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Old 06-25-2011, 04:27 PM   #1
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2 way switch mystery.. no power at switch but power at light when turned on


so i have this 2 way switch, connected to a 3 way wire that i'm having a hard time seeing how it's connected.

since i can't find another switch in the house that turns the light on and off, i figured its a simple 2 way connection. using a volt meter, i test for power with switch on and off and it works perfect aside from my gripe that it's connected via a 3 way wire (red not used). anyhow, i take off the switch plate and using the same volt meter, both black lines lack power at the switch. WTF.. any ideas?? power was to the black wire for the light btw.

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Old 06-25-2011, 04:40 PM   #2
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2 way switch mystery.. no power at switch but power at light when turned on


Need to go to the other switch & the light, and look at what colors are wired where. You can get something like the Black & Decker complete home wiring guide, which has pretty much every wiring circuit type shown in it to help see how to properly wire. Btw, is this a rented place, or do you own?

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Old 06-25-2011, 04:44 PM   #3
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2 way switch mystery.. no power at switch but power at light when turned on


you wont get any reading from those wires. you need to check between the black and a white or ground. if it was a 3 way switch and replaced with a 2 way the other switch wouldnt work anyway since there isnt a 3 way installed in the one you are checking.
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Old 06-25-2011, 04:57 PM   #4
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2 way switch mystery.. no power at switch but power at light when turned on


so there must be another switch? i don't see another switch for the light outside.

how can a switch power something on when it doesn't have power itself?? i'm going to check the white wires to see if someone switched the wiring inside the walls.
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Old 06-25-2011, 05:22 PM   #5
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2 way switch mystery.. no power at switch but power at light when turned on


it is possible that the red wire is not used, but merely installed for future use(ceiling fan?)
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Old 06-25-2011, 08:29 PM   #6
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2 way switch mystery.. no power at switch but power at light when turned on


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Originally Posted by vote4Pedro View Post
sohow can a switch power something on when it doesn't have power itself?? i'm going to check the white wires to see if someone switched the wiring inside the walls.
Showing that you have power is usually done by measuring voltage. Voltage in lighting circuits has to be measured betwen the place in question and the neutral from the panel out to the utility pole. While a neutral wire accompanies the hot wire out from the panel, not all switch boxes have a neutral line coming into them. A white wire coming into a switch box is not necessarily a neutral wire. You can string a long wire (say, 14 gauge) up from the panel neutral up the stairs and across the floor to where you are working (for testing purposes only), to be the neutral with which you are doing voltage measurements. Measuring between the place in question and ground (a ground wire; grounding conductor) is done by electricians but they have to use intuition, jump to conclusions and take the results with a grain of salt, and experience builds confidence.
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Last edited by AllanJ; 06-26-2011 at 08:27 AM.
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Old 06-25-2011, 09:27 PM   #7
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2 way switch mystery.. no power at switch but power at light when turned on


The power is probably in the ceiling box.
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Old 06-25-2011, 10:42 PM   #8
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2 way switch mystery.. no power at switch but power at light when turned on


If you are using a volt meter, if you read across the switch when the light is on you should read no voltage if you switch the switch off you should read 120 volts. If you read from the switch to ground and can't get a voltage reading you may have old wiring with the switch switching neutral.
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Old 06-26-2011, 01:14 AM   #9
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2 way switch mystery.. no power at switch but power at light when turned on


If it is indeed a two way switch set up,
then the power could be at the other switch!
It is difficult to explain unless you understand
how two way switchs work.
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Old 06-26-2011, 08:21 AM   #10
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2 way switch mystery.. no power at switch but power at light when turned on


Two way switch?? Three way wire?? I think your terminology is wrong.
Testing for voltage in a switch box will require either a true neutral or a ground wire or a grounded box. One meter lead is connected to one of these points and the other to one of the switch screws.
There are three types of switches found in residential wiring:
1) On Off Switch - two screws.
2) Three way switch - three screws.
3) Four way switch - four screws.
The above three examples are not counting a ground screw if present (green).
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Old 06-27-2011, 05:04 PM   #11
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2 way switch mystery.. no power at switch but power at light when turned on


In Australia a two way switch set up is
were there are two switchs controlling one light,
A three way switch set up uses three switchs to control one light,
two way switchs are pretty common,
but three ways are rare.


I was using the term two way switch
to refer to the wiring set up,
not just the switch mechinism
which i think is what you might be refering to.
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Old 06-27-2011, 06:19 PM   #12
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2 way switch mystery.. no power at switch but power at light when turned on


mystery solved. turned out that the wire wasn't done properly in the bare ground wasn't actually grounded. so the black (hot) wire and the ground never completed a full circuit. initially i didn't want to take out to take out the switch to test the white wire but long story short, it's been done and properly grounded.

now for part 2 of the mystery.
4 way wire comes out of the circuit breaker. the black seems to be on the breaker that is labeled (laundry) while the red wire is associated with another breaker(garage). there is just one ground and one white for this setup. is it up to code what they've done? essentially using one 4 way wire to handle 2 breakers?

tx
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Old 06-27-2011, 06:23 PM   #13
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2 way switch mystery.. no power at switch but power at light when turned on


It is not called 4 way wire. As for the Ground not completing the circuit, only if the Neutral (White) is not connected, then yes the ground could complete the circuit. You have 2 wire, and 3 wire, and yes there are some circuits that are 4 wire, which depends on the application that you are doing.

As for the new circuit, it sounds like you have a Multi-Wire Branch Circuit (MWBC), but odd that it would go two different directions. Where are you located Pedro?
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Old 06-27-2011, 06:27 PM   #14
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2 way switch mystery.. no power at switch but power at light when turned on


DC area. my mistake by calling it a 4 way wire. it's actually 4 wires so it's a 3 way wire. i found this box towards the end of the basement so i guess the intent was to split to power to 2 different locations from that wire box. seems like the proper way would of been just to run another full line to the fuse box.
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Old 06-27-2011, 08:19 PM   #15
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2 way switch mystery.. no power at switch but power at light when turned on


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Originally Posted by vote4Pedro View Post
DC area. my mistake by calling it a 4 way wire. it's actually 4 wires so it's a 3 way wire. i found this box towards the end of the basement so i guess the intent was to split to power to 2 different locations from that wire box. seems like the proper way would of been just to run another full line to the fuse box.
No, it's not "3-way wire" either! There is no such thing as "[any number]-way wire". If the cable has two insulated conductors plus a ground, it's called "two conductor with ground". Likewise for any other number of conductors. The presence of a grounding conductor is often assumed, so it's omitted from the count. You do use three-conductor cable to wire a 3-way switch, though.

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