An electrical wiring puzzle

Discussion in 'Off Topic' started by r0k, Feb 15, 2010.

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  1. r0k

    r0k Dazed

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    Today in the BH break room, r0k offers some electrifying entertainment.:cool:

    I was working on some old house wiring and it was a real joke. I was going behind some rank amateurs. For one, they had connected two normal (SPST) switches in series where there really should have been two 3 way (SPDT) switches. :eek: Where there were supposed to be two traveler wires, there was only one. For the other traveler wire they stuck a wire nut on one end (at the top of the stairs) and tied the other end (at the bottom of the stairs) to what should have been a ground terminal. :eek:

    In another room they proceeded to do some mysterious stuff I couldn't decipher at first. :confused: Look at the clues and think about the diagnosis before you scroll down to see my solution.

    In the US, we use a 110v system with Hot, Neutral and Ground. Typical homes are 220v with two phases of 110v and a Neutral between them. Neutral is connected to earth ground (by driving a 48 inch copper stake in the ground) at the panel coming in the home and "on the pole" just below the step down transformer that makes 220v from 4800v or whatever is on the highest wires. It turns out that common soil is an excellent conductor at 60hz which is why we call it "earth ground". We have wires coming from the power plant but if one of the hot lines touches the ground, it is like a huge dead short and should blow a breaker upstream.

    There are $5 testers available to find ground faults in house wiring. The testers have 3 lamps. The lamps are wired between the three terminals of a standard "type b" plug. For a correctly connected plug, the red lamp is off and the two yellow lamps are on.

    [​IMG]

    -Y- = open ground
    --Y = open neutral
    --- = open hot
    R-Y = hot ground reverse
    RY- = hot neutral reverse
    -YY = good

    Some testers have a GGCI "test button" which causes some current to flow from hot to ground and "should" trip a GFCI outlet.

    At this point, I should mention that I was seeing
    RYY = ??? All three lamps lit up
    If I plug in a 60 watt load it works fine and each receptacle seemed to be working except that the ground fault tester said "something was wrong"...
    If I push the GFCI test button, the two LED's would be lit showing the circuit was good. :confused: :eek:

    ... no cheating ...

    More data...

    I measured 52 volts from Hot to ground and I measured 70 volts from Neutral to ground.


    ... I mean it ...


    What was the matter with my wiring?
    Was it swapped wires?
    Was it an open?
    Was there a partial "resistive" short (hence the wierd voltages)?

    Having the red led lit began to convince me that I had a hot/ground or a hot/neutral swap and I was inclined to find the first plug in the string and swap the incoming lines. Before doing so, I decided to do a little more work.

    Give up? Click here...

    I checked the voltage between hot and a known good ground. It was 115 volts. What the heck? The red LED was on but hot and neutral were not reversed.

    Well, it turns out the designer of this tester neglected to list one case on his chart:

    RYY = -y- = open ground


    Since ground was floating, there was a path through two of the leds that could light them up dimly with the third LED on full brightness. Pushing the GFCI test button altered this path and caused the red LED to go back off.

    To test my theory, I went over to the hardware store and bought a 30 foot length of green insulated 14 guage solid wire and connected one end to a known good ground. The other end, I tapped on the suspect ground. I was a little worried that sparks would fly and current would flow. After all, I had measured the suspect ground at 70 volts from neutral, which is 70 volts from ground. Nothing happened. Now the tester shows -YY with the "jumper wire" connecting the "bad ground" to a "good ground". So now all I have to do is find the box there the doofus neglected to bring the ground up from the main breaker panel, or a ground wire broke, and repair the damage. Even if the problem is a broken ground wire "in the walls somewhere" all I have to do is run a separate ground conductor to one of the outlets. Problem solved!


    ... Drag here.
     
    Last edited by a moderator: May 18, 2015
  2. jigwashere

    jigwashere Mobile Deity

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    I seem to recall having a similar problem (this was about 15 years ago, so my memory is likely faulty). All the wiring checked out, but there was still some current on the ground. It turns out I had a UPS plugged in on that circuit and it was trickling a bit back through the ground.

    Again, my memory is very shaky on this. All I know is that once I unplugged the UPS, everything tested normal.
     
  3. hal

    hal itchy and cold feet hal

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    My friend, r0k, you're an electrics expert. Your teachers shall be proud of you. Actually, your true merit is not the diagnose, but reverting the stupid things done by a buncha rookies. Cause, as some hal you know once said, fools are very inventive.

    I did know that the common low-tension split in the US is 115V, and that it's common to saddle up to a 220V contract for households. One little detail: AFAIK, that GFI tester is only intended for single phase (or, am I wrong?), that's why I think the manufacturer didn't omit your option, cause it's not intended for two phases. It's just that if you use it in two phases circuits, actually your mentioned option is a must. Just like Jig, I recall some similar incident a bunch of years ago; I spent some three hours trying to figure out what was wrong and where. It wasn't me either. Some dumb@$$ had connected two phases WITHOUT a physical ground near the step down transformer (and with no local ground stake). The neutral they connected, which in the end is a distant ground, wasn't enough to offer an effective grounding and when somebody connected an electrical appliance intended for 3-phase, I had a readout of cycling meshes as if it really were a 3 phase coming in (...as I said, with only two phases). The problem was lousy grounding, but the effect was very real, until the 3-phase appliance whined for the lack of amperage.

    Those guys were lucky not to fry anything in the surroundings, themselves included. A single phase, wrongly spliced, can do a lot of damage.
     
  4. r0k

    r0k Dazed

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    Hal, I should clarify I was not ever testing more than one phase at a time. The first $5 tester I tried did not have a GFCI test button so it was always stuck with all 3 lights on. To find out what was inside these testers, I found a patent from 1976 (3984765) that included a schematic which confirmed my suspicion that they merely connect lamps from one leg to another. But it also added a wrinkle which was a switch with an extra resistor to leak current from hot to ground to force a working GFCI outlet to trip. I spent a little extra ($8) and got a tester that included the test button, hoping that all 3 lights would not turn on for an "open ground". They still turned on, but the GFCI test button connects essentially a resistor short across the red led so it would stay turn on for a true reverse fault with the GFCI test button pushed.

    [​IMG]

    the $5 tester had...
    NEUTRAL <-- led -- resistor --> GROUND
    GROUND <-- led -- resistor --> HOT
    HOT <-- led -- resistor --> NEUTRAL
    the $8 tester added...
    HOT <-- resistor -- momentary switch --> GROUND
    which is the same as fig 9 above. It is dangerous for the companies that sell these testers to omit the all 3 lights on option from their table. A person could assume that red on ALWAYS means hot and neutral are swapped and make things a LOT worse by swapping hot and neutral when they see all 3 leds on. The worst part is, after the misguided swap, all 3 leds would STILL be on. :eek:

    It turns out that if all 3 LEDs are on, and you can push the GFCI button to get the red one to go out, you have an open ground.
     
  5. WyreNut

    WyreNut Palm Aficionado

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    <A shudder runs down WyreNut's spine!>


    Hopefully you aren't reading any voltage from Neut to Ground now... They may not have bonded the Neut anywhere.

    Did you check to see if the ground connection was to a water pipe that had been "repaired"? (instead of a ground rod). I've seen folks dangerously replace a brass valve with PVC ones (or a PVC section of pipe) and if the water was shut off, they lost their main ground connection!

    WyreNut
     
  6. r0k

    r0k Dazed

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    Good point. The water is shut off. However, most of the building has a good solid ground and only this one circuit has a bad ground so I suspect a broken wire, most likely where the previous homeowner tried to make a repair and didn't notice they broke the ground wire coming from the panel. They even put in a gfci outlet on this leg in some misguided effort to solve this problem. I yanked out the unneeded gfci yesterday evening and later this week I plan to go by and plan to either locate the broken ground and repair it or run a separate ground wire so that there is a good ground for the devices on this particular breaker.
     
  7. DragonHunter

    DragonHunter Bow, bow, bow, bow

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    Fun stuff. I had some wiring adventures when I was doing some remodeling about 7 years ago. I remember having something funky as well along the line, but it is way to fuzzy to even try to remember for sure.

    I always enjoyed the electronics puzzles I came across....
     
  8. hal

    hal itchy and cold feet hal

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    Ah, OK. Pretty interesting.

    VERY good point. Saw it happen a couple of times.
     
  9. PDA Bach

    PDA Bach Dunsel

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    Even though this thread has gone to sleep, I spent part of a weekend running a ground wire to two outlets because a previous owner had simply cut it off. (!!!!!!!!!!!)

    I don't like fishing wires in finished walls in the first place and the fact that it was an interior wall did not assuage my temper at the supreme idiocy of their action.
     
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  10. r0k

    r0k Dazed

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    Ha ha! Funny you should mention that today! It has been about a month since I suffered through this idiocy but yesterday I was showing my brother-in-law around the basement and pointing out where I had to run the single conductor green insulated ground wires to replace those cut away by the clueless previous homeowner and we both laughed about it. Now I see that you had to deal with the same crap, PDAB. Amazing. I wonder what people think those bare conductors are for? And can't they use the internet and look up how to wire an outlet before they just go and cut them?
    [​IMG]
    Ok, I know these kind of bonehead moves are most often perpetrated by people who couldn't use the internet even if you showed them where the "any" key is. :D
     
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