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Background

I had a wall outlet wired like the one below. I wanted to move it over about 4 feet, so I bought some electrical wire and used it to extend the existing wire.

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As you can see, it was two wires that needed to be extended.

Here's how I spliced the wires:

Basically, I twisted the bare wires together, then pigtailed them, wrapped each pair in electrical tape, then electrical taped the bigger white/yellow line pairs together.

I bought a new, standard duplex outlet and wired it up so that one extension wire was wired to the top outlets and one was wired to the bottom. I pig-tailed their grounds together with a third bare wire and connected the bare wire like this:

Problem

Everything was working fine for a few hours and suddenly a breaker on a different circuit tripped, shutting off the lights in the adjacent hallway. The new outlet that I had just installed still worked just fine.

Originally, I didn't break the metal break-off tab on the new outlet. While troubleshooting this, I broke it, still experienced the problem, and now the bottom plug doesn't work while the top one does.

I also tried swapping breakers to eliminate a bad breaker as the cause, but that didn't help, either.

Questions

1. Is it possible that my wiring job caused this other breaker to trip. If so, how?


2. If it is due to my wiring job, what can I do to fix it?

Edit - Panel Pics

I can't figure out the problem yet. Here's what I do know. And I have to save it because I can't visit chat without losing this.

The old junction box MUST remain

It is not legal to remove that junction box. You are required to make all splices inside junction boxes, and cannot bury them inside walls (splices or junction boxes). Every junction box cover must be reachable without use of tools of any kind. You can make your extension splices inside the box, whether it has a blank cover or a receptacle.

It can have a blank cover, unless...

You need a receptacle within 6' of any point on a wall

You need to follow this wall its entire length between thresholds, (including around corners) and make sure there is still an outlet within 6' of every point along the wall. So, within 6' of a threshold and every 12' thereafter. This rule is because standard lamps and appliances have 6' cords, and you need to be able to route the cord hugging the wall (no cutting corners).

If you didn't have that situation before, the old situation may be grandfathered (legal now since it was legal when installed or modified). The rule with grandfathering is you can't make things worse. So if any area of the wall lost coverage because of the move, then you need to retain the receptacle at the old position. (You can still have the new one).

Mechanical execution of work

The lower picture looks perfectly proper. Wires must be 6" long past the cable clamp, and stick out 3" beyond the wall surface; don't get any shorter than that.

2 circuits or not?

If the first photo is of your actual box, it indicates that all wires are feeding the same socket of the receptacle. That means we can exclude "2 circuits" or "split switched outlet". For sure, the two blacks in the old photo are spliced to each other via the outlet. Ditto the two whites.

This means only one circuit is in play (assuming there are not wiring defects elsewhere) and you only needed one cable, not two, to extend this circuit. The other cable is superfluous. At the old box, all blacks can be joined at the old box with a wire nut, and all whites ditto. That will also reduce wire fill count to a sensible number.

If you need a receptacle at the old box, either avoid using the receptacle as a splice and use a pigtail to attach to the receptacle. Or use a "screw-to-clamp" type receptacle which gives four wire points per side. Do not use backstabs (as in first picture), because backstabs cause nuisance problems, with opens or arc faults; but also, backstabs can't work with 12 AWG wire, which is your yellow cable there.

The box must be large enough

For instance it appears your old box will have

• four 14 AWG wires (judging by the backstabs) which take 2.00 cubic inches each


• four 12 AWG wires, 2.25 c.i. Each


• Pigtails are free


• a bunch of grounds (which count as 1 of the largest wire) so 2.25 c.i.


• cable clamps (which count as 1 of the largest wire) so 2.25 c.i.


• if you have a receptacle, 2 of the largest wire connected to it. (4.50 c.i. If yellow jacket #12 wire is involved, otherwise 4.00 if using #14 pigtails.

If you need more cubic inches, before grabbing the claw bar, google "surface conduit starter box". It's for launching surface conduit out of a flushmount box, but if you only use it for cubic inches, I won't tell :)

Harper is absolutely correct that all junctions must be in a readily accessible box. This is both for safety and maintenance reasons - a junction hidden in a wall is both a fire hazard and potentially a headache for any potential future rewiring. The 6ft distance between receptacles is also required by code, but would only cause a fire hazard if it lead to a mess of extension cords being used (which is probably the cause for its addition to begin with, based on a lifetime of living in older houses that only had one receptacle per room).

I also recommend you twist your wire nuts more - the wires should visibly wrap around each other at least twice to ensure a reliably tight connection. Loose wires are a big headache, not to mention potential fire and shock hazards.

That metal tab on the side of your duplex receptacle is intended to connect the top and bottom receptacles in parallel. It only needs to be removed in the case that each receptacle has its own circuit, which is uncommon in residential wiring. That's why your bottom receptacle stopped working. You'll probably want to buy a new receptacle to avoid a mess of splicing.

However, to answer your question, I doubt that your wiring on one circuit caused another circuit to trip. I can't come up with a reason why that would occur. If swapping breakers didn't prevent the problem, it's probable that there's some sort of electrical fault happening on that circuit, or perhaps too much power is being drawn on it (is it only lights, or are there also receptacles on that circuit? If it's only lights, it's pretty unlikely that they're drawing too much power - but don't trust what the breaker box labels say, actually check to see if there are any receptacles not working while that breaker is tripped).