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Posted by RBM on January 25, 2008, 3:48 pm
Every time I read posts where people are testing circuits with a variety of
multi meters, I've been tempted to tell them to chuck the meter and get a
pigtail socket. Like Ralph, and you, I've got all manner of test equipment,
but the pigtail or wiggy tell me everything I need to know, almost all the
time. It's simple and it works
>
>> You need to check voltage from the hot wire on the switch to the two
>> neutrals that are spliced together. If you get 120 v, you have an open
>> neutral between that box and the first lighting outlet. If you don't get
>> 120v, you have an open neutral wire somewhere upstream of the switch box.
> I
>> would check nearby outlets and switches for the bad connection. It could
> be
>> an upstream GFCI, if one exists, but not likely as that would disconnect
> the
>> hot leg to your circuit.
>>
>>
>>
>> >A friend asked me to help her repair her bathroom light switch, which
>> > had stopped working. By the time I got there, she had already
>> > installed a new switch, but it still wouldn't work. .It's a one-way
>> > switch, controlling two wall fixtures.
>> >
>> > The house (which is in the USA) is about sixty years old and has two-
>> > prong plugs, everywhere. The light switch has two screws, with a
>> > black wire to each screw. There are two white wires in the switch
>> > box, spliced together (and they had obviously been that way for many
>> > years). One lamp fixture has two black and two white wires, with the
>> > two blacks connected to the fixture's black wire and the two whites
>> > connected to the fixture's white wire. The other fixture has one
>> > white and one black going to it. So far, so good. Apparently, the
>> > fixtures' wiring is somewhat newer than the rest of the house's
>> > wiring, because they also each have a ground, which is connected to
>> > each box, mounting plate, and fixture housing.
>> >
>> > I couldn't see anything that was obviously wrong. And the light
>> > fixtures and the old switch had been working for years. So I used my
>> > multimeter (Tektronix DMM916) and did some very basic measurements,
>> > but will probably need to go back and do some more. Anyway, here is
>> > what I have measured, so far:
>> >
>> > With the switch on, and no bulbs installed in the fixtures, the
>> > voltage (VAC RMS) across the switch terminals is very low, i.e.
>> > approx .04 VAC. At each fixture, white-to-ground measured 54 VAC,
>> > black-to-ground measured 120 VAC, and black-to-white measured 34 VAC.
>> >
>> > WITH bulbs installed, and the switch ON, both white-to-ground and
>> > black-to-ground measured 120 VAC, and black-to-white measured anywhere
>> > from 14.6 VAC to 18VAC on the first fixture and about .04 VAC on the
>> > second fixture.
>> >
>> > But, after emptying some dead insects out of the first fixture, it,
>> > too, measured .04 VAC from black-to-white. (I neglected to measure it
>> > again, without bulbs, to see if the 34VAC from black-to-white had then
>> > changed.) The black-to-white measurements without bulbs also matched
>> > the measurements between the socket bases and threaded bulb holders.
>> >
>> > With the switch OFF (both before and after emptying-out the insects in
>> > the first fixture), the voltage across the switch terminals (two
>> > blacks) was about 70 to 76 VAC (varied between measurements).
>> >
>> > Also, with the switch off, the resistances, at the fixtures, between
>> > any two of black, white, and ground all appeared to be infinite, as
>> > did the resistances between the socket bases and threaded portions..
>> >
>> > Can anyone figure out what's going on, from that? Or, what else
>> > should I measure, or try?
>> >
>> > Could it be a problem in the breaker box, itself? I did happen to
>> > notice, about six months ago, that her breaker box was open, slightly
>> > (not the door, the whole front panel!). But it appears to be closed-
>> > up OK, now. The breakers look very old, though. Also, everything
>> > else in the house appears to be working as it always has. And that
>> > circuit does not have its own breaker.
>> >
>
>
> In addition to what RBM said, I would suggest that you stop using that
> multimeter and just use a pigtail socket and standard light bulb to test
> the
> wires. The results will be more definitive. All of those odd voltages
> that
> a multimeter displays just confuses a do-it-yourselfer.
>
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