DVR box chassis energized

Discussion in 'Electrical Forum discussion & Blog' started by nukeman, Oct 18, 2011.

  1. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    The other day, I was messing with some cable connections for my cable internet. When I leaned my forearm across the DVR box to disconnect the cable from the wall, I felt a shock. I dug out the multimeter and show 62 VAC from the box chassis to the cable connector. Not being sure if the voltage was being fed from the CATV jacket or if a fault in the box, I checked the voltage between the chassis and building electrical ground, I also get ~62 VAC, so it is the box being energized.

    I unplugged the DVR box electrical supply expecting the voltage to drop to 0, but instead held at 58 VAC. What I did find is that is that if I unplug the HDMI cable from the box, this voltage goes away. So, somehow this voltage is coming through the HDMI cable between the DVR and TV.

    TV and DVR box are 2-prong power cords. I'm not sure if the CATV is properly grounded as I did find a loose wire outside that says it is for CATV ground and looks like it might have been tied to an old A/C disconnect box or possibly an old phone box that is no longer there. Doesn't seem related at this point, but thought I would include it.

    One thing that I thought about is a fault in the DVR that shows up when it switches to HDMI output. I haven't tried other video outputs, cables, etc. yet.

    I'm going to look into it a bit more, but thought that I would post to see if anyone had come across a similar situation.
  2. ActionDave

    ActionDave Electrician

    Messages:
    345
    Location:
    Colorado
    A mis-wired receptacle, hot and neutral reversed, is something to look for.

    Cable TV should be grounded to the same wire as the grounding electrode conductor for the electrical service.
  3. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    Thanks, Dave. It wouldn't surprise me after seeing some of the electrical stuff in this house. I ended up rewiring the entire basement. This problem is on the 1st floor.

    Some things that I found in doing the basement:

    - hidden junction box with 2x the max number of conductors stuffed in
    - one room was being powered by 4 different circuits from the 1st floor
    - A/C disconnect box (metal) was not bonded. Looks like they faked it with the ground wire coming from the A/C unit to the disconnect, but there was nothing bonding the box to the electrical panel (12/2 wire without ground)
    - WH was not bonded...home inspector found this and was fixed before moving in
    - Romex run through 2x2 furring without protection plates
    ...etc.

    That's just the electrical issues. Also found hacked joists, unvented plumbing, crappy framing, etc.

    Just had the final electrical/mechanical inspection on the basement and passed. The inspector took the time to test every outlet down there, so I know everything is good there. Sounds like I should do the same thing on the other floors to see if something is reversed.

    Kent
  4. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    Used a plug-in tester and hot/neutrals are correct. Both the TV and DVR have polarized plugs and don't look to be reversed.

    I did add a supplemental ground rod not long ago and the bare copper wire for this rod runs near where that loose CATV ground connection is. I can clip the CATV ground onto this and see what we end up with.

    I'll try a few things over the weekend and see if I can figure out what is going on (if it is the TV, the DVR box, the HDMI cable, etc.).
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,531
    Location:
    North Carolina
    The grounding electrode conductor from the CATV should be a #12 and it is required to be bonded to the grounding electrode system of the premises wiring.

    As to the problem with a reading from the chassis of the box I would call in the CATV people and tell them to fix the problem
  6. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    Thanks, jw. It looks smaller than #12, but will take a closer look. From what I can see, it isn't bonded at all. The cable comes down from the pole, hits a splitter on the side of the house, then runs inside the house from there. This ground wire goes around to the back of the house (near where SE/meter is locatated). The wire is tagged saying it is for CATV ground, do not disconnect, etc. The wire is connected to a triangular looking connector which looks like it is made to clamp onto a corner of a box, but is just dangling there with the only thing really in reach of it is the A/C disconnect (which previously wasn't bonded either).

    Anyway, before calling, I want to see if it is a CATV problem (DVR box, cable itself) or if it is something else (TV, HDMI cable, etc.).

    The CATV guys around here aren't very good techs from what I have seen. They tend to just replace stuff until it works (instead of test) and probably would have a hard time getting them to even show up as the cable works and would probably tell me to call an electrician or the power company.
  7. BobL43

    BobL43 DIY Senior Member

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    Location:
    Long Island, NY
    From all I have read here from you, I think if you disconnect all the cables from the DVR box and just have it plugged in to power, if you measure the voltage from the DVR chassis to a good ground (you already did!) you will measure the voltage you did, not necessarily due to a fault in the box, but due to capacitance from live circuits in the box and/or TV (through HDMI cable shield) to the chassis and no third (ground) prong to drain it away. But measuring that voltage from a good ground to the cable sheathing or connectors sounds totally wrong, as it should be connected to ground through the F59 cable connectors and splitters, whatever all the way back to the premises grounding as JW said. That sound like more than a "phantom voltage".
  8. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    I also would expect the cable connectors to be at the same potential as the chassis (like you say through the connectors, sheathing, etc.) unless this path is broken. I'll test the cables and see if there is a break in the sheathing/connectors. The cable connector on the DVR box does look like it is electrically connected to the chassis (not isolated), but will verify that this path is there too.

    With HDMI unplugged, but box still powered (I believe cable was also disconected at this point, so only power connected), the phantom voltage on the box was a couple volts above a good ground. As soon as the HDMI is connected, it shoots to 58VAC (power disconnected from box) or about 62 VAC with power connected. It also not a momentary charge (like static electricity) as if I touch the box along with any decent path to ground, I get a decent jolt from it. This is why I wonder if the CATV is actually bonded somewhere that I haven't located (and current is flowing threw me to that path) or if that connector/sheathing is bonded back at the pole and current is going that direction.

    The box is on a glass shelf and not touching anything else, so we can elimate the box being energized from another box directly (DVD, whatever) (box to box contact, I mean).
  9. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,786
    Location:
    Long Island, NY
    For ***** and giggles, you might want to hook up a low wattage (4 watt night light bulb) and a pigtail socket (wear your plasma suit and other safety gear) to see if there is any current available that can light up this little bulb; if it can, then there is indeed a dangerous situation.
    Last edited by a moderator: Oct 20, 2011
  10. ActionDave

    ActionDave Electrician

    Messages:
    345
    Location:
    Colorado
    Good advice in a way. I use a solenoid tester with a digital meter, however he did say he felt a shock that was sustained. That seems to rule out phantom voltage. If the circuit that the box is plugged into is okay then the possibility of a neutral problem at the house or neighbors house is a possibility.

    I don't know how the HDMI cable plays into this, but I would get the cable bonded to the main service earth ground. I might also try turning off breakers one by one and see if the voltage goes away. I would keep the box unplugged until I solved the problem.
  11. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    I tested for voltage again last night and now the voltage isn't there??? I'll make sure the CATV is bonded and will keep an eye on it.

    The HDMI thing was weird too. Seems like that would only deal with low voltage signals unless switching to the HDMI output was activating a portion of the circuitry in the box where the fault was located...

    I also checked for continuity between the chassis and the cable connectors and all looks good there (which seems to mean the the voltage difference shouldn't have been there even if not bonded). Perhaps the sheathing is damaged somewhere and contact is breaking when the cable is bent a certain way? Who knows...It is a mystery at this point and I can't really test it until the problem returns.
  12. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,786
    Location:
    Long Island, NY
    Solenoid tester? you mean the old Wiggy? I still have mine from the 70's. I think that might draw too much current and pull the voltage down to zilch. I need to measure what mine draws at 115VAC

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