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bhalp:
He tested the wires and on one of the wires it read 120v to ground with the dimmer in off position and 120v to ground in on position.
What was the tester? Probably the Ideal Volcon selenoid tester mentioned later. What is the DC input resistance of this tester, and its input AC impedance at 60 Hz? What reading to ground was obtained from the other wire? Also what do ON and OFF mean? Min and max setting of the dimmer, or operation of a mechanical SPST switch in the dimmer? Was there any other switch that controlled this circuit? It does appear that the dimmer was not in series with the hot lead, but rather in the neutral lead. With a high impedance meter and measuring relative to ground a voltage reading of some value on the second wire would have provided more information.
there was only 2 wires in the fixture box. between the 2 wires there was no voltage reading in on or off position.
Did he have a high impedance meter, or only the Volcon? With a two wire dimmer, input and output, there must be sufficient current thru the load to provide power to the electronics in the dimmer for the dimmer to turn on. This means sufficient drive current to the control element of the electronic switch, likely the gate of a Triac. If sufficient current does not exist, then only leakage current flows.
My diagnosis over the phone was reverse polarity and the not getting a voltage reading between the 2 wires i think was because he used an ideal volcon selenoid tester and the dimmer was an old rotary type, which might not have allowed enough voltage for the volcon tester to read but enough for the fixture to work. any thoughts on this situation. never came across this before.
I agree the dimmer was probably in the neutral.
You need to run some experiments with a dimmer comparable to the one with which your friend was working. A new rotary is not necessarily the same as one 40 years old. Note: a rotary vs a slide or other adjustment means does not mean the characteristics of the power switch, Triac, in the dimmer are different.
My quick experiments with a Leviton rotary dimmer. Meter is a Fluke 27 with 10 megohms input resistance, little inductance, and 35 pfd input capacitance in parallel with the 10 megohm resistance. I do not know if this Leviton dimmer uses a Triac or some other solid-state switch.
This Leviton dimmer appears to have a mechanical on-off switch. No load on the dimmer except the meter and 122.7 V AC input.
122.0 output voltage with dimmer switch ON, dimming position of no importance.
4.35 V in OFF position.
This means very low capacitance and leakage in the off position of a mechanical switch, and definitely a mechanical on off switch.
With a 5,000 ohm resistive load the dimmer functioned to adjust the average output voltage. In other words this was sufficient holding current for the dimmer to function. It even worked as a dimmer at 10,000 ohms load.
With a small Potter & Brumfield relay as the load, about 2500 ohms resistance and some moderate inductance, the dimmer still functioned as a dimmer.
I do not know the input impedance of the Volcon. This could be much more inductive than the P&B and might not provide sufficient holding current for the dimmer. Also the dimmer setting might have an effect on the dimmer operation with a highly inductive load. Were high and low dimmer settings used in the test with the Volcon?
The experiment you need to perform is with a Volcon and DVM in parallel fed from a dimmer comparable with what was at your friend's job. That may be hard to do if the dimmer was made many years ago. See if you can reproduce your friend's results. Then add in parallel with the meters 5000 ohms and see if the dimmer has a normal function.
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