Why is breaker tripping?


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Old 05-03-08, 07:27 PM
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Why is breaker tripping?

I am in the process of changing a light fixture. The power is in the switch box and a single 14-2 wire travels from the light switch the light fixture. There are no other wires. I turned the light switch off and tested the wires and got no voltage. You can even touch the black and white together and nothing so I know for sure there is no power to the fixture. The junction box in the cieling is metallic and the ground wire is screwed to the junction box. There is no light fixture in place, just the ends of the black and white wires. If either the black or white wire touches the junction box it trips the breaker. No sparks, nothing-- just trips the circuit. This is a new house (2005) in it's in the MBR so it has the Arc fault breakers on this circuit.

Is this correct? If so, how can it trip the breaker if there is no power up there?


Thanks
 
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Old 05-03-08, 09:23 PM
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How did you determine power was in the switch box? Do you have two cables in to the switch box. In other words two black and two white wires (plus grounds)? If power does come into the SWbox then the two blacks should go to the switch and the whites should be connected together (but not to anything else).
 
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Old 05-03-08, 09:42 PM
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With AFCI's they are pretty picky just like GFCI are and if you get a small nick on wire insluating materal that can touch between netrual and ground it will trip it.

ditto with new luminaire if you are installing you may want to double check make sure there is no pintch point or anything can trip the breaker.

did you try to reset the breaker ??

[ just wondering what brand breaker you have there i know one brand did have small issue but took care of it by now]

Merci, Marc
 
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Old 05-04-08, 05:59 AM
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If the breaker is AFCI it also has GFCI . Grounding the neutral will cause some current to flow though ground instead of neutral (parallel path) and trip GFCI.
 
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Old 05-04-08, 08:44 AM
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Originally Posted by joed
If the breaker is AFCI it also has GFCI . Grounding the neutral will cause some current to flow though ground instead of neutral (parallel path) and trip GFCI.
AFCI's and GFCI's are two different types of devices and are not the same. That is why they are starting to make combo AFCI/GFCI breakers. AFCI protected branch circuits in kitchens and bathrooms still need GFCI protection at the devices.
 
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Old 05-04-08, 09:29 AM
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The breaker is AFCI only. It is a Murray that has small window on it that shows is showing yellow (the others in the panel are clear) so I assume this some type of diagnostics.
 
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Old 05-04-08, 11:12 AM
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I have pretty much worked on most AFCI's other than Murry. I believe the yellow is showing you have an arc fault (as opposed to an over current which would trip the breaker handle to the middle position) If you touch the neutral to ground the AFCI will trip. Even if there is no power to the switch leg of the light there can be a small amount of voltage on the neutral. AFCI's are VERY sensitive and may detect this and trip.
 
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Old 05-04-08, 12:43 PM
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Thanks Tolyn,

The small amount of voltage you are refering to, is that the same as "phamtom voltage?" Is the volatge "jumping" from another source or capcitated between the wires?

also, the same thing happens when either the hot or neutral touch the ground, does that make a difference?


Bottom line, I don't have to worry about the house burning down????
 
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Old 05-04-08, 04:29 PM
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AFCI breaker are different than GFCI. However they also have a sensor that will trip on similar faults to GFCI. If the neutral and hot current are different they will trip. The trip level of a GFCI is 5 ma. It is higher in a AFCI and therefore does not qualify for GFCI protection.
 
 

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