We are suspecting that our 3-way dimmer by Leviton is defective. We
are trying to run connectivity tests with a digital voltmeter, and
very high resistance (1.6MOhms). Perhaps the mechanism in these
devices is such that it cannot be measured with a cheapo digital
By measuring resistance, I'm hoping the detect connectivity b/w the
common and one of the travelers. When I flip the switch, I want to see
connectivity b/w the common and the other traveler. I'm not seeing
that. Defective dimmer?
Something's wrong and I can't post so I'm emailing.
On Sat, 13 Jun 2009 22:48:30 -0700 (PDT), "Jim O'Brien"
One can have no idea from the kind of testing you're doing. There is
a whole little IC chip inside that thing and it won't switch to ON if
it's not connected to 110volts. If you do connect it to 110 volts,
you can't measure resistance without burning out your meter.
The way to do this is to leave the switch fully connected, to all
three wires. You probably have two three way switches. There are a
variety of ways to wire these things, so I'm can't tell you that one
wire will be 110 all the time, or when the light is on. It's more
complicated than that.
But you might get lucky, so I'd measure the voltage btween each wire
and ground. If done correctly the metal mounting flange of the switch
is grounded, or the metal box it's mounted in, if the box isn't
plastic. If any of these voltages are a full 110 volts AC, then one
of the other two should be also. Then when you flip the switch, the
common wire should stay at the same voltage and the other two should
interchange which is 110 and which isn't. If one wire is 110 and
neither position of the switch makes either other wire 110 the switch
is broken. Also if one wire is 110 and an another wire is 110 but
when you flip the switch, only one wire is 110, the switch is broken.
If you don't find 110 at any wire in the switch, do the following:
What I would do then depends on whether you know which wire in that
switch is the common wire.
If you do, I woudl measure the voltage between the common wire and
each of the other wires when the switch is in one position. Then
flip the switch and make the same measurements.
In one switch position, there should be less than a volt or two AC
between the common wire and remaining wire A, and there should be 110
volts between the common wire and the other wire B.
When you flip the switch, those readings should reverse.
If you find over five but under 90 volts somewhere, I'd calibrate your
meter by measuring the voltage at a good receptacle. If it's 110 or
120 there, but under 90 and over 5 at that other location, it's
probalby a phantom voltage that is picked up by your very sensitive
voltmeter, but one which has no ooomph, no power behind it. In a
simple situation like this, you can ignore such voltages in your
logic. Assume they are zero.
If you don't know which is common, I'd make 3 measurements for each
switch position, write them all down and figure out which one is the
commnon and then continue as above.
each pair of wires
On Sat, 13 Jun 2009 22:48:30 -0700 (PDT), Jim O'Brien
The dimmer operates at 120vac and puts out a pwm (chopped) signal to
a bulb. Why, pray tell, do you think measuring its resistance at the DMM's
battery voltage will tell you anything useful? You're measuring the resistance
of solid state devices that aren't switched on.
The only hope you have with a DMM is to connect the dimmer to a load and measure
it then; however, at that stage, if the load is a lightbulb you could simply
look at the bulb's brightness to get the same information.
Too technical, forget the meter. First, if you have a Leviton dimmer, it's a
pos, so just get a Lutron of your choice and replace it. When you have the
existing dimmer out of the wall for "testing", remove it from the three
wires, noting the common wire. Touch the common wire to each of the
travelers. One of the two connections should turn on the light. Flip the
other switch in the circuit, then touch the common to the travelers again,
and this time the other connection should make the lights come on. If things
don't happen as I describe, you have a wiring problem
*I agree with RBM. Throw away the dimmer and stop using a VOM for any house
wiring. Change the dimmer to a three-way switch to see if your problem (You
didn't specifically state what your problem is) is corrected. You must
identify the common wire in the switch box. Don't go by color code.
In general, you can't get any useful information by trying to test for
connectivity/resistance over a solid state device. Among other things
you normally won't get any output unless the device is powered, and
you can't test connectivity/resistance while it's powered. The output
in this case is probably also a fixed voltage over a varying wave
pattern, Who knows what that will look like to a solid-state volt
You would need at least an oscilloscope and an ohmmeter to test it
conclusively. If you had a working one to compare it to, you could
probably get a good idea with a non-solid-state voltmeter and a known
good incandescent bulb.
Agree; forget the meter; with solid state devices any high impedance
meter (including cheap or expensive digital ones) can give misleading
Just use basic fault finding; touch or bridge the connections over
(past the dimmer) to simulate what the dimmer/three-way switch is
supposed to do.
If that doesn't work then there is another problem somewhere.
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