DirecTV electrical issues?

March 2, 2010 9:31 AM

So, I've got an electrical problem in my house. Somewhere between my DirecTV installation and my house wiring, I am blowing up TVs...

Here's the skinny:

A friend of my moved into my basement a couple of months ago. I had DirecTV install a new line for him into his room. The DirecTV installer ran a new coax line, plugged in the box and connected the TV via HDMI.

BOOM! Dead TV and dead DirecTV box.

The TV is under a Best Buy service plan, so we had them fix it. It came back and the same thing happened.

Today, we got the TV back again. This time, a local TV repair guy brought it and hooked it up. Again, same thing.

Although he is not an electrician, he found that there was approximately 120V from the ground on the coax cable (the outer cooper) to the ground in the wall outlet. And there was enough current to give him a nasty shock.

A quick check of the outlet with a polarity tester shows that is wired correctly. We took the cover plate off the outlet, and everything is connected correctly. This is in the basement, so I can see the entire coax run and there aren't any nicks or cuts.

The ONLY thing that looks suspicious, is the coax follows some electrical lines through holes in the floor joists. Everything is insulated and fairly modern wiring. When I switch the circuit break off for the room in the basement where we are having issues, I no longer get any voltage. It's worth noting, the wiring next to the coax in the floor joists is on the circuit we have turned off. Could we be INDUCING a current in the coax? Or is it something else?

So, what the hell? I'd rather not have the house burn down...

posted by PhillC to home & garden (16 answers total)

Rule of thumb for this sort of thing: If you have done a reasonable amount of troubleshooting (and it sounds like you have) and you are still at "What the hell?" it's time for a professional electrician.
posted by sageleaf at 9:41 AM on March 2, 2010

My guess: you've got a ground loop, and a fairly nasty one. That is, an electrical outlet isn't grounded properly. Might be the one in the basement, might be another one elsewhere in the house where another TV (or some other device) is plugged into the coax.
posted by kindall at 9:44 AM on March 2, 2010

The Direct TV guy screwed up if there is voltage on the coax. That is why you always go with Dish Network. ;) Anyway, they need to send out a seasoned repair tech to sort this out for you. You probably want to talk directly to the field service manager.
posted by caddis at 9:49 AM on March 2, 2010

I'm about ready to call an electrician. Trying to see if it might be the DirecTV install. Most of my house is NOT grounded. In fact, my main TV, and one in another bedroom are plugged into two prong outlets.
posted by PhillC at 9:52 AM on March 2, 2010

Yeah, so.

First: 120V on the coax? It's coming from somewhere. Turn off the circuit breaker for the circuit breaker running adjacent to the coax, and there's no more 120V on the coax? Now you know where it is coming from.

The question is "why", and there are a couple of possibilities I can think of (IANAE):

1. That particular circuit has a break in the insulation, and the current is arcing into the coax, which has a nick. Possible.

2. That particular circuit is miswired/shorting to ground somewhere, and it is the same ground that the coax is grounded to. Possible.

3. The coax is not grounded, but is instead (somehow, I have no idea how) attached to a hot leg. Unlikely.

4. The coax is getting 120V induced into the ground. Unlikely.

So if I were you, I'd shut off the circuit breaker and have an electrician come out and figure it out (especially in case it's 1-2, which is dangerous beyond the coax voltage.) If you can't afford it right now or the electrician's schedule isn't agreeable, shut off the power and pull out the entire coax line, paying particular attention to where the coax cable was grounded, so that you can show the electrician later.

But as a rule, getting 120V in something that's supposed to be grounded is a huge red flag that you need an electrician stat, and keep that circuit shut off until then to be safe.
posted by davejay at 9:54 AM on March 2, 2010

Have you tried checking the coax-to-ground with the converter box unplugged? It may be shorted out inside the box. If it is still hot with the box unplugged, it is somehow coming from a short between external wiring and the cable. If it is hot only with the box plugged in, it is the box (something inside shorting) and not the wiring.
posted by Old Geezer at 10:05 AM on March 2, 2010

First, thanks to everyone. I think I am going to call DirecTV first. If they can't find anything, then I will move on to an electrician. If he points the finger at DirecTV, I'll go from there.

@davejay:

Seems like number 1 is not very likely. I just cannot see anywhere this has happened. Number 2 doesn't seem likely. A polarity tester connected to the outlet checks out. I would expect it to show if the ground on the outlet wasn't a ground at all.

I inspected the box on the outside of the house where all of the DirecTV lines are connected. There are connected to a valid ground (the main ground for the house). That should rule out number three.

And number four seems really unlikely, but it's about the only thing that makes sense. The wiring that the coax runs next too is the wiring to the room in question. So with the breaker off, I do not get any voltage from the coax to the ground in the outlet in the room. I don't see why the ground in that outlet wouldn't still be a ground if the breaker was off (unless it's a hot...)?
posted by PhillC at 10:11 AM on March 2, 2010

@old geezer:

I'm sure it's not the converter box. I've fried three of them...
posted by PhillC at 10:12 AM on March 2, 2010

Make sure that no one stapled (or those white plastic straps with nails on either end) any wires to any studs and missed, driving a metal staple through the coax and the hot lines.
posted by deezil at 10:21 AM on March 2, 2010

If the coax is grounded at the head end, and your breakers aren't blowing, that pretty much rules out a short due to staples and whatnot. Far more likely is that the wiring to your basement outlets has been done on the cheap with two-wire ungrounded cable, and that the ground on the basement outlet is connected to the neutral on the basement outlet at the basement outlet - which is actually the hot side of the circuit, not the neutral side, because the cable is wired backwards.

You can eliminate the coax as the red herring it almost certainly is by plugging in a long, three-wire extension cord into the basement outlet, then taking the other end close enough to your genuine house ground to check for 120V between the extension cord ground and the real ground. Betcha you find it, and betcha it's solid enough to stay at 120V even if you load it with a light bulb.
posted by flabdablet at 2:37 PM on March 2, 2010

@flabdablet

That sounds like a really easy way to check out the ground on the outlet. I'll give that a shot as soon as I get home.
posted by PhillC at 3:32 PM on March 2, 2010

Try hard not to electrocute yourself. If you must electrocute yourself, make sure the current doesn't need to go through your heart - keeping one hand in your pocket is traditional good form.
posted by flabdablet at 6:01 PM on March 2, 2010

Go get yourself one of these. Then wander around the house and plug it into every outlet.

If I remember correctly, the right answer is two yellow lights. One yellow light is partial credit. Anything else, particularly if it involves a red light, is a fail.
posted by Kid Charlemagne at 8:26 PM on March 2, 2010

All that a tester like that can do is establish that the correct voltage relationship exists between the three pins of the outlet it's plugged into: mains voltage between hot and neutral, mains voltage between hot and earth, no or very little voltage between neutral and earth. It can't tell you whether both neutral and earth are actually at mains voltage with respect to the real ground (the one you walk about on, and the one the coax shield in this case is connected to). You need to do a direct voltage measurement between the real ground and the earth pin on the suspect outlet to find that out, and the easiest way to do that is with an extension cord.

But for Christ's sake be careful with that cord. Don't, for example, plug a toaster into it and then hold that in your hand while standing in the bath. If the basement outlet is in fact mis-wired, then the outer casing of anything "earthed" to it will in fact be at full mains voltage.
posted by flabdablet at 8:41 PM on March 2, 2010

@Kid Charlemagne:

That's exactly what I was using to test the outlet. I do get the "correct answer" of two yellow lights.

@flabdablet:

You're right, if that "ground" on the outlet is energized, then anything connected to it could also be energized. I will be sure to be extra careful.
posted by PhillC at 1:16 PM on March 3, 2010

Still with us, PhillC?
posted by flabdablet at 7:07 PM on March 6, 2010