Electrical problem in garage, short circuit?

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Hey all, I'm having a heck of a time trying to figure out what's going wrong with my wiring to my garage. I have a 1905 build house and a detached garage. The panel has been upgraded to 100amps and I have newer wiring running the length of the house to the back. There it runs through the foundation and into conduit where it runs underground using the grey underground rated wiring. It enters the garage and goes to a junction box and from there is distributed thorughout the garage.
Here's what's happening. The circuit breaker tripped (20amp) and I didn't realize it for a little. So I find it, and flip it back on. CLICK it immediately switches off. I flick it again CLICK same thing. Being a stubborn fool I throw it on again...VOILA! It stays on. So I went out and flicked on my garage lights and they flickered in and out dimly. I went ahead and turned them off and went back and thew the breaker off.
I know the issue is not the wiring in the garage after the initial junction box because I just rewired the whole entire thing (it needed it) and am getting the exact same response with the new wiring.
I've tracked the wiring from the panel to the junction box at the conduit outside the house and didn't find any apparent nicks or issues. This leads me to believe my issue is underground between the house and the garage. Now here comes the much awaited question...
How do I test the line to verify this??? Can I use a multimeter to do some tests on it? I'd really like to figure this out and if it means replacing the wire underground, so be it. Just want this resolved!
thanks! Brad
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You need to disconnect all the garage wiring at the point the direct burial cable enters the garage, from the feed cable. Next disconnect the cable in the house at the last accessible point before it goes underground. Now you have one length of cable with nothing connected at either end. Use a continuity tester and touch each wire and ground- there should be no connection. Then test between wires- again there should be no connection. If you get continuity between wires or from any wire to ground, you've got a bad cable

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RBM wrote:

You did not mention what range on the meter to use. I'd Rx10000(10K Ohm) use to make sure there is really no shorts.
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The simplest explanation is, you already figured out, a short in the cable between the house and the garage. Possibly it is an intermittent short, that is why sometimes the circuit break would stay on.
First disconnect everything in the garage from the junction box. Or, if you are so confident that nothing is wrong with the wiring in the garage, then just turn off everything in the garage.
Now, if you have an ammeter (30A range) or a clamp-type ammeter, measure the current from the house panel going into the cable to the garage. Normally there should be zero current because everything is disconnected (or off). If you see current, then there is a short somewhere.
If no ammeter, use a light bulb as if it is an ammeter. If the bulb lights up, then something is wrong.
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I don't have an ampmeter and I'm not sure exactly how I would use the lightbulb to do this. Can you expand on this for me?
You guys have been a great help so far and I am going to try all these methods tomorrow when there is sunlight again...since I have no garage light!!!
thanks! Brad
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Attach two wires to the light bulb and insert this between the main panel breaker and the black wire going to the garage. If there is a short circuit in the cable underground, then the bulb would light up.
Actually, this is better than using an ammeter because if there really is a short in the underground cable, an ammeter could be damaged, whereas the light bulb will be ok.
If the bulb stay dark for a few minutes, then perhaps there is no short circuit (or the short has temporarily disappeared).
In that case, leave the bulb in place and turn on a light in the garage. Pick a light with the same wattage as the one being used as a tester. If everything is normal, both bulbs would light up dimly since they are each getting only 60V.
Keep observing the bulb in the main panel. If it flickers between half bright and full bright, there is a short circuit somewhere. If it flickers between half bright and fully off, there is an open circuit somewhere.
If it flickers between full on and full off, you have both a short and an open circuit!
Use two low wattage bulbs, like 15W. This test is relatively safe (from causing anything to overheat) because the max current is limited to 130mA. Still, don't leave the test unattended until you found the problem.
If you're really unlucky, your problem may only show up when you draw higher current.
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Guys, a couple of points I haven't seen written here so far... First, if you ARE going to insert a light into the circuit, use a suitable fixture for this purpose. A keyless porcelain light fixture would probably suit the bill nicely and keep you safe for testing purposes.
Secondly, if you ARE going to continue with home wiring projects, you really should invest in an amprobe. MANY, MANY *home electricians* have house fires because they don't understand that just because it works, doesn't mean it's safe. An amprobe for example, will give you a good indication as to precisely how loaded the branch circuits in your home are. One useful opportunity for me is, every year we do the customary home decorating for Christmas. To protect our home, that's one of the final checks I do - an amp check on the branch circuits to ensure I'm not exceeding the capacity of that branch circuit JUST IN CASE any breakers were to fail in which case, I could conceivably be having heated wiring throughout my home which leads to fire. So again, if you like being a home handyman (and that's cool - there's nothing wrong with that), make the investment and pick up an amprobe to keep the house in one piece, family safe, etc etc...
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I probably would start by shutting off switches to everything and trying to reset the breaker from that point. (incidentally, it's a good idea to be standing in front of a panel when resetting breakers - turn your head the other way as well. When breakers literally blow and they do occasionally, they can make for bad news for the person doing the resetting. All that said, if the breaker held, I'd try slowly turning on and off switches to try and establish what part of the circuit is shorted (if you have a short at all).
How old is the run between the house and the garage and is the service grounded? Some of the older services aren't and that can lead to troubleshooting errors as well as potential safety hazards.
To test the feeders between the house and the garage, ideally both ends will be unwired so as not to backfeed anywhere - from there you can use a multimeter on the highest scale or better yet and more conclusively, a megger. However, assuming you've done nothing to disturb the underground feeders, the chances are probably better there's a junction box issue somewhere or a wiring error. Another meter that's been beneficial for me in the past is a digital amprobe that can be set to capture the inrush current when the breaker's reset. A shorted circuit can pull some pretty heavy amps until the breaker trips and my digital captures and holds the highest reading.
Also, after a single breaker has tripped, it should be viewed with skeptism in other words, don't assume it's okay because it passes power - might you have a bad breaker? If it seems stable, what's the voltage to ground off the discharge side of the breaker and how does that compare to other branch circuit voltages (using a digital versus analog voltmeter if you can - analogs like the old triplett can be so sensitive that you'll pick up phony readings where potential bum neutrals are concerned making for a troubleshooting nightmare. When I'm reading something that looks strange, I'll always use a second meter to verify the first meter readings.
Hope this helps...
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...
Actually, I'm glad you gave the warning.
I think the last few throws of the breaker did some serious damage, (the flickering and dim-out) and the garage breaker should NOT be turned on again until the problem is diagnosed.
The dimming means that the wiring is damaged, and is overheating.
I'd start with pulling the covers off every switch and outlet in the garage and inspect for burn marks and melted insulation. I don't care whether it's your new work or not, sometimes even professional electricians goof up.
If you find something, repair it, and retest.
If you don't find something, make sure that everything in the garage is turned off. Pull the hot wire off the panel breaker. Kill the main power. [May not be strictly necessary, but better safe than sorry]
Do a resistance (or continuity test) between the loose hot wire and the panel sheet metal or better still, the neutral going to the garage.
I'll bet you'll discover continuity or a relatively low resistance. Disconnect the hot wire at the first box in the garage. Test again. If still low, it's the feed wire. If not, retest the hot wire to the rest of the garage. Keep subdividing the circuit until you find the connection or wire segment that's got the short.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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On Mon, 14 Aug 2006 18:42:31 -0700, cover

Thank ( you fill in the blank - God? :-) that I caught my own error.
The line above was meant to indicate that UNDER NO CIRCUMSTANCES SHOULD YOU STAND DIRECTLY IN FRONT OF AN ELECTRICAL PANEL WHEN YOU RESET A TRIPPED BREAKER AND THEN, AS YOU STAND OFF TO THE SIDE, IF YOU MUST USE YOUR HAND TO RESET BECAUSE NOTHING ELSE WILL DO, TURN YOUR HEAD AWAY WHERE ANY RESULTANT FLASH OR EXPLOSION CANNOT INJURE YOUR FACE OR VISION.
Sorry I didn't get this accurate the first time, but the story stands as written above. Tripped breakers must be approached with extreme caution if you value life and limb... There's a tremendous amount of energy present in a short circuit and if everything goes right, the breaker trips, if not - the person doing the reset can get more than they bargained for...
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If you do find a short, I'd start digging right along side the house or the outside of the garage. Chances are the conduit has sheared because of the ground heaving and this is pinching the wires. A lot of the time dirt will pull away from a wall in dry times allowing water to run down along side of a structure during wetter times and when this freezes bad things happen.
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On Tue, 15 Aug 2006 02:53:57 GMT, "CraigT"

water. How many think this is true?

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Well, maybe not _all_ conduit, but a good majority of it.
Conduit is for physical protection. _Not_ for keeping the wire dry.
There is a specific layout you're supposed to use for burying wire (or conduit).
For example, the wire comes out of the wall, thru a conduit elbow, and goes straight down in conduit to the proper burial depth. This will tend to prevent freezing from damaging it.
Further, if you're doing direct burial (eg UF or NMWU), after the wire leaves the conduit (booted or plastic conduit) at depth, you're supposed to leave either a loop, or an exaggerated curve. Hence, expansion/contraction won't stretch the wire.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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If not full of water (which it may very well be), at least in a likely damp environment.
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On Tue, 15 Aug 2006 02:53:57 GMT, "CraigT"

You know, you might be onto something here with the ground heaving. If there were much in the way of trees in the area, it's a possibility that the conduit run suffered some root damage. Perhaps just enough to create the issue. Again though, disconnecting both ends and megging the feeders to ground would uncover such an issue. Good point on the heaving ground, I've recently had some tree root issues so can appreciate the damage tree roots can do.
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This is quite a bit like NASA saying, "We know the problem is not the insulating foam because we just redesigned it." You DON"T know the problem is not the wiring in the garage.
You think it's not. You've concluded it's not, but you don't know.
And I would say this to a pro, too, except I wouldn't have to.
Follow RBM's advice in the first reply you got.

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mm wrote:

I feel really sorry for people who does not think logically. Step by step, think logic.
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Reminds me of the furnace I repaired. The breaker tripped, so the woman of the house turned it back on. It tripped again, so she turned it back on. Finally after about ten resets, the breaker stayed on. But the furnace still wasn't running. What happened was that the blower motor shorted out. After resetting the breaker a few times (and a few major power surges through the furnace) the circuit board with the relay burnt out. Which created an open, not a short.
I suspect you had a short in the under ground wire. You power surged it enough times, now you burnt out something and now you have an open.
When the breaker trips, it means something is shorted out and needs to be repaired. Yes, you can test it with a VOM.
--

Christopher A. Young
You can\'t shout down a troll.
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Disconnect the wires at each end of your underground line. Then use your multimeter to check for continuity between each of the wires. There shouldn't be any reading between the hots and neutral, hots and ground, or neutral and ground. If you get a reading between any two wires, there's a short somewhere. If you've worked your way as far as you can go on each end, the short is probably in the underground cable and will need to be replaced.
However, before you start digging, remove the cable from cable clamps on each end and check again. I wired our house a couple of years ago, but the light circuit in my office would trip every time I turned on the light switch. The short was right at the ceiling box (metal for ceiling fan), where the cable passed through a cable clamp. I apparently tightened that clamp a little too much and it cut through the insulation causing a short to ground. I pulled the cable out, installed a piece of heat shrink tubing over each wire, and a final piece of heat shrink tubing over the entire cable. Reinstalled, used a little more care tightening the clamp, and everything works great.
Also, if you can't find a short in the cable, don't rule out a bad breaker. It's rare, but they can be defective. If everything comes up OK, replace the breaker.
Anthony
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Okay, I have isolated the issue and it IS under the ground as I suspected. I ended up running a new wire above ground from the house into the garage to see if it would work and it worked perfectly. Also, just to be sure, I powered the line going into the ground via another circuit branch to make sure it wasn't from the panel to the outside drop. Sure enough it had the same flickering issues.
So now I've got to determine if the cable can be saved at all...I'm pretty doubtful. The real kicker is that it runs under asphalt the whole way from the house to the garage.
Any tips on how to deal with this? Should I dig it up or just cut it off and put in a new run? It doesn't seem like it's a straight shot so I don't even know how I'd trace it without cutting up a ton of asphalt. If I stand in the back of the house and look straight at the garage, the wire enters the garage about 15 feet to the left. No telling if it's a straight shot, a "L", a "Z" or whatever.
My first thoughts are to put a diamond blade on a circular saw and cut a small trench 3-4 inches and then dig it out to 12+ inches and lay conduit the whole way and then backfill. Suggestions on this logic?
thanks!
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