What Else Can I Check with A Tripping Breaker?

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Old 12-01-17, 09:08 AM
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What Else Can I Check with A Tripping Breaker?

I have two pier outdoor lights that when turned on, the breaker trips. I know electrical fairly well, but lack experience, so I need some suggestions on what it could be.

* The breaker trips only when the pier lights are turned on; if they are off it never trips.
* The breaker trips from 5 minutes - 3 hours after turning the lights on.
* The breaker trips while all other lights are off that are part of the same circuit.
* There were no changes to the fixtures/wiring for a year; this just happened out of the blue.
* I checked the wiring in the junction box and at the outdoor lights and everything is tight.
* The breaker trips even if light bulbs are in just one of the lights (or the other).
* The breaker trips after changing the light switch.
* The breaker trips using either LED or incandescent bulbs.
* The circuit is not overloaded, the breaker trips even with just one light bulb in the entire circuit.
* I switched the breaker with a known good one and still trips.

This circuit has only 3 lights to it (pier lights, porch lights, and foyer lights). One year ago I added a convenience outlet to the circuit, but the breaker trips even when nothing is plugged into the 1-year old outlet ...and the breaker only trips when the pier lights are on, so again, I went a year with no changes and no tripping.

Today, I will be disconnecting (un-wiring) one pier light, and then the other to see if there's a trip, but I'm gonna guess it trips with either one since removing light bulbs is kind of the same thing.

Thanks!!
 

Last edited by tony17112acst; 12-01-17 at 09:36 AM.
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Old 12-01-17, 09:38 AM
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There is something wrong in the pier lights. Being it takes at least 5 minutes for the breaker to trip, my guess is at least one pier lamp socket is heating up when the lamps are ON and shorting the hot lead to the neutral lead. You can find the bad socket(s) by only having one bulb powered in the string at a time. If the breaker doesn't trip after 3 hours, move the bulb to the next lamp socket. What is the tripping breaker rating? Are the lamps the correct wattage for the sockets?
 
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Old 12-01-17, 09:41 AM
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Bob...he tried that...look at his sixth symptom/step.
 
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Old 12-01-17, 09:49 AM
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My guess is something wrong with the wiring in or feeding the pier light fixtures. Probably a small break in a wire that is collecting moisture. If the wiring goes underground at any point, that's a likely spot. Rodent damage would be another item high on my list. Perhaps something that could shift around like a sharp edge of metal siding or a box clamp too tight.
 
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Old 12-01-17, 10:13 AM
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I'm with Ben. If it takes a while for the breaker to trip..... it's an underground problem. The time it takes to trip is dependent on how wet the earth is around the fault.

An ohmmeter will probably be needed for diagnosing the problem.
 
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Old 12-01-17, 10:32 AM
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The wiring is indeed underground, and it's about 80 ft! How would I verify that there is an underground fault? With an Ohmmeter?

I just thought of another test. What if I hooked up a different cord (hard-wire an extension cord or something on a dry day) directly from the switch to the pier. If there's no tripping, it's the underground cable, and if it trips, then it's the lamps. Any flaw in that test/conclusion?

FYI, when I reset the breaker, sometimes it trips 60 minutes later, and sometimes immediately. If it were moisture, would it trip that long after I reset it?
 
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Old 12-01-17, 10:38 AM
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That's a reasonable test with the extension cord or NM cable rolled out on the grass. A bad break in the wire will show on an ohmeter as positive resistance between hot and ground with both ends of the cable disconnected. That measurement should be infinite (which most meters show as exactly zero). A tiny break will probably only show using a professional meter called a meggar.
 
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Old 12-01-17, 11:52 AM
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To Gunguy45:
OP didn’t say he moved the lamp from socket to socket in the string. In troubleshooting maybe he got lucky and used the faulty socket the first try. It can also be the last socket he tries in the string. If the underground wire is the problem, the breaker should trip with no lamps in the powered string.
 
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Old 12-01-17, 12:03 PM
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OK, that's a new test I can try right away ...remove all bulbs and turn on the switch. I'll report back in an hour or so to give an update on that test.

FYI, there are 3 bulb sockets for each of the two piers (total = 6). I will also try one bulb in each of the 6 sockets later tonight and report back those results too.

What about testing for continuity by twisting the hot and ground wire together at the light, then checking for continuity at the switch (with no juice, of course). I don't know if my very basic digital mulimeter does continuity that far (150+ ft.).
 
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Old 12-01-17, 12:10 PM
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Also FYI: I did try just one bulb in each one of the two piers alone, so it tripped with either one ...I think that means BOTH light fixtures in the piers would have to be defective ...which is improbable - I'm thinking.

I also just realized, a continuity test would test OK since I get lights on for an hour or so.
 
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Old 12-01-17, 12:54 PM
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did I miss the failure mode?
Is it ground fault, load current fault or arc fault?

a 15 or 20Amp load fault repeated trip will leave some evidence.
 
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Old 12-01-17, 01:20 PM
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telcomguy: I'm not sure what fault it is yet, unless I'm not understanding your post.

It's a 15 amp breaker and all my tests where it trips has every item on the branch turned off - so the only item with juice is the light itself.

What do you mean by "a 15 or 20Amp load fault repeated trip will leave some evidence." ...could you expand?

Thanks for everyone's time so far!!
 
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Old 12-01-17, 01:28 PM
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A ground fault is when a hot wire directly contacts a ground wire or grounded metal surface. The evidence this type of fault leaves is burn marks or divots of blown out metal. You can see and hear a spark and whiff of smoke if you're nearby when it happens.
 
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Old 12-01-17, 02:13 PM
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New test result:

OK, the breaker just tripped with no light bulbs in any lights - with the light switch on.

What's my next move?

What if I disconnect the two light fixtures and turned on the switch? If it doesn't trip then it's the fixtures. If it does trip, the fault would be in the underground wire (or coincidentally both the underground wire and the fixtures) ...right?

The fixture look to be original (1976) and there's a lot of bug guts and stuff in there too.
 
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Old 12-01-17, 02:17 PM
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Disconnect one fixture at a time, That way you can narrow down where the problem is.
 
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Old 12-01-17, 02:31 PM
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So, I take it this is not a GFCI trip? You can now remove ONLY the neutral wire to see if the fault is hot to neutral. If the breaker still trips, you are looking at a hot to ground issue.

But, this would take some box work at the panel. Not sure of your experience level.
 
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Old 12-01-17, 04:16 PM
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You have a two wire cable with ground between the house and the pier. You need to isolate both ends so it's not connected to anything. Then using an ohmmeter you need to check between all the pairs. Black, white and ground. There should be no meter movement during this test. More than likely you will see resistance between the black wire and ground. That would explain the delay in the breaker tripping,
 
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Old 12-01-17, 05:41 PM
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pugsl: I"ll do that tomorrow morning and report back (hoping its the fixture and not underground wire).

telcomguy: No, this is a standard breaker. I have decent knowledge as I have done a few service panels that passed code.

Pjmax: Yes, it's 14/2 wire. I'll do this after my remove-fixtures-test because there is a LOT of gang box work as there are 8 romex's (2 are 12/3) in a 4-gang box, and all of the neutrals are mashed together ...it's a nightmare. I'll try hot and ground in the morning before tearing the whole thing apart to test the neutrals.

I'll report back tomorrow with more info ....THANKS FOR ALL THE ADVICE!
 
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Old 12-01-17, 05:51 PM
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The neutrals of a #14 circuit should not be connected with the neutrals of a #12 circuit. Neutrals need to be kept separated according to their circuits. Grounds get tied together.
 
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Old 12-03-17, 11:57 AM
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New Test Results

After trying a few more tests:

(1) The breaker trips even when both pier fixtures are disconnected (sometimes immediately and sometimes an hour later);

(2) I measures ohms with my very basic digital multimeter at the "20k" setting and found:
Hot + Ground = .10 and sometimes as high as 4.0;
Hot + Neutral = 2.8 to 4.0;
Neutral + Ground = 2.8 to 4.0.

* They are always changing and fluctuate every second.
* These readings are touching the red probe to the hot, if I reverse it and use the black probe on the hot, I get a negative low number like -0.3, a totally different number. I never learned resistance/ohms, so I don't know if that means anything.
* The wires are completely isolated
* I measured at the switch box then out at the pier and get slightly different numbers; I don't know if that's because they are changing so rapidly or if there is truly a difference.

So is this absolute proof that the wire is bad? If so, I'm screwed. This looks like a multi-thousand dollar job - running new wire underground 100+ feet in the woods with oak trees/roots every 10 feet and rocks/boulders everywhere.
 

Last edited by tony17112acst; 12-03-17 at 12:47 PM.
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Old 12-03-17, 01:04 PM
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If the wires are disconnected at both ends and you can measure resistance between any two conductors.... the cable is bad. Since you have resistance measured between all the conductors.... it would appear that there may be an underground splice.
 
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Old 12-05-17, 01:52 PM
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Although the results are truly a disappointment, I want to thank everyone who contributed to helping me figure out and to pinpoint the problem. Thanks again!

-Tony
 
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Old 12-05-17, 02:00 PM
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Maybe now is a good time to consider solar with a wireless switch? LEDs would draw so little power that even a small system could easily run them. Maybe even using 12VDC would be an option to eliminate inverters?
 
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Old 12-05-17, 02:40 PM
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Measuring very low resistances is difficult. The slightest amount of corrosion will skew the readings severely. Even altering the amount of pressure from the test leads to the wire will change the measured resistance. The only way it can be done is by firmly clamping the test leads to the wires being measured. I use alligator clips on the test probes or a short jumper with alligators on both ends between the test probe and the wire. Don't even have your fingers touching the bare wires or test probes.

The best way to test underground cables is with a special meter called a megohmmeter, often referred to as a Megger although that name is a registered trademark of the James G. Biddle company who made the first models many decades ago.
 
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Old 12-05-17, 05:29 PM
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Gunguy - I'm in the woods; no-can-do on the solar. Also I have a timer running from dusk to dawn for these lights which are already LED's by the way, so they run all night and solar can't do that ...yet. 12V DC is really something to think about. I already have 12V landscape lighting out there.

Furd - Hmm. You give me hope? I DID hold the test probes on with my fingers to give it a good connection. But a few times I did let my fingers off just to test how different the readings would be if I didn't touch them, and there was a lot more jumping around on the readings but it looked like it wanted to settle on the same readings I got with my fingers holding them on there tightly.

Today I decided to put the 4 switch gang box back together with all 8 wires in their place. I guess I'll have it dark out there, because I just cant spend a few thousand dollars on a light. There's no way to get a new wire under brick sidewalk and then under a masonry retaining wall and then through the boulders/trees after that.

I am very sad.
 
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Old 12-05-17, 05:40 PM
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Your stated measurements are much lower than the resistance of your skin.
Between those measurements and your problem description.... the wiring is leaking/shorting to ground.
 
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