getting false ground...

hello all,i have found alot of usefull info here,but here is my question,my home still has the old knob and tube wiring and my computer ups ground fault indicator lights up until i plug up the speakers to my computer which lead into a 4 switch selector for switching what i want playing threw the stereo like,computer,tv,xbox etc and as soon as i connect the video wire coming from the a/v converter for the tv the fault indicator goes off,so i know that this false reading is from the cable tv connected into the a/v converter as i can unhook the cable tv and the ground fault indicator comes back on,so my question is,is this a danger in anyway and could it possibly be helping me with a true ground or is it just a false reading and doesnt really mean anything as there is no true ground from the panel box…thanks for any info in advance…

Chances are somewhere in the layout you are getting a bootleg ground reading from one of the connections. In other words you may have the “grounded” conductor making a connection to the grounding connection somewhere in the setup.

I would place the entire circuit on a GFCI receptacle or breaker in your panel and re-look at all your equipment.

The cable TV wire conducts the wanted signal (TV) through the copper center conductor. In an effort to minimize interference from outside sources, the cable TV wire has a “shield”, a braided metallic conductor as a jacket, just under the black insulation of the cable. The shield and the inner conductor are separated by a white dielectric (non-conducting) plastic or plastic foam. Together, the inner conductor, dielectric, shield and black jacket are called CO-AXIAL cable, commonly shortened to “coax”. (Some coax does not have an exterior black jacket, usually when the “shield” is solid rather than braided. It is then known as “hardline”). When a cable TV installation is properly done, the shield is actually grounded at the point it enters the structure. This ground is usually connected to the same grounding point as the electrical system. Doing so, versus using a separate ground for the cable TV and the electric service is done to prevent “ground loops” which would induce voltage differentials between the ground points and the associated devices - an undesireable condition that could damage the equipment. (In a broadcast studio or at the transmitter site, EVERYTHING, transmitter, tower, electric, guy wires, telephone, transmitting and studio equipment, goes to a common ground point to eliminate any possibility of ground loops.) The grounded shield of the cable TV feedline is highly likely to be the point providing the “ground” in your situation.
My comments are based on information provided at an Ennis Continuing Education Seminar for Broadcast Engineers (former life occupation) on Effective and Safe Facility Grounding.

lol…translation ( by a Non-Engineer )…check your equipment, you are getting a bootleg ground somewhere and indeed it could be from the “shield”

The “Ground Fault” light on a UPS will light up when you have no ground present. That’s what it’s supposed to do. When you plug into a 2-wire (ungrounded) receptacle, you have no ground, thus the “ground fault” light. It’s doing it’s job. It’s telling you that you have no ground present (which you already knew).

When you connect the TV cable to the system, you’re essentially “backfeeding” the ground to all the connected equipment. The shield of the CATV is grounded at your service, and to the down ground at the pole where it starts. That’s why the “ground fault” light goes off.

If you were to have an electrician install a properly grounded receptacle for your UPS, the ground fault light will also extinguish. The short summary is YOU HAVE NO PROBLEM. Everything is doing exactly what one would expect would happen if you plug a UPS into an ungrounded receptacle, and it’s further doing exactly what I would expect to happen when you introduce equipment connected to properly installed and grounded CATV to the UPS.

(By the way, the surge suppression component of your UPS will not work until you plug it into a grounded receptacle. :slight_smile: )

I hope my response is clear, since this can be a complicated thing to get your head around. I’ll clarify if anyone is still fuzzy on any of this. I think this is an important thing to learn about.

I think I should clarify quickly. When I said, “YOU HAVE NO PROBLEM”, I mean that your home’s electrical system or cable television service has no problem. Everything is functioning just as it should.

The “real” problem is connecting equipment with a grounding type attachment cord (the UPS) to an ungrounded receptacle. That is the beginning and end of the real problem.

thanks for the responses,but the thing is dont i have some protection with my apc ups as the green light is lit up that says its protected wether its grounded or not,now i know its much more safer having the ground,no doubt about it but shouldnt it act as if it were like a gfci on an ungrounded circuit just as if you were to have a gfci breaker??? this one really has me confused here for some reason…and would the cable tv being hooked up to all my equipment really be a bootleg ground its not like tieing the neutral to the ground pin its just getting the ground threw everything connected in the selector switch and passing down to the ups,now i know its not like having a real ground as there is much more resistance as it has to go threw all these other connections and is not a thick gauge wire but shouldnt it give some help?? sorry i just dont see this as a bootleg ground as nothing was (tricked) to make the apc ups ground fault light go out…not trying to be confusing here but i work with electric on a daily basis but this one just has me a little bit in wonderland…lol…thanks to all those who have replied…david spain:cool: