appreciated.

closed as off-topic by isherwood, Daniel Griscom, Machavity, Tyson, Retired Master Electrician Nov 24 '18 at 21:59

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  • Sorry, but electronics troubleshooting doesn't fall under "home improvement" as this site defines it. – isherwood Nov 15 '18 at 16:05
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    @isherwood The one part that may be for this site is the question of "electrical" - e.g., if things are really messed up and ending up with a ground loop or something like that. – manassehkatz Nov 15 '18 at 16:31
  • That occurred to me, but we don't have much to work with here in that arena. Doug, you could revise to ask about troubleshooting voltage on your coax line instead of mixing in all the device issues. – isherwood Nov 15 '18 at 16:38
  • Are you new to this house? Did the prior owner have satellite dish? 20v sounds strangly like an 18v powered splitter/amplifier for directv is still wired in. – Tyson Nov 15 '18 at 17:14
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    The question may be framed as "electronics troubleshooting" but the real question is why the house's grounding system isn't actively preventing this from happening. – Harper Nov 15 '18 at 17:32
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It's worse than that. Aside from the fact that all that current down your cable is spinning your electric meter and wasting money, there's also the life-safety problem that something is floating your grounds to potentially hazardous voltages. You could get a shock off anything grounded. Which is the opposite of how grounds are supposed to work!

Grounding Electrode System

A house that floats has a problem with its grounding electrode system. This is what connects your house "ground" to actual earth. Go over that system with a fine tooth comb -- but watch it - it's energized!

If you find it is energized and flowing current, try turning off breakers in groups until you narrow down which breaker must be on for that condition to occur. Once I had that problem and did that test before I fixed it: it uncovered a second problem, a circuit with a ground fault.

The neutral-ground bond

It's also worth checking your neutral-ground bond in your main panel only. Sometimes these burn out, especially when they are simply a green #10 screw going from neutral bar to panel: the screw head may look fine but behind, the screw is vaporized. I prefer manually installing a fat #8 or #4 copper wire between neutral bar and ground bar... if it's the only connection, you can put a clamp ammeter around it!

Be wary of a dangerous voltages and arc flash when connecting the neutral-ground bond. Better to turn off the main breaker while installing it. But there's even a small possibility the source of the current is external to your home. Just watch it.

Current flows on a neutral-ground bond because current actually wants to get back to source. For man-made power, source is the pole transformer and its neutral wire. The neutral wire is grounded to earth at the transformer. For lack of a neutral-ground bond, fault current may be traveling via your house's grounding system, to the DVR and TV cable jacket, the dirt around your home and back to the transformer's ground rod. A lot more current wants to flow, but dirt is a poor conductor. That'll change somewhat when it rains.

The second problem: a ground fault

A broken grounding electrode or N-G bond, alone, will not cause current flow. That would simply give you an isolated system. What's causing current to flow is a second problem: A hot-ground fault somewhere in your house. This could be in the wiring of a circuit, or more likely in an appliance.

It's easy to test an appliance with a 3-prong plug: take it into the bathroom and plug it into the bathroom GFCI. This test will best work if the GFCI is grounded, and your neutral-ground bond is in working order.

If you fix the neutral-ground bond and the grounding electrode system, current will flow down the intended emergency paths instead of the cable TV cable. (Actually it will flow down all at once, in proportion to their conductance; conductance is 1/resistance... But if your grounding systems are tip top, they should carry 99.9% of it and that will keep thongs from burning out.) This will be safer, but still spinning your electric meter. So it is costing you money not to find this ground fault. coughcheapCheesePCpowersupplycough

Your house needs a working grounding system. But if that's too much right now, you can put a band-aid on the problem by doing a bathroom GFCI test and fixing any appliances which trip the GFCI.

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