strange voltage reading on residential switch

[Riograndeelectric]

had a service call today in which customer said the TV went out and the outlets in the room with the TV went out and customer heard and saw flash.
customer did some trouble shooting on his owner before calling me customer has experience in electronics hence his reason for minor trouble shooting. he stopped at taking switches and outlets out and checking connection and voltage. customer told me he read 50-75 volts with with digital meter on a switch controlled wall outlet with the switch in the off position. I found that the neutral conductor on the hone run at the panel had become extremely hot and insulation melted along with the conductor itself.
I fixed the melted neutral although not sure why it melted the termination was tight.the 2 neutral wire below this one were also showing signs of overheating and melting insulation. all other on the same neutral bar did not show any signs on discoloration or melting.
upon fixing the neutral I was checking voltage and read 50-75 volts on the switched outlet with the switch in the off position with the switch on i read 120 volts.
I though maybe there was a neutral crossed in a another circuit. the circuit in question is a 2 wire circuit, house was built 1972 and has aluminum wire.
disconnected the neutral at the panel and rung it out to the neutral bar. I had no continuity/ Read open circuit which leads me to believe the neutral is not crossed with another neutral. why would I be Reading 50-75 volts between hot and neutral on a outlet with the switch in the off position.?

 

[Dennis Alwon]

Is the switch fried perhaps and leaking voltage?

BTW, try using spaces, punctuations etc when you post. It is very difficult to read

Had a service call today in which customer said the TV went out and the outlets in the room with the TV went out. Customer heard and saw a flash.

Customer did some trouble shooting on his owner before calling me.

Customer has experience in electronics hence his reason for minor trouble shooting. He stopped at taking switches and outlets out and checking connection and voltage.

Customer told me he read 50-75 volts with with digital meter on a switch controlled wall outlet with the switch in the off position. I found that the neutral conductor on the home run at the panel had become extremely hot and insulation melted along with the conductor itself.

I fixed the melted neutral although not sure why it melted the termination was tight. The 2 neutral wire below this one were also showing signs of overheating and melting insulation. All other on the same neutral bar did not show any signs on discoloration or melting.

Upon fixing the neutral I was checking voltage and read 50-75 volts on the switched outlet with the switch in the off position with the switch on I read 120 volts. I though maybe there was a neutral crossed in a another circuit. the circuit in question is a 2 wire circuit, house was built 1972 and has aluminum wire.

Disconnected the neutral at the panel and rung it out to the neutral bar. I had no continuity/ Read open circuit which leads me to believe the neutral is not crossed with another neutral. Why would I be Reading 50-75 volts between hot and neutral on a outlet with the switch in the off position.?

 

[SG-1]

I would have a concern that the breaker on that circuit may not be able to trip. If he heard & saw a flash a breaker should have been tripped.

Quite old they are.

 

[kwired]

why would I be Reading 50-75 volts between hot and neutral on a outlet with the switch in the off position.?

Switch possibly opens the neutral instead of the hot conductor.

Use a low impedance meter or put a load on the receptacle when measuring and the 50-75 volts will drop to almost nothing if that is the case. Measure to a known grounded reference and you will have 120 volts on the hot and nothing on the neutral unless there is a connected load then you will still have 120 volts to ground.


As for the overheated neutral in the panel - if aluminum conductor it does not matter if it was tight - it may have been loose at some time and has oxidized making a high resistance connection - it will heat up the higher it is loaded the hotter it will get which will result in more oxidation making the problem even worse.

 

[fireryan]

Ive seen cooper terminations on a neutral that are melted but everything seems to be tight. Whats the cause of that?

 

[jcole]

Leads me to believe there is a loose connection somewhere and the conductor is getting hot due to arching.

Is there a chance the circuit is getting overloaded?

I seen romex cable get hot because a staple was to tight supporting it.

Can u install an afci to see if it trips?

 

[Riograndeelectric]

Switch possibly opens the neutral instead of the hot conductor.

not 100% for sure but I did ring out the Romex going from the switch to the recp and verified the neutral and hot are correct and the recp. . there is only 1 Romex cable to the recp . switches are new replaced them when I was trouble shooting.maybe I should run an extension cord from another circuit and check neutral to neutral?

 

[bth0mas20]

read across the switch with an ohm meter and verify it closes and opens completly. It sounds to me like a bad switch.

If your reading voltage on the neutral it also could be an "open neutral" somewhere. Ive seen this before where the voltage to an incandescent bulb feeds thru and gives a voltage reading on neutral becuase its open somewhere in the circuit.

 

[LarryFine]

why would I be Reading 50-75 volts between hot and neutral on a outlet with the switch in the off position.?

Because you're using a voltmeter, which (usually) has a high input impedance, so it won't "load down" a sensitive circuit. It's doing exactly what it's designed to do, and it's accurately reading the voltage on that wire.

If you plugged the light in (making sure it's on) when you did that voltage test, you'd read zero volts. Think about the wire between the load terminal on the switch and the empty receptacle: It's an isolated wire.

It's just an unterminated wire in a cable with voltage being induced on it from surrounding wires, especially in a cable with a grounded conductor and an energized conductor. It floats somwhere between 0v and 120v.

For these reasons, I prefer a solenoid-type tester (aka a 'wiggy'). The low impedance prevents these readings, the hum is quicker than reading a meter, and we're testing for presence of power, not the exact voltage.

 

[Steviechia2]

Sounds to me like an open neutral. Is there any other plugs where this is happening or is it only this one switched plug? How about the other plugs on this circuit?

 

[bth0mas20]

check the neutral jumper installed by the factory on the outlets. I found one broken/burnt open on the first outlet in the circuit before.

 

[Riograndeelectric]

went back to day and disconnected entire circuit at the first device on the circuit I read 120V hot-neutral-ground on the same hot reading to the neutral and ground going to the next device I read 93 volts Hot-ground and 53V hot-Neutral.


I double checked these reading with my fluke 87 and my analog meter. I read same voltages on both meters my wiggly does not show any power between any wires. I am thinking that there is a neutral and or ground tied in with another circuit or neutral or ground are some how pinched in the wall or some how some where are some how letting some current leakage.

I ohmed out the circuit and it reads clear.

 

[Article 90.1]

All of the advice given has been great, but we still need to find out where the flash came from, and what caused it. Keep digging!

 

[LarryFine]

All of the advice given has been great, but we still need to find out where the flash came from, and what caused it.

Paparazzi?

 

[wptski]

went back to day and disconnected entire circuit at the first device on the circuit I read 120V hot-neutral-ground on the same hot reading to the neutral and ground going to the next device I read 93 volts Hot-ground and 53V hot-Neutral.


I double checked these reading with my fluke 87 and my analog meter. I read same voltages on both meters my wiggly does not show any power between any wires. I am thinking that there is a neutral and or ground tied in with another circuit or neutral or ground are some how pinched in the wall or some how some where are some how letting some current leakage.

I ohmed out the circuit and it reads clear.

As long as your Wiggy isn't defective, that sounds like "ghost" voltage but I've never read a post here where "ghost" voltage was a high as 120V!

 

[hurk27]

went back to day and disconnected entire circuit at the first device on the circuit I read 120V hot-neutral-ground on the same hot reading to the neutral and ground going to the next device I read 93 volts Hot-ground and 53V hot-Neutral.


I double checked these reading with my fluke 87 and my analog meter. I read same voltages on both meters my wiggly does not show any power between any wires. I am thinking that there is a neutral and or ground tied in with another circuit or neutral or ground are some how pinched in the wall or some how some where are some how letting some current leakage.

I ohmed out the circuit and it reads clear.

Things to check:

the strange voltages was answered in post 9

using an extension cord plugged into a known good receptacle on the same phase/leg

use a wiggy type meter to measure the voltage between each terminal and the circuit in question, to see which conductor/s is missing.

after finding the bad connection and repairing, check these things to see why it happened:

check wire size and ratting of breaker, #12 aluminum has only a 15 amp rating, #10 is only rated for 20 amps.

if the circuits are part of a multi wire circuit, make sure both ungrounded conductors are on opposite phase/legs in the panel, this can cause double the amps on the neutral if they are on the same phase/leg
check to see if the receptacles are stabbed in the back, this was never allowed for aluminum wire. a 3-light tester will show an open neutral sometimes as a reversed polarity when there is still a load on the circuit, if you don't have a loaded meter, then make a load with a pigtailed light socket with a 100 watt bulb in it, and place it across the meter your using to measure with, odds are if you didn't fix the circuit when you tightened the neutral in the panel you have lost the connection at one of the receptacles or light fixtures, using a plug in 3-light tester, try going through all the receptacles on this circuit, even ones that work, and plug in the 3-light tester and wiggle the receptacle back and forth, have a lamp plugged in and turned on so if you hit the bad receptacle it will let you know, other then that its a remove and look type of job till you find the open conductor/connection.

 

[Riograndeelectric]

thanks for all of the great device.

1 question is why am I reading 90 volts on my digital and analog meter's from the hot wire of home run to the ground wire going to the next recp and reading 50 volts from the home run hot to the neutral going to the next recp.
I am testing with all wires/ devices disconnected on entire circuit.

 

[LarryFine]

1 question is why am I reading 90 volts on my digital and analog meter's from the hot wire of home run to the ground wire going to the next recp and reading 50 volts from the home run hot to the neutral going to the next recp.
I am testing with all wires/ devices disconnected on entire circuit.

the strange voltages was answered in post 9

If you still need a demonstration, wire a 120v bulb of any wattage in parallel with the voltmeter's input, and test again.

A socket you can clip onto the meter's probes will suffice. Watch the meter while you connect and disconnect the bulb.

Only the readings with the bulb have any real meaning. The rest merely shows your meter has a high input impedance.

Testing for presence of real power and for the exact voltage call for different instruments. We recommend the solenoid.

 

[wptski]

Testing for presence of real power and for the exact voltage call for different instruments. We recommend the solenoid.

A DMM with a low impedance function or other low impedance testers on the market would work also.