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Old 04-16-2009, 01:58 PM   #1
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Replacing light switch in series wired home - help!


I recently purchased a motion detection light switch for our bathroom to help my toddler.

While trying to install it, I noticed that I wasn't dealing with a typical light box.

The old switch (which was clearly installed during construction) has 3 BLACK wires, one which is secured to a screw on the switch and the other 2 come out the back of the switch. All 3 wires seem to be "hot". 2 go together and one is separate. On top of that, there are 3 additional wires that are white that come from the same locations as the BLACK wires in the box, but are just joined together with a cap - no purpose noted.

I successfully installed the new switch by assuming one of the wires must be neutral and attaching it to the GREEN wire that came with the new switch, but much to my dismay, now 3 switches in the bathroom and one in an adjacent room don't work. After replacing the old lightswitch in the same configuration it was in, the switches work again, but only when the original switch is turned ON (which is not the way the switch operated previously).

Any suggestions/ideas? Burn the house down? Live by candlelight? Both seem pretty viable to me at this point after about 50 trips to the breaker box to uninstall/reinstall this dang switch.

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Old 04-16-2009, 02:10 PM   #2
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Replacing light switch in series wired home - help!


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Originally Posted by kellykate View Post

I successfully installed the new switch by assuming one of the wires must be neutral and attaching it to the GREEN wire that came with the new switch, but much to my dismay, now 3 switches in the bathroom and one in an adjacent room don't work. After replacing the old lightswitch in the same configuration it was in, the switches work again, but only when the original switch is turned ON (which is not the way the switch operated previously).
I hate to sound cold, but you have no idea what you are doing. When this is the case even the simplest task can cause bigger problems.
WHY would you assume one of the wires was a neutral????? And green is ALWAYS ground in AC building wiring.
Also, you home is not wired in "series".

One of the black wires is the hot feed. One of them is also a constant hot but a feed out to another area (obviously feeding the other switches). These two get spliced together and connect to one of the wires on the switch. The other black is the switch leg to the light itself, and that goes on the other black wire on the switch. Does the switch require a neutral connection?

Since you did not know what these wires did when you installed the sensor now you have to identify each one so you can correct this mess.

Do you have a decent tester? Voltage and continuity?

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Old 04-16-2009, 02:24 PM   #3
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Replacing light switch in series wired home - help!


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I hate to sound cold, but you have no idea what you are doing. When this is the case even the simplest task can cause bigger problems.
WHY would you assume one of the wires was a neutral????? And green is ALWAYS ground in AC building wiring.
Also, you home is not wired in "series".

One of the black wires is the hot feed. One of them is also a constant hot but a feed out to another area (obviously feeding the other switches). These two get spliced together and connect to one of the wires on the switch. The other black is the switch leg to the light itself, and that goes on the other black wire on the switch. Does the switch require a neutral connection?

Since you did not know what these wires did when you installed the sensor now you have to identify each one so you can correct this mess.

Do you have a decent tester? Voltage and continuity?
The mess is corrected, wires have been connected to existing switch which works. I understand the premise of how light switches work. It does make sense that the 3rd wire would be the hot line out to the other switches. What I can get from your post is that I basically need to find a grounding spot for the GREEN wire and splice the two black wires that come from the same location in the light box together to successfully use the new switch. It does NOT require neutral wire, just grounding.

2nd: there is clearly some sort of series wiring going on since light switches in the same room and next room will not function without the original light switch being turned on (unless there is a name for that description that I am unaware of).

Anyway, I may not be an expert but I'm also not a complete idiot - I was looking for answers, came here. Thanks for your help

Last edited by kellykate; 04-16-2009 at 02:31 PM.
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Old 04-16-2009, 02:47 PM   #4
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Replacing light switch in series wired home - help!


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2nd: there is clearly some sort of series wiring going on since light switches in the same room and next room will not function without the original light switch being turned on (unless there is a name for that description that I am unaware of).
Well it seems like series wiring but it is parallel, for what it's worth. Fact is series and parallel are useless terms in AC building wiring. Circuits and receptacles are ALL wired in parallel. Switches, since they break a line are technically wired in series with the hot line.
Again, this really means nothing and usually only serves to confuse folks who are not familiar with this stuff.

Like I said, you have the feed out to the other switches wired to the load side of the switch. You need to identify this wire and put it on the same side of the switch as the constant hot.
There is a not too difficult way of checking this. Do you have a meter??
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Old 04-16-2009, 03:15 PM   #5
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Replacing light switch in series wired home - help!


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Like I said, you have the feed out to the other switches wired to the load side of the switch. You need to identify this wire and put it on the same side of the switch as the constant hot.
There is a not too difficult way of checking this. Do you have a meter??
Sure do.
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Old 04-16-2009, 05:36 PM   #6
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Replacing light switch in series wired home - help!


Since the new switch now controls the other room and the light, we know that the single black wire is the hot one. Take one of the two blacks and move it to the connection with the single black. If the light comes on and the other room is still controlled by the switch you picked the wrong wire. Switch it with the other one.
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Old 04-16-2009, 06:37 PM   #7
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Replacing light switch in series wired home - help!


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Originally Posted by kellykate View Post
The old switch .....has 3 BLACK wires, one which is secured to a screw on the switch and the other 2 come out the back of the switch.

Any suggestions.......this dang switch.
Kate, from your description, I assume your switch wiring was similar to this pic.

The wires that come out the back of the switch are pushed into spring loaded connections. To release the wire from the switch there is a small rectangular opening right next to the wire. Take a small slot screwdriver and firmly push the tip into that rectangular opening while at the same time pulling to release the wire.

The push-in wire connection closest to the screw, and the screw, both go the same pole inside the switch. This is done to make it easier for the Electrician to install the switch. For the DIYer it may be easier to use the screw terminals.

When installing the original switch the Electrician connected the AC and the AC Feed wire to one pole of the switch using both methods. I show the AC Input connected to the screw, but it is the same if reversed, i.e. the AC Input can be the push-in wire.

I hope this illustration helps with what Speedy and joed have said.
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Last edited by PaliBob; 04-17-2009 at 10:49 AM. Reason: sp
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