Ground Short


Old 10-11-03, 10:59 AM
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Ground Short

This is long since I'm somewhat inexperienced.
I have a pair of ouside lights that keep blowing the circuit. I've narrowed it down to a 3-wire line running from the left light to the right. On the left side if I disconnect the black, white and ground going to the right the circuit stays up OK. REAL basic question, when I use a continuity tester on the wire i've disconnected, i.e. the wire that runs from the left light to power the right, black to ground shows continuity (which I don't think it should), white to the ground wire is open. On the main wire that runs to the house white and ground show continuity which is right no? From peering into the circuit box I looks like all white wires and ground wires connect into the same bus. White is usually referred to neutral right? Neutral and ground should be connected, right? This wire that goes between the two fixtures, when fully disconnected from everything, there should be no connectivity between any pair right? I am thinking that somehow the black wire is shorted to the ground wire on this piece. If I reconnect the black and white wires but leave the ground disconnected both lights will work and circuit breakers are all staying ok. Have I correctly diagnosed that this short wire that goes between the two lights is the culprit? I can connect one of the lights cleanly, black, white and ground all is OK. What risk am I taking hooking up the other with just black and white and no ground? Replacing the wire would mean tearing up the driveway.
The lights themselves are mounted to a plastic tube that is set in a mortar and stone thing at the end of the driveway, not a metal post. Any advice is highly appreciated. THANKS.
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Old 10-11-03, 06:29 PM
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Location: welland ontario
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Open up the light that is on the other end of the line with the short. Note the connections and disconnect the cable. You should now have nothing connected at both ends of the cable . Do a continuity test again. If you get any continuity then the cable has gone bad. Perhaps someone pounded a nail or screw into the line somewhere.
Old 10-11-03, 08:43 PM
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Thanks Joed. I did disconnect the lights altogether. The cable between the lights is bad. I hooked up one light with ground, the other without and all's well. The short cable, the one running between the lights, apparently has some problem probably critter related. I merely hooked up the black and white parts of the wire to each other and left the ground connection going to the other light disconnected. I can't see very far down where the wire goes but I guess the problem is exactly what you said. Light works fine with no ground and it's not in a place where one would have any reason to touch it so I guess I got out of this one cheap.
Old 10-11-03, 09:41 PM
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You mentioned that you confirmed continuity between hot and ground on the wire in question. That being said, your "fix" has created a situation where voltage exists on the ground wire. It's not connceted to anything, so it won't trip the breaker. But it's still there, in the ground and, in the boxes and fixtures. Lets just say I wouldn't want to be the guy that stuck my hand in that J box for maintenace reasons, or grabbed the frame of the second light fixture for any reason. What you have done is dangerous and should be undone promptly.
Old 10-12-03, 07:30 AM
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Hi CSelectric,

I'm confused. The main power wire leads from the house, underground to the first light fixture. The first light fixture is wired properly, to the ground wire. The "bad" wire leads from the good light to the light on the other side. This bad wire is where I have the problem. With the bad wire totally isolated I get continuity between the black wire and the ground wire. What I did was just not connect the ground wire from the bad to the ground wire from the bad. So now one lamp is grounded, the other is just connected via the black and white wire, that fixture is not grounded at this point. I realize this isn't correct. I will essentially put a note on the box in the basement detailing this in case anyone is called in. I'm attempting to figure out a way to run a new wire without digging up the driveway. The lamp in question can only be access by climbing up a stone wall and then up more to yjr lamp itself. It cannot be reached from the ground. There is no J-box outside and the two lights are 20~25ft away from each other. This unconnected ground wire has been throughly taped on both ends, it can't touch anything metal anywhere as ecerything is plastic and stone. This all being said, I'm gonna disconnect the lamp today and figure out a way to run a new line.
Old 10-12-03, 07:41 AM
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Ok, thenthe question is, how does that undeground run get up the wall?

My point was, if you have continuity betwen the hot and ground in the underground run, then you will have voltage on that ground wire when the lights are on. If it is disconnected from the ground wire running from the panel (at the first fixture) then you have opened the fault current path, thus preventing the breaker from tripping. You have not, however, eliminated the short between the hot wire and ground wire in the underground. Thus voltage will still exist on the ground wire in that section whenever voltage exists on the hot wire. Yes you have the wire in question isolated, and you've taped the bare leads to isolate them in the box. But, does the next guy who changes a light bulb or otherwise works on that system know that?

Just for reference, disconnect that second cable run again. Now, push a long screwdriver into the ground and check for continuity between the hot and the screwdriver blade. I suspect you will find that the short is not exclusively between the hot and ground wire, but also between the hot and earth. (incidentally, if you are usuing a continuity tester, this may not work. A multi meter with auto ranging ohm function is what is required. If you have one, give it a try.)
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