Overheated CATV wire

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sceepe

sceepe

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Just got a call from a friend during a rain storm. Said no CATV at his house but if he wiggled the wire it would come in. I said no problem, you have bad connection I'll be right over.

When I got there I found outer insulation on the cable from the dip pole was melted and swollen where it meets the first splitter. This splitter was grounded via a #12 to the grounded electrode conductor from the meter. Also noticed a small spark when I reconnected the cable to the splitter.

Do you guys think that there could be a short somewhere in the house that is resulting in current in the grounded electrode conductor and this is causing the connection I replaced to get hot enough to melt the insulation?

Or could there be a current from somewher imposed on the catv line coming into the house?

Is there enough energy in a normal CATV signal to cause enough heat (in a bad connection) to melt the insulation on coax?

I plan to go back in the am with a meter and see if I cam measure a current between the cable and the splitter. Would like to check for a voltage on the ground wire but I am not sure what I should measure across. The grounded electrode conduction is the reference I would normally use.

Thanks for your help
 
Are there any other problems? The most likely cause for current on the coax is a high resistance or open on the service grounded conductor. The code grounding and bonding rules require that the coax shield be a parallel path for the neutral.
Don
 
I've found two like this in the past. One resulted in one or two ruined television sets. In both cases, the root of the problem was a loose neutral at the neighbor's house.
 
sceepe said:
Do you guys think that there could be a short somewhere in the house that is resulting in current in the grounded electrode conductor and this is causing the connection I replaced to get hot enough to melt the insulation?

Or could there be a current from somewher imposed on the catv line coming into the house?
Click to expand...
What we're saying is that the problem is more likely that the house's (what should be) grounded conductor and grounding system is what has the voltage on it, not the incoming cable.
 
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Thanks for the replies guys. Sounds like three possible issues. Open neutral at poco xfmr, at neighbors house, and the house in questoin.

Now, do you have any idea how I should go about tracking this down?
 
Here is an update. Cable folks showed up, said problem was not on their line and to get an electrician. (What a surprise).

I went back with a meter. Disconnected all wires coming into the splitter. All cables read about 0-2 V from the coax shield to the grounded electrode conductor except for one. This one read 24V to ground, This had a dvd player and old tv on it. Disconnected the tv and got 2V to ground.

Conclusion: something wrong internal to tv that was allowing line voltage to show up on the coax shield.

Don you were saying that
The code grounding and bonding rules require that the coax shield be a parallel path for the neutral
Click to expand...
. Is this what you were talking about?
 
The coax shield is required to be bonded to the grounding electrode sytem at each house. The grounding electrode system is bonded to the grounded conductor at each house. Under normal conditions the impedance of this path is many times greater than that of the grounded conductor and only a very small amount of current will flow. When there is an open service neutral to one of the houses the coax is one of the lower impedance paths for the neutral current to flow on, but it doesn't have much ampacity and will overheat.
If the coax with the damage was on the street side of the splitter with the #12 grounding conductor, I doubt that you have found the problem. If it was on the house side, you may have found the problem.
Don
 
sceepe said:
Conclusion: something wrong internal to tv that was allowing line voltage to show up on the coax shield.
Click to expand...
If you get the chance, look at the TV's plug; is it polarized? If so, is the cord removable from the TV? If so, is it polarized? If not, is a non-polarized extension cord or other device in use? If not, is the receptacle properly wired?

What I am getting at is many TV's, especially older all-tube sets, often use the chassis as AC ground, and use bypass capacitors to connect the circuitry ground reference to the chassis. A reversed AC "polarity" makes the chassis hot.
 
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