Source of 57 volts on coax cable

AZsparky

Senior Member
Location
Scottsdale, AZ
Sorry, I don't seem to be able to make my actions clear by my ramblings. This is what I meant: I drove a small ground rod in the middle of the back yard and used that as my reference point for all measurements to ground. I meant that my measurement reference point was now separated from the residence GES. Is that what you were referring to?
 

kwired

Electron manager
Location
NE Nebraska
Sorry, I don't seem to be able to make my actions clear by my ramblings. This is what I meant: I drove a small ground rod in the middle of the back yard and used that as my reference point for all measurements to ground. I meant that my measurement reference point was now separated from the residence GES. Is that what you were referring to?
Sorry, I misread what you said before. Yes you did good. If you have 50 volts from cable to this isolated reference the voltage about has to be coming from the cable someplace. I would say disconnect at cable companies main entrance and check there - if it is coming from their side it is really their problem. Show the technician your measurements if they don't want to believe it. Problem could be at some neighbors place.
 
Sorry, I misread what you said before. Yes you did good. If you have 50 volts from cable to this isolated reference the voltage about has to be coming from the cable someplace. I would say disconnect at cable companies main entrance and check there - if it is coming from their side it is really their problem. Show the technician your measurements if they don't want to believe it. Problem could be at some neighbors place.

One of the first things he did was test the incoming cable line and read no voltage.
 

AZsparky

Senior Member
Location
Scottsdale, AZ
Yes, I had disconnected the coax at the entry point to the home as one of my first TS steps. NO voltage present on cable company feed to house. Voltage is only present on the HOUSE side coax coming from the outside coax splitter and ONLY when the TV and Cable box are plugged in AND this coax run is connected. If the coax is not connected to the plugged in TV or converter = no voltage on coax. Running an extension cord to feed the TV and Converter with a different circuit yields the same results.
 

kwired

Electron manager
Location
NE Nebraska
Yes, I had disconnected the coax at the entry point to the home as one of my first TS steps. NO voltage present on cable company feed to house. Voltage is only present on the HOUSE side coax coming from the outside coax splitter and ONLY when the TV and Cable box are plugged in AND this coax run is connected. If the coax is not connected to the plugged in TV or converter = no voltage on coax. Running an extension cord to feed the TV and Converter with a different circuit yields the same results.
Somehow I missed that you said this also - not batting that well - count is now 3-2 am I going to strikeout, walk, hit? My homerun average is not good at all.

Outside of polarity problem with receptacle the TV or converter is plugged into - I would say there is a problem in one of those devices.

Maybe also verify integrity of the neutral and equipment grounding conductors supplying the receptacle. Place at least 1000 watt load on each of them and check how voltage responds. If the coax is bonded to a chassis that is also bonded to neutral you will have raised voltage on the coax if there is a neutral problem as the neutral is trying to find a path through any available conductive material it can.

Another question - is cable connected to intersystem bonding like it is supposed to be?
 

hurk27

Senior Member
Yes, I had disconnected the coax at the entry point to the home as one of my first TS steps. NO voltage present on cable company feed to house. Voltage is only present on the HOUSE side coax coming from the outside coax splitter and ONLY when the TV and Cable box are plugged in AND this coax run is connected. If the coax is not connected to the plugged in TV or converter = no voltage on coax. Running an extension cord to feed the TV and Converter with a different circuit yields the same results.
I have a question.
When you were checking the TV and the cable box, did you have all other cables like audio and HDMI disconnected between them? if not it might be the reason it's looking like both are causing the problem, isolate them from each other then plug them in one at a time to see if one or the other is the problem, then with everything disconnected using you isolated ground or just use the coax and measure the voltage between it and each item by going to the threaded part of the F connector (where you screw the coax on to) you might find that one or the other has a hot chassis
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Wayne, I believe he said that nothing was connected between the box and TV way back in the beginning.

I have a question that you still haven't answered- I'm thinking that you are measuring this voltage at the cable end outside the house but then you mention between the cable and a receptacle ground pin. Is there voltage between the cable box input connector to ground with the cable disconnected? You imply that there isn't, so how do you explain a straight piece of cable not connected to anything causing this?

-Hal
 

AZsparky

Senior Member
Location
Scottsdale, AZ
No strikeouts here guys...Except maybe on my part. I just really appreciate a second set of "eyes" on this issue. One of the things I should refresh memories on here is that there is a second TV and converter set on its own coax run that is also sending about 42 volts back to the outside splitter. It is on separate circuit. The circuits involved feeding the TV's are the same phase. Lets say they are circuits 10 and 14. The cable splitter at the point of entry to the home is bonded to the service riser with a # 10 solid copper. I did a load test at the service panel to see how the voltages reacted. I applied a 120 volt load (microwave) and a 240 volt load dryer. Voltages at the panel remained solid during load test (each phase to ground and phase to phase). So, if there was a loose neutral, there would have to be several downstream neutral connections loose, as each TV setup (each has its own circuit) introduces voltage back on to the coax, and I even temped up a separate circuit from an extension cord from a third circuit to feed one set with the same results of voltage going back to the coax entry point. The TV cords are OEM and are not grounding types, just two prong. Same with the converter boxes.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
I have a question that you still haven't answered- I'm thinking that you are measuring this voltage at the cable end outside the house but then you mention between the cable and a receptacle ground pin? Is that inside at the cable box/TV location?

Is there voltage between the cable box input connector to ground with the cable disconnected? You imply that there isn't, is that correct? If so how do you explain a straight piece of cable not connected to anything causing this?

-Hal
 
No strikeouts here guys...Except maybe on my part. I just really appreciate a second set of "eyes" on this issue. One of the things I should refresh memories on here is that there is a second TV and converter set on its own coax run that is also sending about 42 volts back to the outside splitter. It is on separate circuit. The circuits involved feeding the TV's are the same phase. Lets say they are circuits 10 and 14. The cable splitter at the point of entry to the home is bonded to the service riser with a # 10 solid copper. I did a load test at the service panel to see how the voltages reacted. I applied a 120 volt load (microwave) and a 240 volt load dryer. Voltages at the panel remained solid during load test (each phase to ground and phase to phase). So, if there was a loose neutral, there would have to be several downstream neutral connections loose, as each TV setup (each has its own circuit) introduces voltage back on to the coax, and I even temped up a separate circuit from an extension cord from a third circuit to feed one set with the same results of voltage going back to the coax entry point. The TV cords are OEM and are not grounding types, just two prong. Same with the converter boxes.


Is this what you meant to say? If so, I assume the riser is rigid metal and is bonded to the GEC.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Is this what you meant to say? If so, I assume the riser is rigid metal and is bonded to the GEC.
What does it matter?? He says the cable is disconnected from that splitter and is just hanging there!!

I really think we are getting way off base with ideas and also going around in circles.

-Hal
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Ok, just because you guys are annoying me with this I just went and pulled all the cables off a cable box I have here and guess what. I measure 55.8 volts between the metal on the rear of the box and the ground pin of the wall receptacle.

So I submit that this is four pages of nothing.


-Hal
 

kwired

Electron manager
Location
NE Nebraska
Ok, just because you guys are annoying me with this I just went and pulled all the cables off a cable box I have here and guess what. I measure 55.8 volts between the metal on the rear of the box and the ground pin of the wall receptacle.

So I submit that this is four pages of nothing.


-Hal

Four pages of nothing?

My settings are for 40 posts per page so we are still on page 1:D

We may have gone in circles some but I don't think it was all for nothing.

Maybe that kind of voltage is normal I don't really know. If it is not present when measuring with a low impedance meter I would probably not be concerned - yet the OP has the cable provider telling him there is an unacceptable voltage there and he either needs to cure it or prove it is normal.
 

texie

Senior Member
Ok, just because you guys are annoying me with this I just went and pulled all the cables off a cable box I have here and guess what. I measure 55.8 volts between the metal on the rear of the box and the ground pin of the wall receptacle.

So I submit that this is four pages of nothing.


-Hal
I've been waiting for a response like this. I actually went through this years ago and determined then it was common place, but I don't remember if we came to a definitive answer as to the technical reasons.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Well, I was trying to get the OP to be logical and check the most likely first. It should have been a big hint when there were two locations in the house with the exact same problem. It also makes no sense for a length of open cable connected to the input of the box or TV to be generating voltage. I actually do remember this subject from some place several years ago, I can't remember if it was here. I kinda think it actually was the cable techs board. What happens is that with TV and cable boxes there are always at least capacitors from each side of the line to chassis ground for noise filtering. It's due to those caps that you will see a voltage from the chassis to ground with an ungrounded line cord. Put a load on to though and it will dissappear.

As for the cable tech, there certainly have been cases of open neutrals and power crosses but they are not qualified to determine something like that. So as soon as they see a voltage they blame the wiring.

-Hal
 
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