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Question DetailsAsked on 7/17/2015

Wire came loose while changing light switch and now power doesn't work on that circuit

I was switching a light switch and when I put the replaced switch back into the wall a wire must have come loose. I didn't know that and turned the power back on. Now the power doesn't work on that circuit. The switch had 2 black wires on it. I opened the area back up and reconnected the wire that came loose but still no power. Nothing looks out of the ordinary in the light switch socket. Any ideas?

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4 Answers

Voted Best Answer
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I am not sure from your description if you have the wiring all right or not - reasd the below descriptions if not. If yes, then when the black wire came off it may have contacted the ground or metal and tripped the breaker, so once your wiring is all correct you will likely have to reset the breaker - as well as any GFCI outlets that might be in that circuit.

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Not seeing your exact situation, but assuming this is an ordinary light switch - not a fan or multi-function switch - GENERALLY, you would have cable with a black (live), white (return or neutral), and a green or bare copper (ground) wire coming in to the box. These might come only to that box (if last in circuit) or might be wire nutted to matching colors that continue out of the box to the next switch in the circuit. This in addition to the three wires coming from the light itself.


BTW - when I say "cable" I mean the probably plastic-encapsulated Romex or flex metal (BX or similar) conduit or similar bundle of three wires that make up the "circuit" - by "wire" I mean a single wire of a particular insulation color from within a single Romex or similar cable run.


For a simple light switch, the incoming or "live" black wire (or if not at end of circuit, a pigtail black wire from the black wire splicing wire nut) would come to the connection on the switch, then another black wire would run from the switch in a cable out to the light. With a simple one-pole (just on-off) light switch, the white wires in the box would all be wire nutted together and none of them would connect to the switch - just the incoming cable white wire into the box connected in a wire nut to the white wire from the light, and may also be wire nutted with an outbound white wire in the cable to the next box in the circuit. The green/bare ground might also be wire nutted to an outgoing lead to another box, and would be wire nutted to the ground wire from the light. Should also have a ground pigtail to the green screw on the switch, or sometimes only to a clamp in the box if the box is metal. Here is a typical wiring diagram -


http://www.buildmyowncabin.com/electr...


Note the ground wire (green or bare copper) is shown in yellow on that diagram, and he did not show each of the wires possibly continuing on to another box in the circuit - so this illustrates a dead-end (end of circuit) wiring - but is same if mid-circuit except each wire nut will also have another wire leading to a cable going out of the box to the next one.


Here is another diagram - showing brown for ground this time - which is a bit clearer, but again is for a dead-end switch box, without any leads going on to other switches -


http://www.noguge.com/ceiling-light-i...


If you only have two cables coming into your box, you are dead-ended like these. It you have three pieces of BX conduit or Romex or such coming in, then you are in mid-circuit and will have incoming, outgoing, and light fixture feed cables in the box. Most light switches will be "dead-end" - with the continuing circuit connection occurring in a connection or junction box, but not always.


It is quite possible your two black lead wires at the switch are not making proper contact - stripped too short if you used the push-in connection holes on back, or not stripped adequately or not tightened in under the screw if you did it the better way - or you curved the wires the wrong way at the screw (should curve clockwise) so when you tightened the screw on the switch one or both wires popped out.


It is also possible your black and/or white wire nuts are loose or one wire is not all the way in - you need to trim the insulation back so all have the same exposure (without being exposed past the wire nut), twist the wires together clockwise, then put on the wire nut and tighten down - then test pull on each wire to be sure the wire nut gripped it properly. If not, one is short in the bundle, or wire nut is too large or too small for number of wires in it. You should be good on that, since you have the same number of wires as originally in use.


All else fails, Electrical is your professional Search the List category.

Answered 4 years ago by LCD

0
Votes

MORE INFORMATION:


Here are some photos of the 2 switches I installed. The 2nd one is a ceiling fan with a dimmer for the fan lights next to it. The dimmer has a red wire and a black wire that goes to a wire nut which also connects to the fan switch. There is also cream colorded wire that is wirenutted. I can't see any problems. The breaker will stay on but no electricity is available anywhere on the circuit so I turn it back off. My breaker doesn't have a way of resetting unless the breaker is thrown (that I can see). All of the other circuits work without a problem.

Answered 4 years ago by mikeiskool

1
Vote

Since you said no power on circuit even with breaker back on, look for a GFCI outlet on that circuit (would be on the breaker side of those boxes) that might have tripped out.


Can't see enough on the one by the slider switch to tell anything there.


On the stand-alone switch, you are in mid-circuit (power passes through the box and goes on to other same-circuit boxes, hence three wires of each color), so a wiring problem in this box would stop power to all other boxes down the line in that circuit.


Even after enhancing the photo I could not trace all the exact wiring, with the bends and darkness in the box and all - but all I see is two white wires to the wire nut - did one not get connected ? If the incoming white lead from the breaker box is not connected, would kill everything from that box (including the light) on through to the end of the circuit. If the white wire leading to the next box is disconnected, you would have power and light should work, but rest of circuit would be dead. If the light run one is disconnected, only the light would not work - these all assuming the white wire is not touching metal so it is maintaining the current through the metal to ground.


I would assume the right-most pigtail (from switch to yellow wire nut on black wire connection) is the power tap for the switch/light, and the leftmost wire is the outgoing wire to the light. IF that is the case, that bend in the pigtail wire is WAY too right - even if the wire is not broken in the bend, that tight a crimp reduces the diameter of the wire so is a fire hazard, both due to the reduced wire size and the fact the crimped bend cannot dissipate heat proiperly - that pigtail should be replaced regardless (not just straightened, which could crack the wire), though if wiring is as above that would only affect the switch/light. If wired backward like next paragraph, nothing except the incoming lead and the switch would be live.


IF, instead, the leftmost wire, coming direct from cable to the left lug on the switch, is the live line from the breaker, that is wrong - because power would run to the switch, but onward from there in the circuit ONLY when the switch was on - not the way to wire it. The switch should be powered from a pigtail to the splice in the wire nut, then from the switch to the cable leading to the light fixture.


If you are electric savvy and know how to use a volt-ohm meter, you could do the following - otherwise call an electrician. If you disconnect the wires from the switch and leave them hanging free of metal (beware of kid or pet access) then turn on the breaker, check which are live - if left one, that is the incoming lead to the box and should be wired to the wire nut for the black wires. If the right one is live and the left is dead, then probably black is wired right, so your problem is likely in the wire nut (assuming this is the box with the issue, not the other one). You might have to disconnect both the switches and the black wires at the wire nuts initially and use the volt-ohm meter to see which box is first in line (the one with a live wire coming in to the box) then work from there on first connecting the box-to-box wiring back up right so you know you have power (black) to both boxes, then check black to white and black to ground for 120V continuity (and recheck white splices if not getting 110-120V from black to white), then after you are sure you have power to both boxes and ground is grounded to each box, then turn power back off and go back and install one switch at a time, and test both the light / switch working, and power getting to the second (downstream) box before going on to the next box.


One other possibility is that the breaker failed when it tripped - happens especially with very old breakers. If you know of an outlet or light that is closer to the breaker in the same circuit, it that outlet/light is also not working, then the breaker is likely the problem - or a connection somewhere in the circuit failed when the stray wire shorted out. I have seen wire nuts blow apart and the wires separate in connections in a real good short, and breakers can fail, so it could be your power is interrupted at the breker or somewhere else in-line - to determine that you would have to be electrical savvy and check continuity at each box along the circuit until you find the failure point.


If not pretty wiring savvy, make the outlets safe from people walking by/pets/kids and call an Electrician - Electrical is the Search the List category.

Answered 4 years ago by LCD

0
Votes

I went through both outlets and couldn't find a live wire in either box. Both boxes had 3 black and 3 white wires in wirenuts making a good connection. Could it be the breaker itself?

Answered 4 years ago by mikeiskool

1
Vote

If all black wires in the two boxes are dead, then the problem is "before" that - could be a burned out wire in a preceding box or a place a wire in the runs between boxes burned through due to high amperage (which should not happen unless breaker failed to trip), a tripped GFCI outlet between the two boxes and the breaker, or a bad breaker.


Occasionally a breaker will not trip all the way - if OFF now, turn to ON, then OFF, then back to ON and then check if there is any power on that circuit, but like before if no power to the circuit turn back off and leave off. Whatever you do, use a quick flip (or push for pushbutton type) - do not hold the lever or button in position in case it needs to trip right back off again.


Other than those thoughts, time for an electrician - because any further investigation in the breaker box like a continuity check or trying the wires on a new breaker are not for the amateur even if electrical handy - both from a safety standpoint, and also because you are playing with one or two hundred amp capacity in the breaker box, so a mistake can cause a significant fire and a lot of $ damage in short order.

Answered 4 years ago by LCD




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