Home wiring question

Discussion in 'General Electronics Chat' started by mbohuntr, Jun 5, 2011.

  1. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    New mystery!! Insulation breakdown or some sort of capacitance?

    I was replacing a perfectly normal ceiling fan with something my wife likes better when I came across this mystery. The fan itself is controlled by the fan switch, while the light can be switched with either the light switch, or a wall switch.
    I turned off the breaker, and removed the entire fixture. I then wanted to verify which hot was for the light, so I re-energised the breaker and put my meter on the bare wires in the ceiling. The black was 120v as expected, but when I checked the red to neutral I got 46v??? I checked the black to red and got around 65v???
    Thinking the switch might be bad, I removed the red and left both ends open. Then tested the switch. Nothing. I then energised the black, and tested to neutral. 120v. Red to neutral 46v?? (The red is disconnected at BOTH ends!!!) Then I went to the wall switch side and repeated the test and got 20v red to neutral??
    Then I set the meter for resistance and checked for continuity red to black, and neutral... none. Then I set it for AC current and got 20uA red to neutral. So there are NO physical connections!!! I Didn't think there could be inductance here with such low voltage?? What gives?? I disconnected the red and taped off the ends so I'm using only the black for both fan and light. Replacing the 14/3 is gonna be next to impossible since the basement is finished. I even thought about the neutral being hot until I got 65v red to black. Any thoughts???
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Over unity is not an allowed topic on AAC:p;):D:):rolleyes:

    Isn't red usually limited to 220V wiring? Was the original fan wired with the two switch configuration?

    Does the switch controlling the red wire also control something else that could be back feeding?

    When you get into something that YOU didn't originally wire in a house almost anything is possible. The older the house the more the possibilities:confused:
     
  3. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    The circuit is fed by a single 14/2. The black is pigtailed to the 14/3 fan black which is controlled by the built in pull chain, and the wall switch. The Fan red goes from the load side of the switch to the fan. I thought about backfeeding as well, so I isolated all wires including the neutral. Then powered only the circuit. The wires in the ceiling were all disconnected. The red should not be able to pick up any voltage since both ends were free, and black to red, and red to white were almost 120v when added??? I thought a nail might have partially went through the insulation, but there is no continuity???
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    So what was the red to earth voltage?

    Which is another way of asking what is your neutral to earth voltage?

    Seeing a substantial voltage on the neutral is not uncommon.
     
  5. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Red to neutral was 46v at the ceiling, and 20v at the wall switch end.
     
  6. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    I guess I don't understand how I get potential on a wire disconnected at both ends unless the insulation is bad???
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
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    If you are using a modern meter, probably rated at 1Megohm input, you are seeing the effects of capacitive coupling through your wiring. An old meter, like a Simpson 260 rated at 50 Kohm/volt, would not have that problem. Get yourself a pig-tail socket and a 7 watt light bulb to do your testing. Light on=power, Light Off=no power.
     
  8. #12

    Expert

    Nov 30, 2010
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    It's true. You must have some kind of load besides a volt meter. Today's meters are just too sensitive for house wiring. I have a 10 meg Fluke and the red lead reads 1.36 volts on the ground wire with the black lead not connected to anything! What I do is put alligator leads on my meter probes and put a resistor in parallel with them. Something like 1k for coin batteries, 68k-2 watt for house wiring. The light bulb works just fine. and ps, sometimes a red/black/white cable is used for a 3 way switch or a dual load like a ceiling fan.
     
  9. someonesdad

    Senior Member

    Jul 7, 2009
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    BillB3857 and #12 are right -- electricians sometimes call them "phantom" voltages and are usually from capacitive coupling over a decent length run of wire. It's why lower impedance testers like VOMs, light bulbs, or solenoid testers are sometimes an advantage. The cure, as mentioned, is to lower the input impedance with a resistor in parallel -- which is usually done with a suitable resistor (use V^2/R to make sure you have a resistor of sufficient power rating where V is the RMS line voltage).
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
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    This was not an answer to my question which was

    The emboldening was mine.

    Warning: Those who do not properly distinguish between line, netutral and earth often end up with serious accidents.
     
  11. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    I assumed that since (yes , I ASSUMED:() there was continuity from ground to neutral, and no voltage between the two, they could be treated as the same. Is this wrong? I even checked the panel box for a separate neutral buss from ground. (there is) The voltage was the same in any event. Red to neutral and red to ground. Are you thinking of a bad earth ground? There is a large (#4?) copper conductor from the box thru plastic conduit to the outside and into the ground. When I get time, I will re-open the circuit and check with an analog meter. Thank-you all!!!!
     
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
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    OK so you could follow others' advice and see what happens if you try to draw some current from your 60-odd volts through a resistor connected between red and neutral or earth.

    I expect it is capacitive pickup that goes away when you try to draw current.

    go well
     
  13. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I'm going with this guy's questioning. Further, I'd be asking what are the voltages of red, black, and neutral to ground. Sounds like a 3 way switch arrangement, no big deal. The query is, is the white a neutral or is it the identified wire. If it's the identified wire, it should have no voltage (or very little) to your box bonding. If it's a neutral, it may have the imbalanced currents voltage riding on it.

    In industrial work, after locking out, I measure for any voltage to ground before engaging a circuit. With most lines parallelling for possibly long distances, I may see a small voltage initially, but that will drain quickly with my fluke meters.
     
    Last edited: Jun 5, 2011
  14. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Thanks for the help guys!! Definately not a three way arrangement. The 14/2 feed goes into a 14/3 and the red traveler is powered thru the wall switch. Should have been straight foward! I took the liberty of drawing it w/ Multisim. What a PITA! @ Studiot... Since I will eventually be going into industrial electrical, What is the purpose of checking neutral to ground potential? A bad earth ground?
     
  15. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    How does this fit in?
     
  16. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    There is a second switch in series controlling the light that wasn't part of the circuit issue because it was always left closed.
     
  17. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    then it's not 'either', which would have indicated a 3 way. Did you measure your wires to box bonding?

    Your situation could of course be a number of things, but lets discuss a bit about the 'neutral'. It's kind of like the 'ground' thing that is a misnomer. 'Neutrals' only exist in a circuit that has at least 3 wires, two or more phases and a return. The neutral carries the imbalance between the two phase loads, maintainig a 'balanced' voltage potential. The 'identified' wire carries all of the load current, all of the time. The two by code are colored white and have a common connection point. They mean two different things however.

    If you have two balanced and connected loads between two phases, the current runs through them. If you take the common connection back to mid connection of the supply, as in a 'neutral', no current will flow through it, but maintain it's flow through the balanced loads. Upset that balance, and current now begins to flow through the neutral.

    The 'identified' wire is the return to the common connection from a single phase. What ever current is allowed to flow from the hot phase, flows through the return.

    If one decided to tap off the first examples 'neutral', an 'identified' wire for a seperately supplied circuit, what happens. Well, as long as the load on the first circuit is balanced, then the neutral will return what ever the 'identified' wire is supplying it. If the loads in the first circuit become unbalanced (which is almost always the case), the 'neutral', will now carry what the 'identified' supplies as well as the imbalance. This additional current flow can show up as imbalanced voltages. Larger voltage rises are typically matched by poor connections along the line.
     
  18. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Yes I wondered if your neutral was not properly earthed.

    I also wonder about the + & - symbols on the ac source in your diagram?

    It is also a little difficult for me because US and UK regulations are quite different.

    In the US (so I understand) it is a legal requirement for the consumer to earth the neutral at the supply box/transformer (and nowhere else).

    In the UK it is illegal for the consumer to earth the neutral anywhere.
     
  19. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Oh, I think I see where your coming from. Here in the U.S., Residential wiring is almost always single phase 220v. Are you thinking of a three phase wye type imbalanced load that makes the neutral current rise? Yes, I checked the neutral bonding at the box, it was good.
     
  20. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Sorry about the schematic, Multisim is pretty good for electronics, but lousy for residential wiring. I used a single phase AC supply to imitate the panel box in the basement. (not 100% sure here), For residential service, our poles drop a single phase into a transformer and step it down to 220v. Then (I think) that secondary is a split phase that carries two 110v lines into the home. It is two conductors wrapped by a ground. At the panel box, each conductor goes into a leg of the box, and the ground goes to a buss that is bonded to the box frame, and another ground comes from there to the outside and into a 8' ground rod. All the neutrals in the home are brought back to the box and into a separate buss that is mechanically bonded to the ground buss.
     
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