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Old 11-18-2008, 09:10 PM   #16
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GFCI Trips


I think you should do a few things a little less complicated before doing ohms tests. The idea to find a fault is to divide and locate. You have 3 outside receptacles connected to the load side of the gfci as I understand things on the branch that is causing the problem. This means you have another junction in another box somewhere in one of those other boxes and you may have one or two cables leaving that box besides the supply cable from the gfci box. You need to disconnect those from the receptacle and keep the wires isolated in wire nuts if possible just don't let bare of the wire touch themselves or metal. This gets the other two receptacles and wiring disconnected from the gfci load protection. So now you just have the gfci and one outside receptacle connected. See if the gfci holds with just that one receptacle connected. If it doesn't then the problem is between the gfci and that one receptacle.
Now if you don't have a trip out turn off the power reconnect a cable or one of the cables to the receptacle. Now you have the next branch connected to the receptacle and to the gfci. Turn power back on and see if it trips out. If no then connect the last outlet in the same manner careful to remember to turn off power and test for power to be sure at the outlet.

See where I'm going?
Isolate the branches of wiring on the load side of the gfci where the fault lies then you only have to look at that one branch. One of the branches when connected back to the protection of the gfci is going to show the fault and you have narrowed down your search.


Last edited by Stubbie; 11-18-2008 at 09:49 PM.
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Old 11-18-2008, 09:18 PM   #17
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GFCI Trips


Will recheck at 200k, but I had numbers bouncing all over the place at 20 k when I tried this.

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Originally Posted by Yoyizit View Post
Good. Everything is unplugged or switched off on this line, right?
You should read infinity (OL ?) from the hot cable lead to ground, same as if the leads were not touching.
I'd put it on the 200k ohms range, to start with.

If it reads infinity, or substantially more than 30k, the next step is the homebuilt "megger."
If it passes the megger test also then the problem is very likely not in the cable.
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Old 11-18-2008, 09:27 PM   #18
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GFCI Trips


Of course! Somehow that never registered in my electronically challenged brain.

Correct, there are a total 3 outdoor outlets (1 front porch, 1 back porch, 1 in the middle of the back of the house) "downstream" from this GFCI.

Your post makes perfect sense, and I will try as soon as I get some daylight. Anything in particular I should be on the lookout for in these outside outlets that causes common faults but mught not be obvious to the untrained eye?


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Originally Posted by Stubbie View Post
I think you should do a few things a little less complicated before doing ohms tests. The idea to find a fault is to divide and locate. You have 3 outside receptacles connected to the load side of the gfci as I understand things on the branch that is causing the problem. This means you have another junction in another box somewhere in one of those other boxes and you may have one or two cables leaving that box besides the supply cable from the gfci box. You need to disconnect those from the receptacle and keep the wires isolated in wire nuts if possible just don't let bare of the wire touch themselves or metal. This gets the other two receptacles and wiring disconnected from the gfci load protection. So now you just have the gfci and one outside receptacle connected. See if the gfci holds with just that one receptacle connected. If it doesn't then the problem is between the gfci and that one receptacle.
Now if you don't have a trip out turn off the power reconnect a cable or one of the cables to the receptacle. Now you have the next branch connected to the receptacle and to the gfci. Turn power back on and see if it trips out. If yes then connect the last outlet in the same manner careful to remember to turn off power and test for power to be sure at the outlet.

See where I'm going?
Isolate the branches of wiring on the load side of the gfci where the fault lies then you only have to look at that one branch. One of the branches when connected back to the protection of the gfci is going to show the fault and you have narrowed down your search.
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Old 11-18-2008, 09:47 PM   #19
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Just wanted to thank both of your for your help. It's been a long and frustrating couple of days, and I'm going to try to get some sleep (just don't want you to post more tonight and wonder why I don't respond). Aside from a brief appointment, I'm off all day tomorrow. Plan on spending all of the daylight on this problem. Will check back throug hthe day and keep you posted on my progress (or lack thereof).
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Old 11-18-2008, 10:36 PM   #20
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When you isolate the branch that has the problem remove the receptacle and keep all wires separated go back where you disconnected it and reconnect it to the gfci circuit this will tell you if it is the receptacle. If the gfci does not hold then it is a wiring problem. Something like a driven nail piercing the cable somewhere.

Heres the concept..... gfci's measure the current in the black wire (hot) and the white wire (neutral) (tell us if any red wires are in any of the boxes). If there is 5 amps flowing thru the black then there must be 5 amps in the neutral with a 4 milliamp or so tolerance. If the gfci sees 5 amps in the black but only 4 amps in the white it trips. This means that 1 amp is leaking to ground. Think of it like this... the amps flow out of the load side of the gfci on the black wire and return to the gfci on the white. The gfci must see this as being equal. If not then it trips. If nothing is plugged into any of the outlets then current cannot flow under normal conditions and the gfci just sees zero amps in both the black and white. Without something plugged in and turned on the circuit cannot be completed from the black wire to the white wire unless a hot wire has made a bridge by milliamps fault (small leakage of current) to the ground either at the receptacle or somewhere in the wiring. Lots of times water can accumulate on a receptacle and will allow current to flow from the black to the ground so you get the idea I think. Only the ground is not monitored by the gfci. How the gfci sees the problem is like this... if current is leaving the black wire to the bare ground wire somewhere on the load side of the gfci this current must flow thru the gfci on the black hot wire It is returning on the ground wire (not the white which is monitored by the gfci). So the gfci sees current on the black but nothing on the white and trips. Hope that makes sense.

So your gfci is tripping without anything plugged into the protected side of the gfci. This almost has to be a leakage of current from the black hot wire to bare ground. Also if your boxes are metal they are connected to the bare ground so leakage to metal can also cause the gfci to trip. Now this current loss to ground must be very very small. If not and the current loss exceeds the circuit breaker rating by large amounts the circuit breaker for the branch circuit the gfci is on will trip.

If you want a quick way to see if this is the problem disconnect all the grounds at the gfci with all the outlets connected to it correctly. Energize the circuit and the gfci will hold. This is because you have broken the return path and current cannot flow.....there isn't a complete circuit anymore. Without current flow the gfci senses no amps on the black wire even though it is leaking current to ground. Once you reconnect the bare grounds the fault returns and the gfci trips.

Last edited by Stubbie; 11-18-2008 at 11:36 PM.
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Old 11-19-2008, 10:08 AM   #21
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Here are a couple diagrams to assist you in understanding how your gfci works. I put three receptacles protected by the gfci to relate to your situation. The diagrams depict no loads (things plugged in) being operated from the receptacles. Bear in mind that it is possible for current to be leaking to both neutral and ground from water contamination. However the ground is not monitored and essentially is the root cause of the trip of a gfci in this situation. If the current was only leaking to neutral then both hot and neutral would be equal as far as the gfci is concerned and the gfci would hold all things being perfect.
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Last edited by Stubbie; 11-19-2008 at 05:29 PM.
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Old 11-19-2008, 06:32 PM   #22
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Fixed!!!!

Thanks for all the help. Here's what I did. I took apart all downstream outlets and figured our which was thge end of the run. That outlet (right above my AC units, which is never used) also looked suspect to me somehow. Can't say what, just looked "wrong." Went to lowers and picked up 4 new vanilla outlets ( 2 bucks a pop). Started with the suspect outlet. Whoever installed it used those stab holes in the back. When I tried to pull them out to check the condition oif the wires I couldn't get them to pull out. Seemed kind of strange. I snipped the wires, stripped off just enough to make a good curl and wrap it around the screws of a new outlet. Went to the garage and checked it out and voila! Power!!

Put all the others back together (with a healthy dose of silicone to keep future moisture out) and I was good as gold.

Just wanted to thank you again for the help. Sometimes the answer is right in front of you, but you just don't see it. Anyway, I don't use that outlet, and would like to put up some motion-detecting floodlights out back using those wires, although I won't be tinkering with wires till after thanksgiving at least. When I'm ready, I know who to check with. You guys are great!

Slainte!
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Quote:
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Here are a couple diagrams to assist you in understanding how your gfci works. I put three receptacles protected by the gfci to relate to your situation. The diagrams depict no loads (things plugged in) being operated from the receptacles. Bear in mind that it is possible for current to be leaking to both neutral and ground from water contamination. However the ground is not monitored and essentially is the root cause of the trip of a gfci in this situation. If the current was only leaking to neutral then both hot and neutral would be equal as far as the gfci is concerned and the gfci would hold all things being perfect.
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Old 11-19-2008, 06:45 PM   #23
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Congradulations....always nice to hear back that a problem has been fixed....
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Old 11-19-2008, 09:02 PM   #24
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Had to report back, you were a great help!

Still, I am a little irritated that I don't understand my multimeter yet. Weird, I've googled the heck out of it and still don't understand all its features (or even most of its features). Can you recommend a site or a book or something? Everything I've seen seem to skirt around the issue like it is some secret electrician's code or something. Even the instructions that came with the thing are kind of cryptic. Just hate owning any piece of equipment and not really understanding it.

Thanks!



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Congradulations....always nice to hear back that a problem has been fixed....
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Old 11-19-2008, 10:38 PM   #25
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Is it a digital meter?
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Old 11-19-2008, 10:55 PM   #26
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Was it leakage within a duplex outlet? Due to moisture?
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Old 11-20-2008, 05:25 PM   #27
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Digital meter, yes.

Not sure of the cause, but I would guess it was some type of moisture making its was in the outdoor outlet.
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Old 11-20-2008, 05:45 PM   #28
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Digital meters are not the best for house wiring but do have there place. They are more commonly used in the electronic field. However most electricians carry one for one reason or another. A anaolg multimeter is better. Digital meters are high impedance (unless labeled otherwise) and cause a lot of wandering readings when testing house wiring. Ghost or phantom voltages are a distraction when using these type meters and can be easily misinterpreted by the unknowing.

I'm not sure of a good site to give a tutorial on using a digital.. might try googling 'instructions for digital multimeter' or other search keywords.
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Old 11-21-2008, 04:06 PM   #29
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Roger, thanks

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