Source of 57 volts on coax cable

AZsparky

Senior Member
Location
Scottsdale, AZ
Anybody run into this before? Got a customer who called reporting that the cable TV tech told her that they had 57 volts coming to their cable box converter and to call an electrician. First thing I plan to do is break the connection at the point of entry to the home to see if the source is upstream or downstream. If it's inside the home, it would seem to be something associated with grounding... Anybody experience this before??
 

AZsparky

Senior Member
Location
Scottsdale, AZ
I believe the tech thought that the voltage he was measuring was the reason why 2 converter boxes had gotten fried. I don't know what meter he used, but it seems as if there is a problem. I'll know a lot more once I get out there tomorrow. I was just wondering if anyone has seen this before...
 

iwire

Moderator
Staff member
Location
Massachusetts
An open or high resistance connection on the neutral between the home and the transformer could do it. The condition could even be traced back to a neighbor's home.
 

AZsparky

Senior Member
Location
Scottsdale, AZ
Thanks for the reply. Yes, my first part of troubleshooting will be to break the connection at the coax cable point of entry to the home. see if the source is inside or outside of the homes wiring. I'll post what I find out...
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Thanks for the reply. Yes, my first part of troubleshooting will be to break the connection at the coax cable point of entry to the home. see if the source is inside or outside of the homes wiring. I'll post what I find out...
be careful. If it is really 57V you could become the conductor when you open it up.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
Anybody experience this before??
There is a missing ground on a power supply. There are 2 equal capacitors tying both "black" to "green" and "white" to "green". With no connection from the power supply egc to the source's "0V" (neutral/ecg in service), you'll see that. I do frequently with notebook power supplies in my instrumentation systems.
 
Last edited:

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Pay attention to what is on inside the house before you break that connection! I have had a condition like you are describing. iwire & perersonra both have good points. You may want to get POCO involved. You could burn up her appliances by breaking this connection. The 57 volts could have been what he measured at that particular time. Here:http://forums.mikeholt.com/showthread.php?t=144448&p=1390836&highlight=#post1390836
 

AZsparky

Senior Member
Location
Scottsdale, AZ
Update on coax voltage

Update on coax voltage

Thanks all for your input and suggestions.

Had a little time to visit this home today and found this:

Disconnected all coax at outside 3-1 splitter. I think only 2 coax are being utilized inside the home. NO voltage measured on feed from cable company. 32.5 volts measured on each of two coax entering home. Turned off breakers until voltage was gone. Identified and marked the (2) separate 15 amp circuits involved. One was feeding the TV and converter box in the MBR, and the other was feeding the TV and cable converter box in the FR. If I unplugged both the TV and the Converter box at the MBR and the voltage on the coax was gone. Plugging either one of them back in reintroduced the voltage, although there was no longer ANY type of connection between the TV and the cable box ~ No HDMI, no coax, etc. So, if either unit was plugged in and the coax connected back to it the 32.5volts would again be present on the coax. It didn't matter which one, the voltage would again be present. If the coax was not connected to either unit with the circuit on, the voltage would not be present. So when either one of the units was energized and connected to the coax, the coax would get the voltage again. I did not have time to take it farther, but at this point am assuming the other TV and cable converter box are doing the same thing on the other circuit. The two circuits involved are the same phase. The cable splitter back at the point of entry to the home is bonded ~(confirmed with a continuity test) back to the GES. Voltages at the panel measured in the normal ranges under load conditions (microwave, dryer). Receptacle feeding MBR TV/converter box tested fine. No interference on TV signal as pictures on both TV's were beautiful. Any ideas on this updated info?
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Your explanation is a little confusing. Are you saying that you narrowed it down to the TV and cable box in the MBR but you suspect the same is happening in the FR? Specifically, with no connection between the TV and cable box, plugging a line cord from either the TV or the cable box into the receptacle causes a voltage to appear on the disconnected cable end outside the house that is connected to that cable box's input?

Where are you measuring this voltage- from shield to ground or center conductor to ground- or what?

What kind of meter are you using?

If you disconnect the cable from the cable box do you measure the voltage on the input connector using a short piece of cable?

If the TV is not connected to the cable box in any way how would plugging the TV line cord into the receptacle cause voltage to appear on the cable to the cable box when the cable box line cord is not plugged into anything? This is what casts suspicion on he whole situation. I'm also inclined to conclude phantom readings due to a high impedance meter.


-Hal
 

hurk27

Senior Member
Thanks all for your input and suggestions.

Had a little time to visit this home today and found this:

Disconnected all coax at outside 3-1 splitter. I think only 2 coax are being utilized inside the home. NO voltage measured on feed from cable company. 32.5 volts measured on each of two coax entering home. Turned off breakers until voltage was gone. Identified and marked the (2) separate 15 amp circuits involved. One was feeding the TV and converter box in the MBR, and the other was feeding the TV and cable converter box in the FR. If I unplugged both the TV and the Converter box at the MBR and the voltage on the coax was gone. Plugging either one of them back in reintroduced the voltage, although there was no longer ANY type of connection between the TV and the cable box ~ No HDMI, no coax, etc. So, if either unit was plugged in and the coax connected back to it the 32.5volts would again be present on the coax. It didn't matter which one, the voltage would again be present. If the coax was not connected to either unit with the circuit on, the voltage would not be present. So when either one of the units was energized and connected to the coax, the coax would get the voltage again. I did not have time to take it farther, but at this point am assuming the other TV and cable converter box are doing the same thing on the other circuit. The two circuits involved are the same phase. The cable splitter back at the point of entry to the home is bonded ~(confirmed with a continuity test) back to the GES. Voltages at the panel measured in the normal ranges under load conditions (microwave, dryer). Receptacle feeding MBR TV/converter box tested fine. No interference on TV signal as pictures on both TV's were beautiful. Any ideas on this updated info?

I had one like this that was caused by a reversed polarity wired receptacle the wiring was reversed in the ceiling light box, not only was the receptacle reversed polarity but the GEC to the grounding terminal was boot legged from the hot neutral in ceiling the light box which would show as a correctly wired receptacle using a 3-light plug in tester, this is a very dangerous set up as anything plugged in this receptacle would have a hot chassis as the ground was connected to the hot instead of the neutral, so you might want to get an extension cord from a known good receptacle and test from it to find which wire is the true hot, neutral, and look for a bootleg ground, the bootleg ground may or may not be present to cause the problem.

A second call was an older CRT TV that turned out to be a hot chassis, older CRT type TV's use caps to the neutral and or hot, if a cap to the hot shorted it would cause voltage on the chassis, these sets only had a two wire cord so they didn't really have a reference to ground except through these filter caps, but this would only cause the problem when only the TV was plugged in not the cable box, the previous call is what I would look for because both the cable box and TV are causing it, and the only common thing is the receptacle and or the circuit feeding it, you might take the receptacle out and find the hot and neutral wired correctly including the ground but using the extension cord you will find that the neutral wire is hot and maybe the ground is also, that means you have a bootleg ground off the neutral at or ahead of the receptacle, using the same extention cord from the known good receptacle if you plugged in the TV and cable box, it most likely wont have the problem, so then you will know where to look for the problem.

also make sure if they are using a plug strip that it isn't miss wired, wouldn't be the first time I found this problem not on a TV but in a garage being used for a freezer that the home owner was getting shocked from, the strip had a new plug end changed and the ground and neutral was wired to the hot terminal with the hot on the neutral, the freezer would run just fine but don't touch it bare foot as the cabinet was hot.

funny thing is a 3-light tester shows it wired correctly, and it can tell which wire is which in a case like this, as long as there is a 120 volts between the hot to neutral and hot to ground it will light the two lights correctly, this is why I say use an extention cord from a known good receptacle for a referance point. just remember the small blade is the hot and the large blade is the neutral and you cant go wrong unless you didnt make sure the receptacle you plugged it in to was wired right? but at least with an extention cord you can go to a water pipe or other grounded item and test it to make sure the hot is hot.
 
Last edited:

AZsparky

Senior Member
Location
Scottsdale, AZ
Update continued

Update continued

Sorry about not being concise. I'll try again. The only time there is voltage present on the coax cable (BOTH the center pin AND the coax shield to ground) with the ground being the ground prong of a nearby 120 volt receptacle) is when either the TV is plugged in or the converter box is plugged in AND the coax coming from the point of entry to the home is attached to the device plugged in. The coax cables are isolated from each other (taken off the splitter) at the point of entry. So, 32.5 volts is introduced onto the coax by plugging in either the TV or the Cable box. This is happening at both TV locations in the home that have a coax line. They have a modem at the other location (Family Room) which I have not been to yet, as it would involve moving a heavy entertainment center. So I'm hoping that knowing what is causing the MBR situation is likely the same cause for the Family room.

The meter I use is an Ideal # 61-704 with a shaker. The voltage is just high enough to activate the shaker.

On my trip back, I WILL run an extension cord from another circuit to power up the TV and converter box. They had a plug strip, but I took this out of the system right away. I'll also get into the receptacle feeding the TV and verify the wiring to it. I only used my plug tester on it and just the lights indicated it was wired correctly.

I'm going back Wednesday, so any other ideas would be greatly appreciated...
 

kwired

Electron manager
Location
NE Nebraska
What is the ground reference you are using for measurements?

The fact that you only have problems when a particular TV is in use likely means that it is not an issue with service neutral, but you must remember any voltage between the electrical service and the coax is just that - voltage. You still need to determine which one actually is at an elevated voltage above ground.

Reversed polarity at receptacle sounds like a good possibility. How old of a TV are we talking about? Most newer - especially LCD TV's do not even have an internal power supply anymore. If secondary of power supply is isolated from input - there is no grounding of the derived supply.
 

AZsparky

Senior Member
Location
Scottsdale, AZ
More info

More info

Both TV's are newer flat screens a couple of years old with non-grounded power supply. I'm really thinking there is some kind of "cowboy wiring" going on with the grounded conductor and/or the equipment ground somewhere. And I apologize to any legitimate electricians who are actual cowboys. Thanks to everyone for their input!
 

kwired

Electron manager
Location
NE Nebraska
Both TV's are newer flat screens a couple of years old with non-grounded power supply. I'm really thinking there is some kind of "cowboy wiring" going on with the grounded conductor and/or the equipment ground somewhere. And I apologize to any legitimate electricians who are actual cowboys. Thanks to everyone for their input!
Find some earthed metal object with no connection to the premesis grounding and is not right next to anything connnected to premesis grounding system and use that as your ground reference. Even a screwdriver pushed into the soil in middle of yard if that is all you can come up with. If you are using the buildings service ground and it happens to be compromised by a bad connection someplace you will be looking for the wrong thing because you assumed your reference is true ground.
 

Rick Christopherson

Senior Member
How was the 57 volts measured? If it was a high impedance meter it may well be meaningless.
I haven't read the rest ot this thread, but it always bothers me when I see someone say this. The voltage readings are not meaningless. They do mean something, and are actually more accurate. How someone interprets that accuracy is important.

Your analog meter is actually altering the circuit you are measuring by reducing the resistance between the test points. It becomes part of the circuit. Masking the information is not the same as it being meaningless. It does tell you something.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
The only time there is voltage present on the coax cable (BOTH the center pin AND the coax shield to ground) with the ground being the ground prong of a nearby 120 volt receptacle) is when either the TV is plugged in or the converter box is plugged in AND the coax coming from the point of entry to the home is attached to the device plugged in.
Yeah. I would suspect the receptacle being wired properly or something wrong with the wiring. I would also check the ground on that receptacle. Could be that the voltage is really on the ground pin, not the TV or cable box. Those LED testers can be fooled sometimes.

Is there voltage present on the input connector WITHOUT the cable connected? I think you said no. If the cable runs straight to the splitter outside (to which it isn't connected) why would it have to be connected to the TV or cable box for you to see that voltage? That leads me to believe that it isn't a home run at all, there is something else on that cable. I have found cables with splitters, ground blocks and splices buried under siding or other work during remodeling. Old cables were extended to the new drop and ground block location. Could be that there is a grounded splitter or ground block somewhere still connected to some kind of ground.


I think at this point I would run new RG6 to each location or at least temp one to see what happens.

-Hal
 

AZsparky

Senior Member
Location
Scottsdale, AZ
Update continued

Update continued

Well, here is the latest on the 50.2 volts on the coax. Established a separate earth ground (from building GES) for a reference point to check the wires coming into the receptacle feeding the TV and cable box in the MBR. All conductors tested appropriately. 124 volts hot to ground, 0 volts neutral to ground, etc. Ran an extension cord from a receptacle known to be on a different circuit than the master bedroom to feed the MBR TV and cable box ~ Same deal, 50.2 volts on the coax (the pin and the shield). One thing I did notice when I was able to get to the receptacle feeding the MBR TV, was that the ground wire was looped around the ground terminal, but the screw was never tightened down. As I stated before though, my receptacle tester showed the receptacle was wired correctly on my first brief visit. I verified this with a separate earthen ground today. NOTED TODAY: At the outside splitter, if I removed the coax feeding the MBR cable box from the outside splitter, the center pin and outside shield would measure 50 volts to ground. If I reconnected it to the splitter, the outside shield voltage would be gone. As I stated before, the splitter is bonded to the GES with a #10 solid copper. The TV and Cable box are what is putting this voltage onto the coax. I saw a post today on this forum from 2003 where the guy posting had run into this same scenario several times. I'll try to copy and paste that into a reply when I get a chance....
 

kwired

Electron manager
Location
NE Nebraska
Well, here is the latest on the 50.2 volts on the coax. Established a separate earth ground (from building GES) for a reference point to check the wires coming into the receptacle feeding the TV and cable box in the MBR. All conductors tested appropriately. 124 volts hot to ground, 0 volts neutral to ground, etc. Ran an extension cord from a receptacle known to be on a different circuit than the master bedroom to feed the MBR TV and cable box ~ Same deal, 50.2 volts on the coax (the pin and the shield). One thing I did notice when I was able to get to the receptacle feeding the MBR TV, was that the ground wire was looped around the ground terminal, but the screw was never tightened down. As I stated before though, my receptacle tester showed the receptacle was wired correctly on my first brief visit. I verified this with a separate earthen ground today. NOTED TODAY: At the outside splitter, if I removed the coax feeding the MBR cable box from the outside splitter, the center pin and outside shield would measure 50 volts to ground. If I reconnected it to the splitter, the outside shield voltage would be gone. As I stated before, the splitter is bonded to the GES with a #10 solid copper. The TV and Cable box are what is putting this voltage onto the coax. I saw a post today on this forum from 2003 where the guy posting had run into this same scenario several times. I'll try to copy and paste that into a reply when I get a chance....
As previously mentioned, you need to find a reference that is not connected to the electrical system. All you have proven with your measurements from both lines to this reference point is that there is no potential between the service neutral and the grounding electrode system which if the connection to GES is good that is what you should get. There could still be voltage between the electrical system ground and other grounded objects - including the TV cable because there is a loose neutral somewhere on the electrical supply. Take measurements again using an isolated grounding probe. You could easily have a small amount of voltage from neutral to this probe - that is voltage drop from whatever load is on the neutral but if you have 50 volts you have a problem. If the voltage is on the TV cable the problem is on the cable someplace.
 
Top