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Old 01-01-2013, 10:29 AM   #1
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Voltage on my ground leg


I recently bought a new tv and plugged it in to my cable box upstairs and then plugged the tv into the outlet. Then the tv downstairs went out and something in the main cable connecting equipment to the house (outside) blew up. The cable guy came out and said there was a short to ground in my NEW tv. He went on to say that this was the third one this week.

So, this morning, skeptical of his diagnosis, I checked voltage from the ground plug in the receptacle to the ground (outer metal covering) on my HDMI cable, which was plugged into the cable box. I read 118VAC. Seeing as how I can touch the outer metal covering of the HDMI cable without my hair standing up, I suspect I have voltage on my ground leg.

I have an old house with k&t wiring upstairs, but Romex downstairs. Seeing as how not everything that was plugged in was destroyed (only the stuff connected to CATV) the problem must be in that circuit. However, everything worked fine until I plugged in a new tv upstairs. The other tv was connected exactly the same way.

Im perplexed. Please HELP!!!

Thank you

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Old 01-01-2013, 10:46 AM   #2
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Voltage on my ground leg


IMO this is nothing you'll be able to troubleshoot yourself. You need someone with the tools and expertise to check out your whole system.
Sound like someone replaced some non-grounding receptacles with grounding type and you have a fault somewhere.

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Old 01-01-2013, 10:47 AM   #3
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Voltage on my ground leg


You could start by disconnecting EVERTHING on the suspect circuit, measure voltage between hot and neutral, between neutral and ground, and between hot and ground. Neutral to ground should be 0 volts. This is best done with a wiggy or analog meter. Digital multimeters may read phantom voltages.
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Old 01-01-2013, 10:55 AM   #4
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Voltage on my ground leg


I'm gonna call BS on this one, assuming everything the OP has stated is true.

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So, this morning, skeptical of his diagnosis, I checked voltage from the ground plug in the receptacle to the ground (outer metal covering) on my HDMI cable, which was plugged into the cable box. I read 118VAC. Seeing as how I can touch the outer metal covering of the HDMI cable without my hair standing up, I suspect I have voltage on my ground leg.

I have an old house with k&t wiring upstairs
If you have ungrounded wiring upstairs, you wouldn't read 118V even if the HDMI had voltage on it.
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Old 01-01-2013, 11:01 AM   #5
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Voltage on my ground leg


Your problem may be with that Knob & Tube wiring, here is a link describing some of the short comings of this wiring. One of which is no safety grounding conductor..http://en.wikipedia.org/wiki/Knob_and_tube_wiring
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Old 01-01-2013, 11:01 AM   #6
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Bootleg ground on the wrong wire of the knob and tube?
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Old 01-01-2013, 11:01 AM   #7
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Voltage on my ground leg


just double checked. Romex to rept. upstairs. Ground is def hot. Ground to neutral=118vac, hot to neutral=118vac, ground to hot=8vac.

So I wouldn't actually call it BS so much as an error on my part.
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Old 01-01-2013, 11:03 AM   #8
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There is some k&t wiring upstairs but only for lighting. recpts are Romex
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Old 01-01-2013, 11:17 AM   #9
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Best I can tell, right now, someone spiced the romex off the k&t wiring upstairs and obviously did so incorrectly. Those of you who provided actual, useful answers, I am greatly appreciative. You can always tell the professionals.
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Old 01-01-2013, 11:21 AM   #10
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Did you find the problem or are you just making assumptions?
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Old 01-01-2013, 11:22 AM   #11
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Voltage on my ground leg


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Originally Posted by k_buz View Post
If you have ungrounded wiring upstairs, you wouldn't read 118V even if the HDMI had voltage on it.
The scenario is plausible if the outlet is not grounded, but the cable is.

I had something sort of like this happen when I was finishing my house. An electrician had done the rough, but then the GC abandoned the job, and I wound up doing the finish wiring myself. One day I noticed that I was getting a buzz off of a light switch in the garage. I stupidly touched a cover plate screw, and it popped me.

Opening the box up, I found that the bare ground was touching the hot screw. "OK", I thought, "that explains why the switch body was hot. But why didn't the breaker trip?" Tracing the circuit back, I found a box where a smoke detector was mounted, where the electrician had not tied the grounds together. Everything on the circuit past that had a floating ground. (Fortunately, it was only a few lights, no receptacles.)

I wonder if something like this has happened to the OP, given the age of his house and the mix of wiring methods: The outlets in question are wired with romex with ground, but it's being fed by K&T or older romex without ground. Therefore, the ground doesn't actually extend back to the panel and therefore is floating. Something shorts to ground somewhere, either in the circuit or in something that is plugged in, and the ground becomes hot.

I'd start by unplugging everything on the circuit. Then test for voltage between a receptacle ground and a known good ground. If there is voltage, there's a hot-to-ground short in the circuit. Take the cover plates off of all the devices on the circuit and look for a bare ground wire touching a hot. If there is no voltage, plug everything back in one at a time, checking for voltage on ground after each one.

Either way, the ground should not be floating. If getting the ground extended back to the panel is impractical, then the circuit will need to be protected by a GFCI.
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Old 01-01-2013, 11:29 AM   #12
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Voltage on my ground leg


Let's see. Well, the romex runs to the knob and tube wiring and disappears under an excessive amount of electrical tape and doesnt come out. It is a short run of romex...maybe 9 feet to the recpt. Im calling it an educated guess. You can call it an assumption.
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Old 01-01-2013, 11:35 AM   #13
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Quote:
Originally Posted by fa_f3_20 View Post
The scenario is plausible if the outlet is not grounded, but the cable is.

I had something sort of like this happen when I was finishing my house. An electrician had done the rough, but then the GC abandoned the job, and I wound up doing the finish wiring myself. One day I noticed that I was getting a buzz off of a light switch in the garage. I stupidly touched a cover plate screw, and it popped me.

Opening the box up, I found that the bare ground was touching the hot screw. "OK", I thought, "that explains why the switch body was hot. But why didn't the breaker trip?" Tracing the circuit back, I found a box where a smoke detector was mounted, where the electrician had not tied the grounds together. Everything on the circuit past that had a floating ground. (Fortunately, it was only a few lights, no receptacles.)

I wonder if something like this has happened to the OP, given the age of his house and the mix of wiring methods: The outlets in question are wired with romex with ground, but it's being fed by K&T or older romex without ground. Therefore, the ground doesn't actually extend back to the panel and therefore is floating. Something shorts to ground somewhere, either in the circuit or in something that is plugged in, and the ground becomes hot.

I'd start by unplugging everything on the circuit. Then test for voltage between a receptacle ground and a known good ground. If there is voltage, there's a hot-to-ground short in the circuit. Take the cover plates off of all the devices on the circuit and look for a bare ground wire touching a hot. If there is no voltage, plug everything back in one at a time, checking for voltage on ground after each one.

Either way, the ground should not be floating. If getting the ground extended back to the panel is impractical, then the circuit will need to be protected by a GFCI.
Thanks, I've gotta go to work but I will definitely try your suggestion tomorrow.
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Old 01-01-2013, 11:36 AM   #14
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Voltage on my ground leg


[quote=patrickmcdiver;1083884]I recently bought a new tv and plugged it in to my cable box upstairs and then plugged the tv into the outlet. Then the tv downstairs went out and something in the main cable connecting equipment to the house (outside) blew up. The cable guy came out and said there was a short to ground in my NEW tv. He went on to say that this was the third one this week.

So, this morning, skeptical of his diagnosis, I checked voltage from the ground plug in the receptacle to the ground (outer metal covering) on my HDMI cable, which was plugged into the cable box. I read 118VAC. Seeing as how I can touch the outer metal covering of the HDMI cable without my hair standing up, I suspect I have voltage on my ground leg.

I have an old house with k&t wiring upstairs, but Romex downstairs. Seeing as how not everything that was plugged in was destroyed (only the stuff connected to CATV) the problem must be in that circuit. However, everything worked fine until I plugged in a new tv upstairs. The other tv was connected exactly the same way.

Im perplexed. Please HELP!!!

Is the receptacle your testing on the knob and tube wiring ?

Is it a 2 prong receptacle or 3 prong?

Is your new tv a 3 prong plug or 2 prong ?

If the receptacle is two prong and your testing to the neutral then it could be wired reverse of normal ..ie.. hot to the neutral side and neutral on the hot side. This would explain the voltage reading to the ground of the HDMI when you test.

If it is 3 prong and a bootleg ground was installed and the receptacle is wired reverse .. if you plug a 3 prong plug into it you would energize the the ground of the tv which would travel to the hdmi cable.

It is very common to see knob and tube wiring reversed on receptacles and in some cases this can cause problems.

Last edited by Stubbie; 01-01-2013 at 11:51 AM.
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Old 01-01-2013, 11:56 AM   #15
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The ungrounded K&T should not have been extended.

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