One of the kitchen lights was flickering and there was noise
coming from the switch when the light was flickering. I removed
the cover, preparing to replace the switch.
Before doing anything, I first measured the voltage. The voltage
between the bottom (hot) black wire and ground was 110 V. That's
what it should be. When the switch was in the ON position, the
voltage between the two black wires was 0 V. That's what it should
be. When the switch was in the OFF position, the voltage between
the top black wire and ground was 0 V. That's good.
However, when the switch was in the OFF position, the voltage
between the two black wires was between 86 and 88 V (the reading
kept changing.) This switch was in a 3 gang box. The other two
switches all had 110 V between the two black wires.
About a month ago, I had another light problem in the bed room.
And the voltage between the two black wires was also around 88 V.
Why isn't it 110 V?
Welll, for starters it should probably be 115 volts or higher. The
latest standards, I believe, call for 120 V nominal, 115 - 125 V are
to be expected. The much lower voltage measured across the switch
shows that something is partially shorting out inside the switch, and
the other readings are normal. You can get a replacement switch for
as little as 39 cents at a big box, just try it. Then, with the old
swich, if you can measure ohms, you may see only a few hundred ohms
across the switch contacts that are supposed to be infinite ohms on
open/off. But the multimeter you will probably use to measure the
ohms uses only a couple of volts to measure the ohms.resistance, and
if it is dirt or insects or something else breaking down inside the
switch, that breakdown may not occurr until there is a much higher
voltage presented to the switch, and it may look ok when you measure
it. If so, you can waste time trying it out again, but I would toss
it into the garbage or recycle bin.
Except he took that reading with the switch open, which means he's
reading from hot, through the light to ground, and the switch is not
in his circuit.
If this is a fluorescent light and especially if he's using a digital
meter also, the reading is suspect at best.
John, the best way to test the circuit and the possible failure modes
will depend on the type of light you have (incandescent, compact
fluorescent, fluorescent tube). If it's a compact fluorescent,
temporarily replacing the bulb with an incandescent bulb will make it
easier to debug.
You are measuring voltage with the lamp in the socket in series.
Maybe you have bad socket(arc'd, oxidized, or tarnished or plain loose
contacts inside the socket). How old is your house? Any Al wiring?
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