Breaker trip randomly and wont turn back on

[BREEZY]

Hey guys,
Figured id give this a shot after I've spent a couple hours at a customers house trying to figure out an issue.

Customer called yesterday that their under cabinet lights randomly went out while they were on the couch watching tv. They noticed that the switch wasn't working so they went down to the panel and saw breaker tripped. Tried to turn it on and it just kept on tripping.

I arrived there today to spend a couple hours on it after working another job.

This breaker controls:
kitchen under cab lights
microwave
hallway bath lights
hallway bath gfi
hallway lights
hallway stair lights/ fan
attic lights
small gable vent fan
master bedroom fan/light
master bedroom bath lights
2 outside lights

Circuit is on a 15 amp breaker, now clearly someone added a ton of stuff to this circuit which would never fly and I wouldn't recommend.

First thing i did was switch the hot to another breaker to rule out bad breaker but it popped instantly. I tested my HOT wire to the neutral bar and got continuity and a resistance of 9 ohms.

started taking apart switches to test if there was continuity between hot and ground and there was. I told the customer after a couple hours after troubleshooting that I would have to return to do some more troubleshooting seeing as I'm going to have to figure out where the issue lies. The hardest part is having all these things on the same circuit there is a lot of spots there could be a fault.

I unplugged the microwave and anything that was plugged into an outlet. Still continuity between hot and ground/neutral

Just trying to see if anyone else has ever ran into this issue before of a randomly tripped breaker that wont turn back on and then had continuity between hot and ground.

Thank you!

 

[LarryFine]

When troubleshooting a circuit with a direct short circuit to either neutral or ground, it's difficult to find the fault because you can't keep the power on long enough to look, so the only other way to find the offending undesired connection is visually, box by box.

I typically use a rubber socket with a 150-watt bulb screwed into it, and wire it in series with the problem circuit at the panel. I disconnect the circuit's hot wire from the breaker terminal, connect the socket's black wire to the breaker, and wire-nut the circuit's hot wire to the socket's white wire.

With the high-wattage bulb in series with the circuit, the breaker will stay on because the most current that can flow is that of the bulb, so it acts as a current limiter. It also functions as an indicator, steady bright for a direct short, flickering for an arcing fault, etc., with you or a helper watching it.

 

[don_resqcapt19]

You are always have continuity between the hot and neutral if there are any connected loads.

 

[LarryFine]

You are always have continuity between the hot and neutral if there are any connected loads.

That's why I use a high-wattage bulb.

 

[SeanOliver]

Find out if they have recently hung any pictures, repaired siding or nailed anything to a wall.

 

[TwoBlocked]

I'd take a stab with the outside lights. Get a good visual inspection. They get the worse abuse.

If you take the neutral off the bar, and the hot still has continuity to the bar (or ground), then it is grounded. otherwise it is shorted to the neutral.

LarryFine's idea would put an amp or so through the wiring before the short/ground. If you can put a clamp-on meter on the hot wire (where you can get to it) it should tell you if you are beyond the short/ground or not.

 

[ptonsparky]

I've run across more than one fixture with the center tab twisted out of position until it makes contact with the screw shell. Often held in place by a newly installed lamp.

 

[readydave8]

By the way I don't like that method of testing for bad breaker

I either pop breaker out to see if it trips without being energized, or take wire off breaker

 

[sunny1]

I'd try to guess roughly the geographic 'midpoint' of the circuit and open up one of the outlets (or a switch) where power passes through. Seperate the hot connection and if the breaker still trips, then the problem is closer to the panel. if not, then the problem is farther down stream. That can help narrow it down.

 

[BREEZY]

Thank you all for your replies,
Yeah it is very strange but happens often I'm sure over the years. According to the customer they haven't done or changed anything. They were simply sitting on the couch when the lights went out and the breaker tripped and wouldn't go back on.

They did mention last week power going out due to a fallen branch outside their house, it was out for about an hour or so then came back on. So everything was working fine for a week then this happened.
He also said they do have mice in the garage and I did see some dropping's in the panel.....Not even sure how there could be there really is no access to the inside of the panel. My first thought was maybe a mouse is in the walls and chewed through the wire.

Looks like I'll give the bulb test a shot and see if that can help. If not it looks like I'll just have to go box to box and separate the wiring to narrow it down.
I was just curious if anyone has ran into this in the past and found the culprit to the issue.
I did take a look at one of the outside lights because it was easily accessible, Ill have to take a look at the other one and see if there is anything going on. The only thing with that is they are on switches so as long as the switch is off I shouldn't be reading through them.

I've had issues in the past where a GFCI kept tripping in a kitchen and I thought I had continuity between the hot and the ground but come to find out there was a transformer tied into the circuit on a box and was causing the GFCI to trip.

 

[TwoBlocked]

Yeah, I had something similar with a GFCI breaker. A bit intermittent. The fault was between the neutral and ground where MC came into a handy box in a garage. Using a megger helped because it was not enough to show with an ohm meter's 3 volts. Sunny1's "divide and conquer" idea is good, IF you can figure out how the circuit runs. Otherwise you might have to go box to box and count the wires going here and yon to make sure you don't over look the outlet behind the china cabinet. A wire tracer can help.

 

[BREEZY]

Thank you twoblocked,
Another theory I had was that there is so much on this circuit, not that all of them draw that much current because they're lights but because the microwave is also on this circuit that it may be pushing the limits a bit much for that circuit and possibly melted something along the way maybe in one of the ceiling fixtures or bath lights.

 

[TwoBlocked]

Thank you twoblocked,
Another theory I had was that there is so much on this circuit, not that all of them draw that much current because they're lights but because the microwave is also on this circuit that it may be pushing the limits a bit much for that circuit and possibly melted something along the way maybe in one of the ceiling fixtures or bath lights.

With too much current, the breaker SHOULD trip before any wiring is damaged. Doesn't really matter what caused the fault. You just gotta find it.

 

[PaulMmn]

Mice, squirrels, other rodentia love to nibble things to keep their teeth trimmed. Any bees occupying a box and shorting things out with honey?

 

[tthh]

If a tree fell on an aerial drop, perhaps one of the wires came loose in one of the h-taps?? Not sure why it would only affect that breaker, but that's a notable recent event.

 

[Sea Nile]

I would try to find a very sensitive precision ohmmeter. The kind you would use on electronics.

Measure the resistance at each device location and the point with the lowest resistance will be closest to the problem.

 

[gar]

230811-1009 EDT

BREZEEY:

Do as Larry Fine suggested. I would suggest a 250 W tungsten bulb. Then disconnect all loads on your circuit from their outlets.

Now use a meter that can read various low voltages from fractions of a volt to 250 V. Create a long test lead, #20 wire is a good choice, from the light bulb output terminal where you connect to your hot conductor. This becomes your common reference point for voltage drop measurements. Extremely low current will flow on this long test lead, and therefore this provides a reference point from the output side of the bulb. Note: bulb resistance of a tungsten filament lamp varies greatly with current, but this does not matter in this experiment.

If you measure voltage to your AC common wire you will see some moderate value. This is a function of the current flowing thru the 250 W bulb. If there is no shunt load after the 250 W bulb it will not glow, and voltage will be near full line voltage. If there is some unknow loading after the bulb, then the bulb will light to some extent, and the voltage from the 250 W bulb will vary depending upon where you connect the second meter lead. *10 copper wire has a resistance of about 1 ohm per 1000 ft. Thus #13 has about a 2 ohm resistance at 1000 ft.

Next you go to various outlets and measure the voltage drop from your reference point, the output side of the 250 W bulb, to the hot terminal of the outlet. Nothing has to be opened to do these measurements. The results should guide you to the general region to look for the specific problem.

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