I was called this a.m. to see if i could diagnose an electrical problem at the rental prop of a current customer
A junction box started sparking and smoking till they turned off the breaker… I thought the prob was a loose wire nut allowing a hot to contact the neutral..
I put everything back in place now half the outlets have 120V the other half have anywhere from 40 to 70V What the heck?
any help is appreciated
Replies
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Everyone in the peanut gallery repeat after me.
PHANTOM VOLTAGE.
Putting on my Karnack hat I see that you have a Digitial voltmeter and that one of the wires is open. And you are measuring capacitive coupling between the the wires and other hot wires.
Iv you measure anything more than 5 volts or less than 100 then it is phantom voltage.
Notes, that there are a few other conditions that might cause strange readings such as lighted switches, but the circuit would still work.
You did not indicate between what wires you made the measurements. Try hot/neutral, hot/ground and neutral/ground.
That will point ount the open wire.
recheck the connection, then check futher back in the box, then checkat the panel.
If none of those places then it is either in the cable, itself or in another box.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Phantom voltage
was I tooo late
Ductape can fix EVERYTHING!!!
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https://www.nema.org/prod/wire/build/upload/Bulletin%2088%202003.doc
"Care must be taken to be sure that the voltage reading is a phantom voltage, which is caused by improper use of high impedance multimeters, and not as a result of a cable defect or improper installation, which may result in a shock hazard.
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"In order to help minimize the likelihood of reaching a wrong conclusion from this phenomenon, NEMA recommends the use of a UL Listed or OSHA-approved low impedance multimeter in place of a high impedance multimeter or other high impedance measuring device for testing on open conductors where there is no hard electrical connection. Without a low impedance measuring device, a high voltage reading is an inconclusive indication of possible faults in the cable."
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Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 2/14/2008 5:57 pm ET by Riversong
Good job, Andy ! ! Guys, I think we have another Piffin in training here !
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Greg
here is a "famous" entry at Wikipedia re: Phantom Voltage.
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Thanks for all of your replies
I am still puzzled as to :
1 The collection of wires sticking out of the junction box was sparking and smoking yet, according to the mechanics that owns the business, did not trip the breaker
2 Why half the outlets in his place have 120V reading and the other half have a variety of much less all off of the same breaker and all fed from this same junction box
Weird Weird Weird
This place is a code violation farm, I was asked to see if I could quick get them back up and running.I don't think so.
Thanks for all of your help
"1 The collection of wires sticking out of the junction box was sparking and smoking yet, according to the mechanics that owns the business, did not trip the breaker"Very "normal".Assuming that the breaker was functioning and of the right size then it takes current over the rating to trip the breaker.But if you have a poor connection than and current withing the rating of the breaker being drawn you will get lots of heat generated at the bad connection..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I wrote this in response to a similar question a few weeks ago, some outlets were reading 115 others 80. had a client that had a similar problem the lights in the house started dimming first just a little then a lot. Told him to call the power company when it was slight they monitored it for a week and said not a supply problem then it started getting worse. That is when I referred him to my electrician. He did some readings was getting 115 on one side 80 on the other.Turned out that one of the main lugs above the main breaker had corroded so bad it was almost floating free. It was not the set screw for the 0 wire it was the lug to rail connection.This panel was only about 8 years old it was an exterior panel with meter base on one side main breaker on the other with about 20 breaker slots. I think a combo panel.So it could be something like that even a lug on the meter base, connection at the main the lug on the rail. DO NOT MESS WITH ANY THING ON THE SUPPLY SIDE OF THE MAIN BREAKER UNLESS Qualified IT IS LIVE! As explained to me by my electrician one side is under worked the other overwork could be a potential fire risk. If you feel qualified take a reading of both sides, not at an outlet but at the breaker. beyond that I would refer him to an electrician.Wallyo
very good suggestions !checking the bus voltage is a given for those of us that play with Electricity every day
but some folks mis-interpret the readings and should know when to quitI would only add that since the breaker never tripped,
and just to err on the side of caution , change the breaker ...
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The problem in that house was a progressive one, it was hardly noticeable at first and got worse and worse. I would have to check with the owner but the tip off was she plugged something in in the office sparks flew out the outlet left a burnt singe on the outlet but I don't think the breaker popped either. That was the weird part I looked at it got the different readings at the bus called the electrician.Wallyo
circuit breakers should be exercised regularly. just like GFIs and the best way is without a load on itbut that is something that is just not done in most homes, or even commercial installations.the assumption is the thing will work when it's supposed to, even years laterout of sight = out of mind.
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When you say exericised do you mean turn off and on every now and then?Wallyo
yes..on / off several times.........
and best if done with NO Load because it's always been a leap of faith to expect them to work 100% of the time, unlike fuses.
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Thanks for your suggestion I think the problem here is that things are so screwed up and rigged to work that nothing is as it seems in a logical wiring setup.I have a question about what would give a normal reading of 115V on some and a lower reading on others were they on separate legs? In this case the outlets are all on one breaker.I have already bailed on this one . I think something is fried down the line in this place and causing voltage to bleed back through the hot or neutral, just a reduced amount.A big problem is that if there is a burnt outlet/switch/junction box
it will be black..... this is a back alley auto garage....EVERYTHING is black in there.
Your theory sounds right if all on one breaker I would guess something between the two outlets the one 115 and one at 70 is burnt out your are getting half or the 60 cycles because it is only one side. Time for them to spend the bucks.Wallyo
"Your theory sounds right if all on one breaker I would guess something between the two outlets the one 115 and one at 70 is burnt out your are getting half or the 60 cycles because it is only one side."Please, for your safety and everyone around you, start far away from any thing electrical.THE PROBLEM IS NOT BECAUSE OF "HALF CYCLES"..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill
My or was meant to be an ofOwmythumb was Indicating that the problem is occurring on one breaker, Half are reading 110 the other half 70 it sound like a neutral or hot has been lost between the one reading 115 and 70 and the people he is trying to help are at the point that it is "Time for them to spend the bucks"by that I was implying they need to hire an electrician. I should of been clearer.Wallyo
this is a back alley auto garage....
Your said junction box in your first post. Is this a conduite job?
I know you have already bailed on this, but for us cyber space electricians could you tell us more?
It may be something as simple as a skinned wire in a conduite run.
More info?Sure, here is the nightmare scenariomost of the building is conduit...this particular junction box has the feed for the outlets and switches and also contains the return feed after the switches to branch out to the lightingIt also has no cover on he box since it would be hard to smash all 25 or thirty individual wires into a single box ...apparently since there was no cover someone thought it would then be ok to tap into here with two romex lines for a new outlet and light in the garage officeAND at some point in time they also added a double outlet box next to the switches by the front door....then they realized that they didnt have any neutral in that box just constant hot in and switched hot out.The bright idea for this dilemma was to run a single wire (one white pulled out of romex) from the outlets to the junction box.Thats only what I can visually see , oh ,they also have an outlet on the back wall fed with an old extension cord, I guess they ran out of Romex?My first thought was "no, no, no, no, no ,no"
My second thought was "RUN BOY RUN!"
I'd go second and run run run! As a handy man the liablity is way to much.
With all that hay wired stuff in there you were right tbail out. the last guy to touch it is the one the insurance company will be looking for when the place goes up in smoke.
Since half the outlets on that one breaker are showing the correct voltage and the other half is low, I'll stick with my original diagnoises. They have a intermittent short from a hot wire in the conduit feeding the low voltage outlets. It is likely just a skinned spot on the hot leg of the bad half of the circuit. Somewhere in that j-box is a homerun to the breaker box. The good half of the circuit and the bad half are tied to it.
Once that bad wire is located, a pull in/pull out to replace the bad wire would fix the problem. But like you, I wouldn't touch it, short of a total rewire with permits and all.
A short would trip the breaker or start a fire. There's simply a bad connection somewhere. But it sounds like there is a lot wrong with the workmanship and practices.
Mark, I did not say a dead short, but even they will not always trip a breaker or start a fire in a conduit install.
Trust me on this one. I have seen 277v deliberatly shorted to conduit and all it didd was rattle the pipe. Same thing with 120v. The load has to go over current protection rating of the breaker for it to trip. Lose of continuity in the conduit connections can also mean a weak path to ground and the circuit won't go over current.
A simple skinned spot on pulled in wire is enough to cause a weak short to the pipe and you get a voltage drop in the circuit. I've had to trouble shoot many of them over the past 24 years.
Dave if they only have 70 volts on one part of the circuit and it is caused by a high resistance series then there would have to be some kind of load on it.In most cass with that load of voltage most loads would not be functional on they would be removed or turned off.So it would have to something that is small and alway on. A transformer or a small light someplace.But without any more detailed knowledge I still say that the evidence best indicates a open and he is measuring phantom voltage..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
You are quite possibly correct, but we just did a pull out/pull in for a skinned wire. The wire was skinned about 8" down from a pulling C. Not a big honkin removal of the jacket, but about a 4" thin spot and a 1/4" of bare conductor showing. The circuit read between 40 and 70 volts until we pulled on the wire. Then we could get 120v, but it would immediatly drop to the same low reading when we relaxed the tension.
Kind of falls in the strange but true catagory, but it is not the first time we have seen this kind of thing.
I,m not much of a theoretical electrician, so I base my trouble shooting on experience. My survival is based on a healthy respect for the voltages we work with and a knowledge that everyone that worked here for the last 100+ years thought they were electricians.
Sometimes it is downright scarey to think an electric utility is so haywired.