Fried tuner...how can I tell if my CATV cable is properly grounded?

[Ichinisan]

I recently purchased an eVGA/NVIDIA NVTV dual tuner card for use in my MCE2005 rig. It fried shortly after I had everything set up, even though it was running through a brand-new surge supressor of decent quality (with a grounding indicator, probably relating to the electrical socket) and there had been no bad weather. When I touch the coaxial connector and the case chassis at the same time, I can feel an uncomfortable amount of electricity flowing through me and shocking me each time my tender arm gets near the chassis. :Q

Do surge supressors use the ground from the electrical socket for the coaxial cable? It would make sense.

As a cable Internet installer for a different cable company, I went out to the box on the side of my house to have a look and saw that the splitwork was not grounded. The cable technician looked at the utility pole where the wire is coming from and says that the cable is grounded there. How can I tell if the ground is actually working? If it is, shouldn't the charge be equal to that of my electrical ground, causing little or no electricity to flow when I touch the chassis?

 

[Ichinisan]

^

 

[Navid]

Don't touch it with your hand!
Do you have a volt meter?
If you do, set it to AC Volt and measure the voltage between the two grounds. It should be Zero. But, it won't be based on your experience (shock).
What is the voltage? This may give you a clue.

 

[TwoBills]

Using a vom, set it to 100,000 ohms. Disconnect the cable from your modem. Put one lead on the outside of the cable fitting and the other lead to a known ground (receptical screw or the semi round hole in the receptical). You should get a reading on the meter. No reading, no ground.

 

[Navid]

Originally posted by: TwoBills
Using a vom, set it to 100,000 ohms. Disconnect the cable from your modem. Put one lead on the outside of the cable fitting and the other lead to a known ground (receptical screw or the semi round hole in the receptical). You should get a reading on the meter. No reading, no ground.

I wouldn't do that yet!
If there is voltage on the wire you are testing with the Ohm meter, you can damage the meter.
I would measure voltage as the first step.

 

[tiap]

You shouldn't feel anything when doing that, no matter how sensitive you are. Basically, you are completing a circuit.
Sounds like you are somehow acting as a conductor.
Start by checking the wall plug for proper ground, then supressor, then psu etc.
NEC requires that your cable be grounded at entrance to your house, usually to a ground rod or water pipe (hose bib)

Some electricians like to be creative and start swapping neutrals and grounds instead of running extra wires without knowing the full impact.

 

[Ichinisan]

The building is a barn which was just recently wired by myself and my family. Even though I had never done electrical wiring in the past, I am confident that it was done properly. It was inspected by certified inspectors several times before and after it was completed. The grounding rod is outside by the service disconnect switch. My surge supressor indicates that ground is functioning properly with it's "SurgeStat Indicator".

http://www.rca.com/product/viewdetail/0,2588,PI700875-CI123,00.html?

I will try the volt then ohm tests when I get home.

 

[TwoBills]

Originally posted by: Navid

Originally posted by: TwoBills
Using a vom, set it to 100,000 ohms. Disconnect the cable from your modem. Put one lead on the outside of the cable fitting and the other lead to a known ground (receptical screw or the semi round hole in the receptical). You should get a reading on the meter. No reading, no ground.

I wouldn't do that yet!
If there is voltage on the wire you are testing with the Ohm meter, you can damage the meter.
I would measure voltage as the first step.

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That's true, but the chances of ac voltage on a cable connection, enough to do you or the meter any damage, are so remote that I don't even consider it. Besides, if the problem is lack of grounds, then you won't get a voltage reading, even if there is voltage there.
I'd just pull the sucker off and check for ground.

 

[Navid]

He has been shocked!
That means voltage.

If what you are saying is right and there is no voltage, measuring the voltage first is not going to cause any problem except losing 30 seconds of time!

If what I am saying is right and there is voltage, doing what you suggest risks damage to the meter.

 

[Ichinisan]

To be clear, it doesn't feel like being shocked from an AC outlet, but it's definitely noticeable and uncomfortable. It's weak enough that you might not notice the feeling of current flowing through you, but I can feel the shock each time my arm gets close to the chassis or pulls away from it. It's pretty annoying if you're resting your arm on the chassis and you feel the tiny shocks over and over.

 

[TwoBills]

Originally posted by: Navid
He has been shocked!
That means voltage.

If what you are saying is right and there is no voltage, measuring the voltage first is not going to cause any problem except losing 30 seconds of time!

If what I am saying is right and there is voltage, doing what you suggest risks damage to the meter.

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We were talking about coax and lack of ground. Can't read voltage w/o ground. Any little bit of voltage on the coax would just "ping" the meter a little anyway.

After the OP's last post it sounds like he's got a house ground problem. Need to stick the meter lead on the case and see what's tinglin'.

 

[imported_tonka]

Originally posted by: TwoBills
Using a vom, set it to 100,000 ohms. Disconnect the cable from your modem. Put one lead on the outside of the cable fitting and the other lead to a known ground (receptical screw or the semi round hole in the receptical). You should get a reading on the meter. No reading, no ground.

My cable drop runs underground from a pedestal on the street. l have it grounded to a 3 foot earth rod which is not bonded to the main electric service ground.

I tried what you said and I got a reading of 52.x -- does that mean my ground is ok?

Incidently Dish network was installed by "pros" and is only grounded to the short aluminum pole they installed to hold the dish. It is not bonded to the main service either.

I assume all the above works no matter what the NEC says. Right?

 

[CrispyFried]

You may have a ground loop, ie grounds at different potentials. Shouldnt happen but it does. Ideally all grounds should goto the same place.

I dont think 3 feet is long enough for a proper ground rod. I thought 6 feet was minimum, but Im not too sure.

 

[bendixG15]

3 feet is in the real world, code may say 6 ft.

 

[CrispyFried]

"Real world" may cover 95% of the situations. But code is there to cover 100%

 

[TwoBills]

Originally posted by: tonka

Originally posted by: TwoBills
Using a vom, set it to 100,000 ohms. Disconnect the cable from your modem. Put one lead on the outside of the cable fitting and the other lead to a known ground (receptical screw or the semi round hole in the receptical). You should get a reading on the meter. No reading, no ground.

My cable drop runs underground from a pedestal on the street. l have it grounded to a 3 foot earth rod which is not bonded to the main electric service ground.

I tried what you said and I got a reading of 52.x -- does that mean my ground is ok?

Incidently Dish network was installed by "pros" and is only grounded to the short aluminum pole they installed to hold the dish. It is not bonded to the main service either.

I assume all the above works no matter what the NEC says. Right?

Now drop that meter down to 1x or 10x and read it again. 100Kx gives you a minimum ground reading. Readings at 1 or 10x indicate a solid ground.

 

[The Boston Dangler]

The cable drop should (MUST) be grounded at the point of demarkation. That's the point where the cable cos. property stops and yours starts. Usually, if you follow the drop from where it hits the house, down to belt level, there will be a ground block (a splitter also works). From the ground block, you'll have a beefy copper wire going to a ground rod (code is 6 ft.), an electrical ground on the meter or panel, or a COLD water pipe. Hot water pipes are not reliable grounds.

In an apartment, the cable must be grounded in the lockbox. Usually, grounding the tap will be fine.

 

[imported_tonka]

[/quote]
Now drop that meter down to 1x or 10x and read it again. 100Kx gives you a minimum ground reading. Readings at 1 or 10x indicate a solid ground.
[/quote]

TwoBills, I got a little confused what the resistance setting should be so I took a reading at all available settings and they are as follows:

20M = 6.9
2M = .694
200K = 70.4
20K = 8.21
2K = .060
200 = 51.0

So do I have a solid ground?

 

[TwoBills]

Originally posted by: tonka

Now drop that meter down to 1x or 10x and read it again. 100Kx gives you a minimum ground reading. Readings at 1 or 10x indicate a solid ground.
[/quote]

TwoBills, I got a little confused what the resistance setting should be so I took a reading at all available settings and they are as follows:

20M = 6.9
2M = .694
200K = 70.4
20K = 8.21
2K = .060
200 = 51.0

So do I have a solid ground?

[/quote]

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Yeah, looks like it. Basically, the lower the scale on the meter, the more solid the ground. I'm usually looking for grounds that don't belong on a circuit. I start low and work my way up the scale to be sure there's nothing there. Kinda hard to explain, for me anyway. But I'd say you're OK.

 

[CZroe]

Well, Ichinisan just got his replacement tuner from Newegg today. The cable guy came out and said that it was all grounded "elsewhere" (Not at the box outside our house but at the pole). So I'm just hoping we don't fry this one with the same line voltage.