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Old 02-17-2014, 08:41 PM  
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I won't add anything but to say them things have always confused the hell out of me!



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Old 02-18-2014, 06:14 AM  
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I think you might have a high impedance meter and it’s leading you to reading all these phantom voltages. A good general purpose multi-meter with lower impedance should not be reading these. Most people doing home wiring will not be testing transistors and such.


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Old 02-18-2014, 06:42 AM  
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Quote:
Originally Posted by havasu View Post
I won't add anything but to say them things have always confused the hell out of me!

A 3way and 4way switch shouldn’t be confusing but for most people they need to see it in schematic form and then the light comes on for them. Pun intended. There are 100s of drawings on line that show pictures of switches and wire nuts and light bulbs. They are correct but they do confuse until you see what is inside the switch and how the terminals are arranged.

A normal switch opens and closes a circuit. A 3way switch never opens the circuit it redirects it. Picture a water valve on the end of a hose and the normal switch stops the water. The 3way switch can never stop the water it has two openings for the water to come out A and B.

It takes two of them working together to work and that is where seeing it in schematic form clears it up for most people. Wuz attached a google search link to his post and if you follow it shows page after of the wire nut pictures and a few with schematics. Here is one that shows it both ways.
http://hometoys.com/emagazine.php?url=/htinews/dec97/articles/kingery/kingery6.htm
No need to read past Fig 2. and it’s a good explanation up to that point on 3way control.

Figure 2 on that page is as simple as it really is. The arrow is the switch SPDT (single pole double throw)The black and red are what they call the travelers and the white is the common wire.

If you had two A/B valves and a sprinkler where the light bulb is you turn on the sprinkler from two different locations.
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Old 02-18-2014, 08:20 AM  
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Quote:
Originally Posted by bud16415 View Post
I think you might have a high impedance meter and it’s leading you to reading all these phantom voltages. A good general purpose multi-meter with lower impedance should not be reading these. Most people doing home wiring will not be testing transistors and such.
A low input impedance meter, like 1000 ohms/volt (1 mA full scale reading for the meter movement) will give you very confusing readings.
The low impedance meter needle stays on the same place on the scale because the current is constant no matter what range you're on, so you might see 50v on the 150v scale (0.3 mA) and then 17v on the 50v scale (0.3 mA) and then 5v on the 15v scale (0.3 mA).
It's because the phantom voltage, 120v in series with thousands of ohms of capacitive reactance from the conductors being close together, acts like a current source rather than a voltage source. Readings like above confirm you are not measuring a voltage source.

With a high impedance meter, the readings are more or less constant regardless of the range you're on, but slightly less than 120v.

Wall outlets and batteries act like voltage sources while LED drivers and fluorescent ballasts act like current sources.



BTW, if the wire colors in the OP's setup are not to code there is still a way to figure out where each one goes, either using an ohmmeter or
an extension cord connected to a known good outlet and a test light or meter.
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Old 02-18-2014, 08:43 AM  
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If anyone wants to know more about ghost voltages and dual impedance meters and what range would be best here is a good read by Fluke.
http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/electrical/dualimpedance.htm

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Old 02-18-2014, 12:29 PM  
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The 10K meter Fluke talks about in the link would read about 2% of 120v, assuming you had 50' of two-wire-without-ground Romex.

A cheapie meter on the 150v scale would have 150K of input resistance but the Wiggies had about 4K.

Help Fluke go bankrupt by getting your 100W bulb with your existing meter!

Fluke also makes a very expensive ground fault leakage current tester.
You can do the same thing by getting a $15 GFCI, disconnecting the internal relay and picking a voltage off of the internal IC that is proportional to leakage current.
With the schematic of the insides of the GFCI's IC (probably on the Web) this should be easy and there is at least one GFCI in my basement waiting on this surgery.
Even if the GFCI no longer works the IC may still be good.

One thing that is not easy for a DIYer is to duplicate one of their ground resistance testers.

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Old 02-18-2014, 12:39 PM  
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Bud and Wuzzet: Nice; how about instructions on what to check and what you are looking for and what it will tell you after you have found it and what to do about it.
I'm not sure what a test light will tell you that the ceiling light won't tell you. Likely all he has done is mix up two black wires or a black and white on the left side of one of the switches.

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Old 02-18-2014, 01:08 PM  
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That’s what I was trying to do in #13 the problem is without understanding how something works first and even havasu a long time poster admitted he is often confused by them. I posted in first again with a worry of advising someone to use a light bulb in a socket and two wires as a test device for voltage. There are a number of voltage testers for under 50 bucks some under 10 that are safer and do the same thing only better.

To talk to the OP about wires is pointless unless he understands the concept first. I have seen 3ways wired up using 3 conductor wire red, black and white and I have seen them using 2 cables each with a black and a white. I have also worked on them with 3 knob and tube wires. If he had a working 3way and it stopped working and he changed each switch wire by wire as I think he claimed he should have been ok. But I believe Neal is correct he got something messed up along the way and now has to figure out what he has. Where he gets power and so forth. Before he does that IMO he should know how a 3way actually works in theory.

I agree all this phantom voltage talk just muddies the water.

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Old 02-18-2014, 01:16 PM  
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On re-reading the first post, this could be a loose wire nut at the light, or back to critters again.

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Old 02-18-2014, 01:25 PM  
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Quote:
Originally Posted by nealtw View Post
On re-reading the first post, this could be a loose wire nut at the light, or back to critters again.

It could be anything.


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