strangely behaving lighting circuit

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  #1  
Old 08-25-15, 03:22 PM
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strangely behaving lighting circuit

I had a circuit with switch servicing three ceiling fixtures in my basement. I cut the wire between the switch and the first fixture, put in a junction box and pigtailed a short piece of wire to add a forth fixture. Now, when i flip the switch one way the light i added comes on and when i flip it the other way, the origonal three lights come on and the light i added goes off?? they cannot all four be turned on together, but are wired to the same switch. I rechecked all wires black on black white on white. How is this possible?
 
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  #2  
Old 08-25-15, 03:46 PM
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The line you cut was a "switch loop" and not the power going up to the lights. The white was not a neutral.

Connect everything back the way it was, remove the line going to the fourth light fixture, (but leave the respliced original wire ends inside the junction box).

Run a cable from one of the existing light fixtures to the fourth light fixture, matching whites and blacks.

The way you had it, when the switch was "off," current arrived at the first existing light and split three ways to flow through those 3 lights. Then the current converged, went down towards the switch, and flowed through the fourth light. (And then back up and behind the first light to return to the panel.) Only enough current flowed to light up the fourth light and by being split up going through the first three lights, each of those three did not get enough to light up with.

When the switch was "on" enough current flowed to light up the first 3 lights despite being split three ways. Next, the current converged, went down towards the switch, and split again, this time two ways, through the switch and through the fourth light. But the switch in the on position was a much easier (less resistance) path so most of the current went that way. Some current went the other way, through light 4 but not enough to light it up.
 

Last edited by AllanJ; 08-25-15 at 04:21 PM.
  #3  
Old 08-25-15, 05:01 PM
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wow thanks so much allen, I have done a fair amount of electrical work (novice) and would have never figured that one out.
 
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