Can't test dimmer with Fluke?

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GerryB

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Location
woodbridge, ct. USA
I know you get phony voltage readings with the fluke and 3-wire circuits, but this was a simple wire in, down to switch (sp dimmer) and back to light. With the fluke, dimmer off, no reading, dimmer on, 119v to ground. With the old wiggy, 0v to ground. I don't recall this always being the case, maybe this particular dimmer?
 
How about if you connect a load to the dimmer then test with a wiggy. Do you get a reading?
 
GerryB said:
... With the fluke, dimmer off, no reading, dimmer on, 119v to ground. With the old wiggy, 0v to ground. ...
Click to expand...

Dimmer is high impeadance ( open. ) Load is also open. Wiggy presents a load which the dimmer is unable to deliver current to. Fluke is a high impeadance input and can easily read a voltage due to small amounts of leakage. Dimmer is leaking enough current to charge up the run and the Fluke and read a voltage. Load is not present to discharge the circuit.
 
To add to what starbolin said, I think you're reading full line voltage because the dimmer is a PWM, and it's not actually reducing peak voltage, it's simply chopping it so the average voltage going to the load is much lower.

My guess is your high impedance meter is just picking up the capacitance generated by those peaks.
 
He's probably picking up the leakage current of the neon (night) light inside since he made reference to one not coming on. Since the fluke is a high resistance meter.
 
I got the same readings with a load connected and with no load. With the fluke 0volts with the dimmer in the off position and 119volts in the on position. No reading either way with the wiggy. New dimmer worked fine. As said it was the fluke, I am just pretty sure I have tested dimmers before with the fluke and not seen this, so those dimmers were apparently working so I didn,t know the difference. I know you see it all the time on mwbc if you turn off one leg. So now I know a defective dimmer can still give you a good reading on that type of tester,
 
big john said:
To add to what starbolin said, I think you're reading full line voltage because the dimmer is a PWM
Click to expand...
The dimmers I've come across are phase controlled. Mostly leading edge but, in some cases, trailing edge.
They work by reducing the conduction angle in each half cycle:

Phasecontrol01_zps42bb743d.jpg

The company I work for makes dimmers.
Not something I have responsibility for - I just get dragged into in when there are problems, usually harmonics.
 
GerryB said:
I got the same readings with a load connected and with no load. With the fluke 0volts with the dimmer in the off position and 119volts in the on position. No reading either way with the wiggy.
Click to expand...

in your first post you said with respect to ground. What do you get if you measure with respect to the load connected neutral? Must not be 119V or the load would be on.
Integrity of the ground?
 
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