Low Voltage on Neutral Conductor

[kmans999]

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).

[Tony Hwang]

Hi, Sounds like neutral wire lost continuity partial of full.

[peter]

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?

[kmans999]

[kmans999]

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?

[Bud--]

I agree.

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 weren't any.)

Good troubleshooting so far.

bud--

[scorrpio]

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.

[pipedown]

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 front.

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.

[Tony Hwang]

Hi, This kind of trouble shooting I always use low input impedance analog meter. Such as old work horse Simpson 260. On digital works I use Fluke and o'scope. Tony

[kmans999]

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.

Ken

[peter]

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 accurate summary?

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?

[Bud--]

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.

bud--