Newsgroups: misc.industry.utilities.electric,sci.engr.electrical.compliance,sci.engr.electrical.sys-protection,alt.home.repair
Subject: Re: VERY bizarre grounding problem
References: <[email protected]>
Adam Smith  writes:
> I have a surge protector with a "site wiring fault" light built-in. It
> indicates grounding and polarity problems. One day, I noticed the light
> was lit. It had been used for about two years in the same location and
> on the same circuit, so I considered it to be rather odd that this light
> would suddenly come on. I came back a few hours later, and it was off. I
> turned the surge protector off and back on, and the light immediately
> came on when I turned it back on.
> 
> I assumed the surge protector was at fault, so I purchased a new one.
> This one has a "grounding" light, which is similar to the "wiring fault"
> light, except this one is supposed to normally be on. I turned it on at
> first, and voila! The grounding light was on. 15 minutes later, it shut
> off. I turned the strip off and on, and it flickered and turned off
> again. I ran it for awhile, and it suddenly glowed dimly.

You should definately check the grounding of your power outlet.
Get an electrician to check the wiring and correct the problem.
You propably have a bad ground connection.
 
> THEN, I just happened to reconnect a disconnected coax TV cable. The
> grounding light immediately came on. I repeated this several times, and
> it seems to get a ground through the coax TV cable.

The shield of the coaxial cable is grounded, so when you connect it
to your PC your PC gets grounded through it. This will make simple
ground testing circuits happy, but is not a a proper safety ground.
 
> Neither of these surge protectors had direct coax inputs. However, they
> were both connected to my computer, which has a television card. 

In typical TV cards I have seen the shield of the coaxial cable input
connector is directly connected to PC case, so when you connect a
grounded coaxial cable to PC, the PC case gets grounded through it.

> I did
> not always have this card in my computer, so I know the surge protector
> wasn't always dependent on the cable for grounding.

It is possible that some wire has gone loose on the power outlet or
somewhere else in the electrical installation system. It might have worked
well nicely before, but then something in wiring has oved and connection
is not good anymore.
 
> Strange, huh? The grounding problem doesn't seem to come and go with any
> particular appliance, but then again I can't tell what all in my house
> is on and off at any given moment.. The coax cable is split and goes
> into my receiver, and I noticed that the stereo gets a significant
> amount of hum when a TV in another room is on, but this on/off grounding
> problem doesn't seem to be correlated with the operation of the TV.
> 
> There is some remodeling going on in another room (some outlets ARE on
> the same circuit), but nothing has been modified electrically and it
> wouldn't explain why the problem is intermittent.

THe remodeling might have moved the wires in conduit in in some
way and some already bard connection had gotter worse. That's my
quess.

> Please e-mail me about this. I'd like to know if I should be concerned,
> and what I might do to remedy this problem. The idea of my surge
> protector rerouting a lightning strike through my TV cabling doesn't
> strike me as appealing. ;)

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web pages at http://www.hut.fi/Misc/Electronics/