bad 3 way switch?

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  #1  
Old 02-19-12, 05:33 PM
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bad 3 way switch?

I am adding a three way switch circuit at my stairs. All wires are run to a single junction box, I've wired the circuit through one switch not through the light first. When I tested the circuit the light is half on, when I hit the switch it goes to full bright and if i hit the other switch it goes back to half bright. I checked all the wire connections (twice) and replaced the light fixture with a different one and had the same results. Is this a bad switch? I reused some from my box of parts...or have I messed something else up...oh the circuit in general also connects to two outlets, again fed from the same central junction box.

thanks for your input!
 
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Old 02-19-12, 05:40 PM
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Sounds like you have something in series.

I am adding a three way switch circuit at my stairs. All wires are run to a single junction box,
Do you mean you have a 3-conductor cable from each switch, a 2-conductor cable from the light, and a two conductor power cable in this box?
 
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Old 02-19-12, 06:06 PM
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When I tested the circuit the light is half on, when I hit the switch it goes to full bright and if i hit the other switch it goes back to half bright.
I suppose you could have a bad switch, but I have seen this happen before in old homes (like 60-80+ years old) when the polarity was reversed.
 
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Old 02-19-12, 06:37 PM
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Pull the fixture and carefully put your multimeter test leads on the fixture s black/white wires and see what voltage you are getting to the fixture while it is on . It sounds like you are switching the neutral and it is backfeeding just enough to power the fixture bulb filament.

P.S. I am assuming here that since you have taken it on yourself to run a three way switch circuit, you are skilled enough to work with live voltage. If you are not comfortable testing live wires, then DONT do it ! Be Safe !!
 
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Old 02-19-12, 06:40 PM
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ray-yes i have 3 wire to each switch, two wire power in and two wire to light. The circuit also has two two wire conductors going to two different outlets, one of which is a gfci, these are connected from the power in line. I guess i need to rearview parallel and series circuits!

thanks casualjoe, the house is less than 20 years old but I'll think on the polarity, the outlets were working fine before I added the light.
 
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Old 02-19-12, 07:32 PM
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thanks casualjoe, the house is less than 20 years old but I'll think on the polarity, the outlets were working fine before I added the light.
The only example I could remember was long ago in a very old house, but I suppose this could also happen in a not so old home as well. What greg mentioned about a switched neutral could be the same thing as polarity reversal. If you have a meter, you could check your neutral conductors (white wires tied together in the switchbox)to ground, if you get 120 volts you have a polarity reversal and are switching the neutral on the black conductors. If the polarity is not reversed, you could be accidentally switching the white neutral conductors instead of the black hot conductors. Does that help or did I confuse you?
 
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Old 02-19-12, 08:53 PM
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thanks CasualJoe & greg, I'll test at the fixture and test the polarity tomorrow and let you know how it goes. Luckily I decided to check the circuit before we close up the second switch behind drywall!
 
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Old 02-20-12, 02:59 AM
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When I said that he may have a "switched neutral" I meant that lierally, as in he may be breaking the actual neutral conductor in his 3 way switch circuit so the bulb is finding a nuetral by backfeeding though the receptacles, that may have a table lamp plugged in to them. Open or poorly connected neutrals cause very weird and bad outcomes.....

Breaking neutrals happens sometimes even with pros depending on what location they power the first 3 way. Because the white conductor in the 3 wire romex cable becomes a "hot" conductor in the two traveler wires, so if it is not marked in a junction box, sometimes it gets put in the switched circuit accidently. ...

The OP did not state what bulb he is using, but if it is a incandescent, polarity will not matter to it. Polarity is important in fixture wiring so the outside threaded part of the lamp socket is not energized (shocking to the bulb changer !) . The outer threaded shell of the bulb socket shall be the grounded conductor( neutral) If it is a CFL lamp, they may have diodes in them and polarity is important.

The OP needs to start at the fixture with voltage checks and go to his receptacles and check voltages. If he isnt getting 115-120 volts, then he has wiring connection problems. I have never purchased a bad new, 3 way switch, but that doesnt count anymore....

If the OP doesnt have a MM with ohmeter/continuity check capabilities to test the 3 way switches internal actions,then he might want to pick up some new switches. From where I an sitting (ha) if appears to be a wiring issue..

The OP can also google " Three way switch wiring" and the sites listed have actually pics of all the different 3 way switch wiring configurations. good luck OP.
 
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Old 02-20-12, 10:23 AM
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Thanks greg, I'll google the wiring diagrams...I keep going over my book & the circuit I drew and must be missing something. I'll also check the other outlet wiring, the GFCI outlet tests fine.
I found 25v across the fixture (incandescent bulb fixture, very simple plain jane fixture) I found 0v across the white neutrals to the grounds in the junction box. I'm guessing its my wiring, but since I did use one new switch and one old from my box of spares and I have to go to the store anyway today so I may get a new one just in case.

Thanks, Claire
 
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Old 02-20-12, 11:08 AM
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ray-yes i have 3 wire to each switch, two wire power in and two wire to light. The circuit also has two two wire conductors going to two different outlets, one of which is a gfci, these are connected from the power in line.
Then it should be wired as follows at the Jbox..

Black of power in connected to black of power out, and common to one switch. (Common is black screw.)

Black of light to common of other switch. (Common is black screw.)

Traveler A from switch 1 to traveler A of switch 2. (Brass terminal is traveler)

Traveler B from switch 1 to traveler B of switch 2. (Brass terminal is traveler)
(It doesn't matter which traveler terminal on Switch 1 goes to which traveler terminal on 2)

The neutrals tied together. Note the whites of the two 3-conductor cables are not neutrals and used either as common or travelers.

All grounds together and to the box if metal.
 
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Old 02-20-12, 11:23 AM
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Okay, so the plot thickens.

I googled three way circuits, found exactly what I'd done..in the wiring diagram marked "correct." I checked the outlets both were fine with correct voltage, still thinking they were the culprit I disconnected both from the circuit and still got the light half on, 25V across the fixture. I then realized the bulb was an LED looking like a standard incandescent. I swapped out the bulb for a real incandescent and low and behold 0V across the fixture switches work. I then reattached the outlets and the circuit works like a charm.

Now I'm wondering what's up with the LED bulb? How is it so different that it allows current across when the power is switched off? Can I only use Incandescents on this circuit with this fixture? Note the fixture I was testing the circuit with is temporary, the final intended light source is an LED handrail.

Thanks again everybody for your help! My husband's confidence in my wiring has been restored!
 
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Old 02-20-12, 04:18 PM
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Way to go !

LED's come in all different styles and some are low voltage, some are 120 volt. Those with diodes in them will be polarity sensitive. You could have a LV LED or if it is a 120 volt LED, the polarity could be reversed at the fixture. As I said above, a incandescent bulb doesnt care about polarity. Check your polarity at the fixture wires with the fixture removed. ...

Put one lead of your V- meter on the black wire that goes to the fixture, touch the other V-meter lead to equipment ground bare /green conductor( hopefully you have a operative ground) .

It should read 120 V. If it doesnt, do the same with the white wire, if it reads 120 V to ground, you have the polarity reversed, which is unsafe and will make a LED bulb freak out. Trace your wiring back to see if the black/white got reversed and correct it and you should be lit up properly. oops, not a good use of words when doing electrical work ) good luck
 
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Old 02-20-12, 05:40 PM
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LED's come in all different styles and some are low voltage, some are 120 volt. Those with diodes in them will be polarity sensitive. You could have a LV LED or if it is a 120 volt LED, the polarity could be reversed at the fixture. As I said above, a incandescent bulb doesnt care about polarity. Check your polarity at the fixture wires with the fixture removed. ...
An Led in itself is a diode. Also, there is no polarity in AC, as it changes 60X/second.
 
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Old 02-20-12, 07:37 PM
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Also, there is no polarity in AC, as it changes 60X/second.
Technically speaking, you are correct, polarity refers to DC circuits which have a Positive and Negative conductor. The term polarized or reverse polarity, however, has become an accepted term in the electrical industry to mean hot neutral reversal on AC circuits. Look at this page from the Leviton catalog:

115PV > Plugs > Straight Blade Wiring Devices > Electrical Wiring Devices > Products from Leviton Electrical and Electronic Products

As a wiring device manufacturer, Leviton uses the terms polarity and polarized in this example to mean the hot and neutral sides of the male plug cannot be inserted in the matching female receptacle incorrectly causing a hot neutral reversal.

Brand Features

Leviton Plugs and Connectors are rugged and easy to wire. They are offered in polarized and non-polarized versions and in all NEMA configurations
The picture shows a non-polarized plug which can be inserted into a matching receptacle incorrectly causing a hot neutral reversal.
 
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