Thread: Ground Loop
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Bob Simon[_2_] Bob Simon[_2_] is offline
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Default Ground Loop

On Sunday, October 27, 2019 at 8:02:04 AM UTC-5, Scott Dorsey wrote:
Bob Simon wrote:
My Panasonic TV (TH-50PH9UK) is a video monitor only; all audio is routed t=
hrough my NAD preamp and amp. Last week, a hum started without having made=
any changes to any systems. Today, I tried unsuccessfully to eliminated i=
t by plugging the TV into the same power strip that the preamp and amp are =
plugged into. Lifting the TV's ground eliminated the hum.


The TV has multiple grounds. That's the problem. Likely what you mean is
"lifting the TV's power line safety ground."

Does this suggest that a capacitor shorted last week in the amp, preamp, or=
TV?


No, it suggests that the grounding system on the cable TV line has likely
changed, since this is the most common source of these problems.

As a practical matter, have I created an unsafe or inappropriate condition =
by lifting the TV's ground pin?


Yes, totally. They don't call it a "safety ground" for nothing. Isolate
the ground on the cable TV line, not on the power line.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."


Scott,
Thank you for your reply. Yes, I lifted the TV's safety ground.

The cable demarc is attached to the garage and is around 50' from the grounding rod for the electrical panel. The demarc has a separate grounding rod connected by some thin wire (perhaps 16 AWG). If I ground the demarc with 10 AWG solid copper wire and a brand new clamp, will that likely eliminate the multiple grounds issue?

I bought the Jensen ISOMAX years ago because I was told it would eliminate the cable ground issue. Apparently, it isn't. Do you have any idea why not?
Bob