Can Lights Blow Fuse

At a property we have 2 can lights in a bathroom. When the switch is flipped it blows the breaker. Conditions....

--It's not run through a GFCI. That's on a separate circuit.

--It makes a buzz sound when the switch is flipped....then breaker blows in about 2 seconds.

--If I take the bulbs out (50 watt short neck flood incandescent) then flip the switch, the circuit still blows, but I don't hear the buzz sound.

--Nothing else is on that switch.

--There are other switches for lights, and an exhaust fan on that circuit blowing circuit, but they are all fine.

--Switch has been checked and it's good. (SP switch).

--House is circa 2004. No upgrades anywhere noted.

--Took the can trim out--saw nothing odd or wet up there.

Many thanks in advance for the help!

 

Sounds like you have a high resistance short somewhere . Did this just recently start?

 

Yes started last 4-5 weeks...could it be bad breaker? It's on an SP twin SQ D type....

 

If it is a bad breaker it would not reset. The issue should be after the switch since the breaker is fine with the switch off. First pull the switch out to make sure there are nothing touching in the box that shouldn't be. If that is fine then move to the cans.

Since they are can light you need to remove the can and access the junction box above the ceiling. The last can will only have one cable going to it. the middle can will have two cables to it, one in from the switch, one out to the last can.

Open the box and disconnect all the black wires, cap them off, and try the switch again after resetting the breaker.

 

Thanks...will do tomorrow, starting at the first can.

 

OK so here's what we did & the results.

--Disconnect 3 wires in 1st can J box, 1 from switch, 1 to can socket, 1 to other can. Flipped switch and still tripped breaker.

--Disconnected & separated ALL wires in 2G box, incl 2nd switch. The extracted 2G box from wall. Carefully looked at all wires, esp around stripped cable sheathing. Looked into wall too. No evidence of anything damaged or snorting.

--Then took incoming hot & neutral feeding 2G BOX and direct connected to outgoing Hot/Neutral outgoing to can. (no switches yet) Turned on breaker --light works, no blown fuse.

Sounds good so far, even though I didn't identify how the original problem got 'solved'. But...

-- Installed new 2G box, then everything & switches re-terminated properly. Flipped Switch & FUSE Blows AGAIN.

--For the heck of it I took the gnd off the switch. Still blows. (plastic box anyway) I tried a different switch also--still blows.

My thinking is that there's an intermittent short between the switch and 1st can. And my next thinking is install a new cable between these points. (chopping back the old cable so it can't be re-terminated.) Which would mean a few ceiling holes.

Any other thoughts? Is this a good course of action?

Lastly, aren't some kind of signal testers that will diagnose shorted points? Where do I get one?

Thanks very much!

 

I would look closely at the cable one more time before replacing the cable. It can get damaged in the wall, but it is rare excluding animal damage . It sounds like the damage is close to the switch box.

Does the cable go switch light light or switch to light one and switch to light two?

 

Based on your first test, I also suspect that something is wrong with the cable from the switch to the first can light. I would recommend installing a new cable and abandoning the old one. Be sure that the above test is true by double checking everything before committing installing a new cable.

You can test a cable by just using a volt/ohm meter set to ohms or continuity. The closer to zero you get, the worse (less resistance) the short. There are testers that will find shorted wires/cables but they are stupid expensive.

 

Same switch to both lights and I looked very closely at the 2G box cables esp near stripped sheaths and beyond as far as possible.

 

OK so cable replaced from switch to can, and all is good. Here's a pic.

Animal destroyed wire and bath fan duct. It came in the outside vent hood, then trashed the 4" flex duct, (insulated plastic duct) got in through the duct hole you see and trashed the wire.

Does any know what type of animal did this? The exterior vent hood had a critter guard with about 3/4" square holes.

 

I live in the woods and have critters all over the place, mice seem to be the ones that love to chew everything in sight. The squirrels just leave acorns all over the place and leave everything else alone, no issues with opossums or skunks chewing anything either, it is always the damn mice and they can squeeze through a hole the size of a dime. The best way to identify a critter is from droppings, mice leave them everywhere.

I just get those covered spring traps and bait them with peanut butter, I have a cat, but she is a step slow and just plays with them.