I am plugging my TV into a grounded outlet. When I plug an HDMI cable into the back of the TV and measure the voltage coming out of the other end of the cable (should be 0 shouldn't it?) it reads 380 volts...

I'm talking to my landlord about this but this is absolutely not normal is it? If so, what could be causing this? It happens with other outlets as well.


PAST INFO: When the first Comcast guy came and tried to install the X1 box, he got a little shock while trying to connect the two. He told me that the outlet I was plugging them into was reversed wired. The landlord fixed this and I confirmed that he did with a plug in tester. After this, Comcast came back and tried to install it again, same sparking issue.

I had two TVs with this problem

  1. TV #1 (3 pronged) was in my bedroom and was plugged in, and hooked up to a Comcast Digital Receiver with an HDMI cord. Worked perfectly. When I moved it into my living room and tried it with the Comcast X1 HD box, it created sparks when I tried to connect the two with an HDMI. The Comcast technician verified that no foreign voltage was coming out of the box or the HDMI from the box. He also replaced the box and the box's power supply. So this happened with two comcast boxes Could it be the Comcast box?
  2. TV #2 (3 pronged) was always located in the living room and created sparks after I plugged in the Comcast X1 box (both of the boxes).

NEW INFO: The two TVs that had high voltage coming from the HDMI cord that was plugged into the back of them had one thing in common. The power cords for those TVs had a ground on them (3 prong). My landlord brought his TV over and tested it and it worked. His TV has 2 prongs. I just bought a new TV and had an electrician come and we tested it, it worked. My new TV has 2 prongs. Could the three prongs be a problem with something?

My landlord used a Digital Volt Meter and had it set to the vAC option when it read 300+.

  • 7
    That's enough hint of a problem that you should for safety purposes assume the situation is hazardous until proven otherwise. In terms of understanding it though, the key question would be where your other meter lead is when you measure this voltage. Commented Aug 5, 2014 at 17:53
  • 1
    As Chris said, we need to know exactly how you measured this voltage.
    – Grant
    Commented Aug 5, 2014 at 21:46
  • 3
    How did you measure this voltage? Why did you measure the voltage? What settings did you have on your meter when you measured it? Is it DC or AC voltage? I wouldn't plug anything else into that cable until you can do a little more investigation.
    – pri0ritize
    Commented Aug 6, 2014 at 16:34
  • My landlord used a Digital Volt Meter and had it set to the vAC option when it read 300+. I also updated my question with more information. The comcast technician also used a Foreign Voltage Detector and it was coming back with high results when he waved it over the back of the TV.
    – Zack
    Commented Aug 7, 2014 at 12:22
  • 1
    So you touched both probes to the same piece of metal, and measured 380 VAC?
    – Tester101
    Commented Aug 7, 2014 at 13:04

4 Answers 4


You mention that there were sparks and a concern about your ground, I'd check for an incorrectly wired outlet as a precaution. The initial check is a simple outlet tester. These have 3 lights and quickly identify a hot ground or swapped neutral/hot, along with other common issues.

What they can't identify is if there's voltage on both the neutral and ground, for that, you'll need a known good ground and a simple voltage tester. For a known good ground, you can find some plumbing lines that are grounded, or perhaps the ground rods that the panel connects to, but a really easy way is to plug a long extension cord into a friendly neighbor's house and use the ground pin (in your case, the bedroom is probably a good ground). Check if there's voltage between the known good ground and your ground, or your neutral.

Since you're seeing actual sparks, I'm going to rule out phantom voltage from running an hdmi near electrical wires. And since the problem happened after you moved the TV, either the TV was damaged in the move, or it's another device that you added to the mix. Start with the outlet to be safe, but if that's not the problem, you likely had a faulty device. Given the reading of over 300V, I'm guessing that it was a faulty device. A hot/ground short would usually trip a breaker (unless it's not really grounded) and only read 120V.

  • I had an electrician come out yesterday and he tested the outlets in the room with a voltage detector. Could the mystery voltage be coming from the coaxial cable?
    – Zack
    Commented Aug 7, 2014 at 12:56
  • 2
    Is the coaxial cable plugged into the TV? If not, how would the voltage go from the coaxial to the TV to the HDMI cable if it's not attached? Very difficult to diagnose without more details on where you are testing the voltage and what is connected at the time. Start by disconnecting things to find the source. All you're going to get from the internet are guesses.
    – BMitch
    Commented Aug 7, 2014 at 13:04

Hi Ive seen this many times in my years as a uverse tech, we call it voltage bleed out. Faulty electronic components inside the tv bleed out high amounts of voltage (200+ VAC) through the hdmi ports onto our receivers making them fail or lose signal. We identify this issue by waving a Foreign Voltage detector anywhere near the surface of the tv and holding it close to the tip of an hdmi cable that is only connected to the tv. To solve this issue and stop potential revisits, our techs install grounding module blocks. These grounding modules plug into your outlet with three prongs and have a coax screw on the bottom that we use to attach a piece of coax to the coax screw in the back of the tv. The results are instant. You dont get any voltage readings with the FVD on the surface of the tv or on the connected hdmi cables. Sometimes every tv is bleeding voltage and we install one for every tv to protect the equipment. Its still a mystery as to why this happens as we see it on brand new and older tvs. Hope this helps.


I agree it is the bleed-out from faulty equipment, but my observation is slightly different. It is not always the TV that bleeds high voltage into the HDMI port. I have two Android TV Boxes connected with my two TVs out of which one is brand new, and have experienced voltage in both HDMI cables, before even inserting into the TV. So in my case, the voltage, which produces a spark comes out of the TV Box and NOT the TV. Since my TCL TV has a metal bezel, it gives a shock when we touch the outer most bezel when the TV Box is connected to it whether turned on or off. Once I plug out the power from the TV Box or take the HDMI cable out of the TV or the box, everything turns to normal. It therefore suggests that not in all cases, the TVs are faulty, it could be the media box being used.

The moot question therefore is that IS THE BLEED OUT FROM MEDIA BOX DANGEROUS FOR THE TV? Cause the Media Box costs 20 times less than the TV itself :-)


Coax grounding module

When grounding a TV, we use one of these modules. We plugged the module into a grounded outlet and attach a piece of terminated coax wire going from the coax lug on the back of the TV to the coax lug on the module. All V bleed out disappears when testing devices with FVDs after grounding.

Ground wire version

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