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Old 09-16-2013, 09:21 AM   #1
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Light Switch wiring


Just moved into a new home....former owner was doing some odd things with wiring that I am now trying to correct. He left this light switch wiring exposed as though he just gave up on it or whatever. There are three wire cables coming into the box. The three white wires are nutted together in the back of the box. The three ground wires are twisted together. He has two of the black wires twisted together with a third jumper wire. You can see those on the right side of the photo (I removed the taped up wire nut already). The third black wire coming out of the wall (I moved it off to the left in the photo) was just left in the box. It is not hot.

To correct this, I am going to assume that the feed for the lights is off to the left and he has the load feed wrapped in with hot wire and jumper. So all I would need to do is wrap the jumper to one of the light switch screws and the black wire off to the left to the other screw. If that doesn't work, then I bet he messed up and wired in the light feed with the hot instead of the load feed. Am I on the right track here?
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Old 09-16-2013, 11:19 AM   #2
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Light Switch wiring


If I'm following you correctly, your logic sounds spot-on.

Of course, one never knows what crazy wiring one will find in a house. AMHIK

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Old 09-16-2013, 12:08 PM   #3
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Light Switch wiring


I would have assumed the other way around, especially since you state that the left wire is NOT hot. I would have assumed that the feed is part of the two-black bundle, with one wire being unswitched hot, and the other a continuation of the feed to another switch or device.

Of course, I would never wire based upon assumptions. Things are generally not too hard to confirm with observation and a volt meter.
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Old 09-16-2013, 12:47 PM   #4
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Light Switch wiring


So when two of the wires are NOT hot and I want to figure out which is the light fixture feed and which is the load feed that goes on to the rest of the circuit, how would I test to determine the difference? I do have a meter...
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Old 09-16-2013, 12:49 PM   #5
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Light Switch wiring


Also, do I want the light feed wrapped in with the hot wire and then jumped to the switch screw and the load feed tied into the other screw or vice versa?
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Old 09-16-2013, 01:02 PM   #6
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Light Switch wiring


There are devices called Fox and Hound wire tracers, but I'm not sure you'd want to spend the $$$ for one of those unless you plan on doing more of this. You only have two choices for load wires...one to the light and one to the rest of the circuit. Try it both ways and maybe you'll get lucky the first time.
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Old 09-16-2013, 01:03 PM   #7
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Light Switch wiring


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Originally Posted by Eagle One View Post
So when two of the wires are NOT hot and I want to figure out which is the light fixture feed and which is the load feed that goes on to the rest of the circuit, how would I test to determine the difference? I do have a meter...
I would pull all the wires apart, then measure voltage of each relative to neutral or ground. I assume you will find one that is hot, and the other two not.

Next, I would (carefully) touch each of the other two wires to the hot. When the light fixture goes on, you have identified the load.

Next, I would inspect possible outlets or other light fixtures to identify which have ceased to work as a result of having all these wires disconnected. That would be the continuation of the circuit.

If unable to identify load and continuation, then it is possible that original assumptions are incorrect.

Of course, this requires a bit of care to be safe. If uncomfortable with this approach, then other methodes exist, but are a bit more time-consuming and require the removal of the light fixture for access to the wiring at that location.

Quote:
Also, do I want the light feed wrapped in with the hot wire and then jumped to the switch screw and the load feed tied into the other screw or vice versa?
Yes, not vice versa. Feed is unswitched (continuous) hot. The assumed continuation of the hot must also be unswitched, so these need to be tied together. I believe it is a bad idea to try to connect two wires to a singe switch screw, so adding the jumpter wire to the other two, then to the switch screw is a better solution.

Fixture load would be tied to the second switch screw (SWITCHED hot).

BTW...I think it is quite possible that the wiring is correct as is, except for the lack of a wire nut and switch.

Last edited by oberkc; 09-16-2013 at 01:07 PM.
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Old 09-16-2013, 01:14 PM   #8
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Light Switch wiring


As an aside, it certainly makes me curious why the switch was removed. One possibility that comes to mind is that the switch was, simply, failed. Another possibility, however, is that there was a failure in one of the downstream devices. I would probably check resistance between all blacks and ground, and between neutral and ground, just to be sure. Of course, these checks are with circuit de-energized.
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Old 09-16-2013, 01:25 PM   #9
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Light Switch wiring


Quote:
I believe it is a bad idea to try to connect two wires to a singe switch screw
It is not only a "bad idea", it is a code violation. For it to be permitted, the screw terminals would have to be identified as accepting 2 wires.
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Old 09-16-2013, 01:31 PM   #10
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Quote:
It is not only a "bad idea", it is a code violation.
Yes, I understand the same. That is one of the reasons I consider it a bad idea. For me, however, "bad idea" trumps "code violation". Some things I find to be a bad idea even if code compliant.
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Old 09-16-2013, 02:51 PM   #11
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Light Switch wiring


[QUOTE=oberkc;1242381]As an aside, it certainly makes me curious why the switch was removed. /QUOTE]

Yeah, I was wondering the same thing. I was thinking that he wired it up incorrectly and could not get the light switch to work so he just gave up on it. The guy had wired up receptacles incorrectly as well - put the black wires on the silver screws on half of the receptacles in the basement! I had to rewire a lot of them. I don't know what to think but it seemed like he was doing a lot of stuff backwards!

As you said however, it may already be wired up correctly so I am going to try to hook up the light switch and see if it works. If it doesn't, I will reverse the feeds and try that.
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Old 09-19-2013, 12:05 PM   #12
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Light Switch wiring


Ok, I fixed the light switch issue. As it turns out, the wiring as it was already set up was correct and the switch functioned properly. I am still not sure why it wasn't there to begin with. Maybe the guy just never got back out to the hardware store to get a new switch?

To recap and confirm my understanding of all of this, there are three black wires coming out of the box. One is the hot from further upstream, one is the light fixture and the last one (call it the load line) carries the current further downstream in the circuit. So, the wire hanging on the left must have been the light fixture one and he had the hot and load tied together. In general, for single pole light switches like this, the hot and load go to one screw (via a jumper wire) and the fixture (whatever it may be) wire goes to the other screw.

Is my understanding of this correct?
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Old 09-19-2013, 04:43 PM   #13
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Light Switch wiring


Quote:
Is my understanding of this correct?
Yes, I believe you are. However, I tend to think of the fixture as "the load", and what you describe as the load I think of as a "continuation" of the circuit. Neither, probably, are terms used by folks who know what they are doing.

Hopefully, someone can offer proper terminology for our future reference.

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