one light fixture on multiple breakers


Old 11-18-13, 07:37 PM
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one light fixture on multiple breakers

Quick background followed by the questions.

Home built in 1950's in northern US. We've been in the house for ~10 years.

Three 12 gauge wires coming into ceiling light box.

Wire1=Black/White (no ground)
Wire2=Black/White (no ground)
Wire3=Black/White/Red (no ground)

Three black tied together (taped, not even using wire nut)
Three white tied together (taped), with a single white wire coming out of that bundle (pigtailed?).

The white bundle feeds the white cable on the light fixture, the single red wire feeds the black wire of the light fixture and there is only one switch (single-pole) that controls that single light fixture.

I shut off the breaker for the known light fixture. I then discovered the extra wires and used an AC voltage detector "pen" and discovered that there was still current on the black and white lines. The red had no current.

I then shut off the adjacent breaker and tested again, and the current was off.

My question is two fold.

1. Is that even "legal"? :NO NO NO:
2. If not, what is the best DIY way to correct the situation?

The fixture is on the main floor of a single story home, with attic access above (blown in insulation).

p.s. I did use my label maker and put a label at the fixture indicating that it required powering off two breakers (and which two) until the issue gets resolved.
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Old 11-18-13, 07:43 PM
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Welcome to the forums.

It's so hard to use one of those non contact detectors for actual troubleshooting. Based on the wiring as you described it there should not be two circuits directly supplying that area.

There could be a three wire circuit that ultimately feeds one of those two wire cables in your box and you may be reading that.

Do you have a voltmeter you could use to actually check for voltage ?
Old 11-18-13, 07:51 PM
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Thanks for the quick reply.

I do have a VM, but the fixture is back together (with the original light, the new one didn't fit the existing box).

With the second breaker on, the testing pen lit up bright red on the black and white lines.

With the second breaker off, the testing pen was dark around the entire wiring box.

Also, with the tape wound as tight as it was, I didn't want to start tearing the wires apart in the event they were live, and use my VM.
Old 11-18-13, 08:07 PM
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Based on the age of the wiring..... trying to get that tape off could damage the insulation. Once the insulation starts to fall off that opens a whole can of worms to repair.

It's possible that those wires are soldered..... then taped.
Old 11-18-13, 08:18 PM
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The voltage detector may have just been picking up the field from an adjacent circuit.
Old 11-18-13, 08:43 PM
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Join Date: Nov 2013
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Here is the wiring in a visual layout. What confuses me (because of my limited DIY knowledge of wiring) is what are those additional wires used for in the light fixture box. Other "typical" light fixtures in my home have a single wire running tot them with black/white lines and that's it.

As far as stray field, there is nothing in physical proximity to that light (1 in the image). There is a wall outlet 10 feet away (3), the light switch (on the same original breaker) (2) and a second ceiling light ~18 feet away. Not arguing, but just reporting my findings. The tester pen needs to be within ~3-4 inches of a known hot wire to light up. Since there is nothing in physical proximity to that ceiling light, and when turning the breaker off, the pen light does not light up, and when turning the breaker (second one) back on, it lights up, there appears to be voltage in those wires in that box.

I think the take away for me is that it may be best to call someone in locally.

Appreciate the feedback to this point, I'm sure I'll have more questions as I move forward.
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Old 11-18-13, 09:12 PM
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It's not uncommon to find that ceiling box is also being a junction to feed other circuits like the other ceiling light and receptacle(s) --- which is what those other cables are for.

With the vintage of your home and the fact there is a 14/3 coming from the switch to the ceiling boxe might indicate that the supply feed from the panel actually goes to the switch location --- the black & white are bringing the *hot* & *neutral* up to the ceiling box feeding the other 2 cables and supplying *neutral* for the light..
Old 11-18-13, 09:17 PM
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Turn off the known breaker for this light.

Flip the light switch back to on.

1. Does the light still come on?
2. Do you still read actual voltage (hot to neutral) on that circuit?

If the answers to both questions are no then you are reading phantom voltage and you do not have two breakers feeding the same light.
Old 11-19-13, 08:10 AM
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Three black tied together (taped, not even using wire nut)
That was a common method in the '50s on up into the '70s. Like PJ stated, they may be soldered, but may not be either. You cannot go into a '50s built house and expect to find wiring methods and materials of today. You need a meter to properly troubleshoot your wiring. The non-cotact testers are basically useless when troubleshooting.

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