JoeSpareBedroom wrote:
"Jeff Wisnia" wrote in message
et...

CWLee wrote:

My son recently replaced two wall on-off switches with
dimmer switches, new from Home Depot or Lowe's, for me.
They work fine and control incandescent lights. He
discovered, however, that even when completely off about
48-50 volts still flow through the new dimmer switches -
both of them.

We are both puzzled. We assumed that off would mean zero
volts. If this is normal isn't it a safety hazard?

Any insight appreciated.


40 or 50 volts is enough to make incandescent bulbs glow. Are the bulb
loads connected, and if so, do they glow?

If the loads aren't connected I'm guessing you have a limited knowledge of
electronics and are probably measuring the output of those dimmers with an
electronic (digital) voltmeter which is responding to miniscule leakage
currents that give you what's known as "phantom" voltage readings.

If connected bulb loads "turn off" OK, fughedit.

HTH,

Jeff


That digital meter thing - is it only an issue with AC current?



That depends on how those microamp sized currents are being coupled to
the meter.

On AC, just capacitive coupling between two nearby insulated wires will
cause current flow into the meter through the charging and discharging
of the interwire capacitance. That current develops a voltage across the
meter's input impedance which gets displayed. But, there coan also be
resistive coupling of AC through badly degraded insulation on very old
wiring, or through a film of moisture condensed across an insulating
barrier.

On DC circuits capacitive coupling is not a factor, except perhaps for a
momentary "blip" of the meter when an adjacent wire is powered up or
down, but the resistive coupling mentioned above could easily cause a
significant DC reading on a high input impedance meter.

My "rule of thumb" when encountering those unexpected low voltage
digital meter readings is to put my thumb and forefinger across both
meter probes while they are connected across the circuit. If the shunt
resistance of my hand causes the meter reading to drop significantly, I
know it's nothing to worry about.

YMMV, and to be safe, make sure you're not standing in a puddle or have
your other hand on something grounded if you try that.

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"Rudeness is the weak man's imitation of strength."