I would appreciate assistance in troubleshooting an electrical problem:
I have a single-pole switch serving 3 overhead lights in basement.
All lights are inoperable. I replaced the wall switch (evem though old
one passed a passive test) and same problem. I have 2 wires wires
entering the switch - a 3 conductor and a 2 conductor. The 2 Conductor
appears to be the feed/source. When I separate all wires, I measure
50v across the neutral (white) to the live (black) and measure 110v
between black to ground. It would appear to be a bad neutral feeding
the switch. What is the best way of troubleshooting this circuit
(other lights/outlets on the circuit breaker appear to operate normally
so I can eliminate the circuit breaker as cause).
The 50 volts you are measuring is probably from capacitive coupling
between wires - phantom voltage. If you connected a light from incoming
hot to neutral there would probably be zero volts.
The problem is probably in a neutral connection in another box. Could be
a loose wire in a wire nut or bad contact in a backstab connection
through a receptacle. (I think everyone in this newsgroup advises
eliminating backstabed connections.) The bad connection is likely in a
box with receptacle/light/switch on the same circuit that is closer to
the panel. (Could also be in another dead box, but you said there
Good troubleshooting so far.
I do have many backstab connectors, mainly on the outlets rather than
the switches. I did visually check the nearest ones to the suspect
switch locality for physical problems (loose/burned, etc) but have not
yet replaced them with screw terminal outlets. Is there a proper way
to "test" these outlets rather than a visual test?
Turn off the breaker first then use an ohmmeter to check the continuity
between the wire at the back of the receptacle and the hole for the plug in
Its a wasted exercise though since the act of removing the receptacle from
the j box and pulling on the wires would have fixed an open. if it were
really bad, it should just fall out. Just buy a 10 pack of recepicals at HD
and have at it.
In any case, a map of the path each branch circuit takes on its way from the
breaker box to the receptacles is very useful. Might take the opportunity
to map this branch out and tape it to the inside of the panel.
Fortunately there should be no connections buried in a wall and wires almost
never go open in the middle.
Over the weekend I was able to identify (not 'trace' - as I have no
idea how to trace all circuits w/o schematic) all circuits working off
of the circuit breaker with the faulty circuit. I checked every switch
and every outlet and verified all "good connections". By that I mean
all had tight connections, nothing burned nor any signs of oxidation.
I did find a light switch that was in the proximity of the "faulty
switch" that appeared to be the feed. When I shorted the neutral and
hot wires at the 'faulty switch' location I was able to see the short
while reading across the N/H wires at the other switch location.
However this second switch serves a ceiling light fixture in the dining
room that works just fine. Every light fixture and outlet served by
this circuit breaker appears to work fine except for the light switch
and the 3 overhead lights in the basement that work off this
switch...which I had replaced simply to eliminate it as the potential
cause. Not being in the trade, my primary trouble shooting tool is an
analog Ohm-meter.. . . and the assistance of those on this site.
So, if you connect everything the the way they were, you would measure 50V
at the basement light switch between neutral and hot. If you disconnect the
neutral/hot at both the feeding end and at the light switch, and you short
them at the switch, you meausure zero ohms at the feeding end. Is that an
This doesn't help.
When you connected everything back and measure 50V at the basement light
switch, if you then disconnect the neutral wire at the feeding end and
measure at the basement light switch, how many volts?
If I read that right, the neutral was also floating at the switch for
the dining room ceiling light. What is the source for the neutral at
that switch. The dining room ceiling light box is a prime suspect.
(If there are 3 wires from DR ceiling light to switch, the hot and
switched hot wires are required to light the ceiling light. If the
neutral is open to the switch, the ceiling light will still light. The
neutral is only used, along with the hot, for the circuit down stream -
which is your dead switch.)
One of the more useful tools can be a light bulb in a socket with
pigtail leads - probe hot and neutral wires and see if the bulb lights.
It will not show the 'phantom' voltage. But it sounds like you are doing
OK with your meter.
Do you mean you have two cables entering the junction box?
Normally a light switch has two black wires connected to it. One black is
the live wire from panel/upstream, the other black goes to the light.
Neutral is already connected and not switched.
In anycase, since you already identify it as an open neutral, it seems the
next step is to find where the opening is. If it's not in the junction box
you're working on, then it must be in the one upstream.
BTW, if the feeding circuit has no ground wire, where is the ground wire on
the 3-conductor cable connected to?
This look like a typical 2-switch with traveler, power through the
fixture. The fixtures are loaded into neutral in parallel. So when
you hook up the meter between hot and neutral, it ends up in series with
the fixtures, hence partial voltage. I am fairly sure that if you
simply short the neutral to hot, the lights will go on.
Now, the traveler part. That's the 3-conductor. Standard hookup
would be white to white, black (hot) to switch input, and traveler's
red and black to switch outputs (yeah, that would be a double pole
switch). On the other end of that wire would be another switch box,
also with a double pole switch, white on input, red/black on outputs,
allowing the lights to turn on/off by flipping either switch.
Now, you are saying, the box presently houses a single-pole switch, but
incoming wires are a 2 and a 3. How is it wired? I assume white to
white, but by any chance is it black to black through switch and red
capped? If that's the case, look for the other end of this wire.
There should be another switch there and that switch will likely be
switched to red.
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