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Old 04-25-2010, 04:49 PM   #1
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3-way switch setup tests dim and bright but never off


Greetings,

In my older house (1950's) a three-way light switch setup has never worked. I attempted to fix it with two new three way switches, wired as shown in the attached diagram.

Using a neon tester with the four different combinations of switch positions, the tester lights dimly in two situations and brightly in two situations. It NEVER remains unlit.

I'm concerned something is wrong, so I have not yet attached the light fixture.

Is this in any way normal?
Advice on how to troubleshoot from here?

Thanks,
Paul
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Old 04-25-2010, 06:49 PM   #2
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Attach the light fixture and see what happens.
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Old 04-25-2010, 07:33 PM   #3
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Nothin' wrong with the diagram, if you connect the lamp no harm will come from it!
The worst case would be that the breaker will trip! If it trips you will know that the wiring is wrong or there a fault with the wiring! A short circuit?
Neon testers can be confusing and are OK for testing for the presence electrical potential. Its best to use a volt meter, for trouble shooting!
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Old 04-25-2010, 07:39 PM   #4
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Quote:
Originally Posted by paulekaiser View Post
Using a neon tester with the four different combinations of switch positions, the tester lights dimly in two situations and brightly in two situations. It NEVER remains unlit.
Chuck that neon tester unless you want to use it as a nightlight.
For house elec. you need a low input impedance voltmeter [a Wiggy] or a regular voltmeter loaded down with an incand. bulb or resistor.
Troubleshooting is hard enough without your test instruments leading you astray.

To test your setup without sparks and drama, put an incand. lamp is series with the AC source. The controlled lamp and this lamp should be the same wattage.
If all works as planned both lamps will glow dimly when the controlled lamp is switched on. If there is a short the series lamp will be at full brightness; you can then troubleshoot the setup without breakers tripping and switch contacts being overstressed.

Last edited by Yoyizit; 04-25-2010 at 07:44 PM.
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Old 04-25-2010, 07:39 PM   #5
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maybe lose neutral wire. Tighten the neutral/white wire more tightly.
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Old 04-25-2010, 09:45 PM   #6
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Connect up the light fixture.

The diagram looks correct.

I do not think there is any problem with the neutral.

3 way switch setups are very likely to make neon testers behave the way you described. In the "dim" condition the 3 way is off; one traveler is connected to the hot feed and the other traveler is connected to the light fixture with no direct connection. But because the two wires run next to each other for several feet of distance in the same cable, there is a minute amount of current leaking between the two conductors, right through the insulation, enough current to light up the neon tester slightly.

If you were going to get sparks and fireworks due to a short circuit you would already have gotten them by now. Connecting up the light won't start the sparks.
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Last edited by AllanJ; 04-25-2010 at 09:55 PM.
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Old 04-26-2010, 10:34 AM   #7
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Thanks all - issue solved!


Thanks for all the replies, and especially the explanations that neon testers have their place, but aren't foolproof. I especially appreciate you confirming what I wondered... about the 3-way setup and the travelers goofing up the neon tester.

I simply tested the setup with a little incandescent night light, and found everything to be ship-shape. Now I'm ready to hang the fluorescent and be done!

Take care all,
Paul
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