I am new to this site and appreciate all your help. I tried to replace a light fixture in one bedroom with a newer, heavier one. The house was built in 1971 and has 2 circuits for all the lights. After turning off the power to the circuit that had the bedroom lights on it, I set about to replace one of the fixtures in a bedroom with a newer, heaver one. I installed a brace and new box and then went up to wire it.

The old fixture box had 3 cables of 12/2 coming into it. With power on, I used my voltage tester on each wire coming into the old box and discovered that all neutrals were hot as well as the blacks in the other cables. However, after I cut the soldered wires off and then checked again each wire with the voltage tester, I discovered that on one of the 3 cables coming in, the black wire was hot, the neutral was not hot (I'll refer to this as "sparky". This neutral had been "made hot" by the soldering of it with a hot wire.

So, I went about to connect the 3 cables again, making all three of them all hot like the electrician before me did. To do this it didn't seem to me to matter which wires were wired together since all were going to be hot anyway, right?

So I created two groups, each with one (originally hot) wires and an equal number of white wires and grounded all grounds together to the new metallic box, then made sure to pigtail between the 2 groups. I wasn't particular which wires from which cable went to the 2 groups, since on the old box, each wire was hot anyway. I then tied all grounds to the metalic box.

When I threw the power, the breaker tripped immediately. I am not sure what I failed to understand. But I obviously did something wrong. Any advice would be appreciated.

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Here’s 3 photos of the switch loop that I cut out.

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  • I took the liberty of adding formatting and changing your word "strands" to "cables". A cable is the thing about 1/2" across which contains 3 wires, black, white and bare. – Harper - Reinstate Monica Nov 6 '17 at 18:24
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    Why do so many try changing a working circuit? I shouldn't complain as this has made me lots of easy service calls in the past. – Ed Beal Nov 6 '17 at 19:52
  • Hi! You have a couple of user accounts. Please merge them together, which will allow you to edit, and comment on any of your posts and accept an answer on your question. Thanks, and welcome to the site! – Niall C. Nov 8 '17 at 15:21

Mistakes were made. It happens.

  • taking apart apart all the wires instead of just the 2 conductors the lamp was actually attached to (other than ground). This happens a Lot.

  • not taking photos before the fact.

  • "White" is a color. "Neutral" is a function. Confusing them. The trouble is, cables are manufactured only with certain colors (white and black), and you are stuck with those colors even though the wires will in fact have a variety of functions.

Ideally, you re-mark the wires with colored tape - black for hot, red for switched-hot, yellow for messengers, blue/purple/green/etc. for alternate hots, or whatever scheme you prefer. However the vast majority of "in a hurry" high-production installers never do that.

Now in residential cables, there are special rules: white/gray can be reused/remarked as hot wires, but colored wires cannot be reused as neutrals. Nothing can be remarked as a ground, and green/bare can't be remarked, so green tape on a black wire makes it still a hot.

In a switch loop, it's common practice (and now Code) to make the white the always-hot, to help the next guy identify it as not a neutral (since a voltage tester will reveal hot all the time, even if the switch is off.) The other wire in a switch loop is switched-hot, neutral is not present, (but is now required in new construction to support smart switches).

"switch loop" is the word I want you to Google, because this is where things went wrong in this setup. One of the wires coming back from the switch is actually "switched hot", as is the hot wire to the lamp obviously. Mark those red. Once you have done so, then you can match by color.

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  • Thank you Harper! I will learn all about switch loops and then take them apart and re-mark them with color and see what happens. – Kevin Mack Nov 6 '17 at 22:07

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