Bulbs Burning Out

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jtr

Member
2 Separate Circuits in a new kitchen keep blowing out bulbs every couple of days. These circuits have been fed with 12-3 wire. Sharing the neutral. Not sure who wired the kitchen but the homeowner can not get a hold of the contracter who did the work.

There is no access to any of the wire. There is a junction box they said behind a counter that now has tile behind and a marble top. They don't want to remove it if they don't have to.

Any clues as to what to look for that may be of help would be greatly appreciated.

They do have a new ceiling fan next to one of the lights but the vibrations are minimal and I checked the lights for overheating.

Thanks
 
K

kiloamp7

Senior Member
Re: Bulbs Burning Out

Yes, When a "multiwire" circuit is involved, (a circuit with a neutral that is "shared" between opposite hotlegs) check for loose or open neutral.

This is usually one of the first things to check on this type of circuit. In your case it is just a branch circuit(s), but the same characteristics of a multiwire circuit also apply to feeders & services.
 
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jimwalker

Senior Member
Location
TAMPA FLORIDA
Re: Bulbs Burning Out

First i dont suggest you touch the system as that could void warranty.A call to the building dept.should get you results and at least the company name that wired the house.Any chance that someone messed something up at that fan box.Not uncommon to see electricians use a nutral as a hot and forget to remark them with phase tape.If you had a part in the fan install recheck your work.
Did this problem happen just after fan was installed ?
 
B

bobh

Member
Re: Bulbs Burning Out

That junction box definitely needs to be uncovered cause of a code violation & might be the root of the problem. I can understand not wanting to rip up the tile, maybe you can access the box on other side of wall & turn it around? Just a suggestion.
 
W

wireddd

Member
Re: Bulbs Burning Out

There must be access to the wires where the fixtures are. If you check all these and they are tight and you can't get to the junction box,
find the feed at the switch or lights, cut it off and run a new feed to this point.Also check the quality of the bulbs, fixtures and sockets.
Who runs #12 to lighting circuits in a residential kitchen anyway?
You also may be able to get to the junction box through the inside of the cabinet. Cut a portion of the back and drywall out.
 
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jeff43222

Senior Member
Location
Minneapolis, Minnesota
Re: Bulbs Burning Out

I agree with the others that a loose or open neutral is the likely cause. You can check for this without doing any demolition work by testing the voltage at the fixtures in question. If the neutral is loose or open, you're going to see voltages that differ significantly from the nominal 120V you are supposed to have. A loose neutral on the circuit you described will transform your 120V multiwire circuit into one 240V series circuit. That would easily account for the bulbs blowing up.
 
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highkvoltage

Senior Member
Re: Bulbs Burning Out

First,if you have a circuit tracer that can locate wires behind a wall, start there. I find it hard to believe any inspector would have passed that installation so I feel that you may have been misinformed. You can then map out the entire wiring system in a short period of time and then lay out a plan to find the problem without guessing and doing any unnecessary damage to the building. I have used this method many times and it saves time and money. I also agree that you may have a bad neutral connection or the white wire was used as a switched leg didn't get marked correctly and you have 240 at the lights either though another light, the fan or something other than the ovious down line. If you have the circuit mapped out you could attach your volt meter to one of the problem lights and start turning other appliances or devices on that circuit and possibly find the problem. Good luck.
 
physis

physis

Senior Member
Re: Bulbs Burning Out

I agree with Jim. If there's a warranty issue don't mess that up. If it's dropping the neutral It's gonna be hard to catch if it's intermitant. If it's constant you'll only need to unscrew a bulb! You can also check to see if two breakers turn off the same set of lights.

And light bulbs now days are the closest thing to garbage you can find being sold new. It could easily be that simple anymore.
 
engy

engy

Senior Member
Location
Minnesota
Re: Bulbs Burning Out

Just had a buddy check out lights at his mom's place. The lamps were literally exploding. I gave him pointers from open neutral, to cheap lamps. As it turned out his mom was buying them from the dollar store or something, anyway, he bought some "good" bulbs and problem solved.
 
physis

physis

Senior Member
Re: Bulbs Burning Out

But unless there's a voltage divider set up it's unlikely you would find 208 on single phase. :)
 
M

midget

Senior Member
Re: Bulbs Burning Out

Heh...some idiot told me that was just 2 hots without a netural, and that is was single phase...but still...I'm not understanding how when you lose a netural, that it comes up as some different votlage, which makes light burn out, instead of them just not working at all. I mean...you can't have 220v w/o a neutral, can you?And what's a votlage divider? :p

[ December 06, 2004, 02:00 AM: Message edited by: midget ]
 
physis

physis

Senior Member
Re: Bulbs Burning Out

Midget,

Ed MacLaren has a good schematic illustraion he posts sometimes for this question. If you ask him he may post it for you. :)
 
E

Ed MacLaren

Senior Member
Re: Bulbs Burning Out

Perhaps this sketch will help.

To relate this to a typical residential installation, each of the resistor symbols represents the loads fed from a bus of the panel. Notice they are quite unbalanced.

The open neutral causes the two loads to be connected in series across the 240 volts.

The two loads "divide the voltage" in proportion to their resistance. If the loads are not balanced, the higher resistance load can see a damaging overvoltage.

Ed

3wire3.gif
 
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