Wire Reverse between Life and Neutral

  1. Hi,
    I really want to know if there is a way to do detection whenever wire been reversed between Life and Neutral. Any opinion guys?:smile:
     
  2. jcsd
  3. chroot

    chroot 10,427
    Staff Emeritus
    Science Advisor
    Gold Member

    Neutral and ground, when properly wired, have zero potential between them.

    - Warren
     
  4. Danger

    Danger 9,879
    Gold Member

    Love your username, dude... although it would seem to perpetuate the science-geek stereotype. :biggrin:
    If you have access to the connection points, you can just go by colour. (Here in Canukville, at least, the rule is black-gold/white-silver. White is system neutral, and black is hot.) If you have a black wire going to a silver terminal, somebody screwed up. Never take that as a given, though, because someone could also mess up the polarity of a plug if it wasn't part of the original wire (as in a lamp cord). Such things should always be checked with a meter. As Chroot said, if you show a potential between white and green (ground), it ain't proper.
     
  5. NoTime

    NoTime 1,570
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    Homework Helper

    There is a test plug that inserted into an outlet will show if its wired correctly.
    You should be able to find one in a hardware store.
    The cost is low, a few dollars.
     
  6. Danger

    Danger 9,879
    Gold Member

    Quite right, but it might not always be practical to use it in some applications, such as a questionable appliance. While I have no trouble hooking something like that into something like a vacuum cleaner with jumpers, we can't assume that the OP can do so. For household wiring, your answer is absolutely correct. For things plugged into that wiring, however, a different approach might be necessary.
     
  7. NoTime

    NoTime 1,570
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    One step at a time :smile:
    Given the number of houses I have seen that have incorrectly wired outlets, its probably something worth checking.
     
  8. Danger

    Danger 9,879
    Gold Member

    Hmmm... I hadn't thought of that. Up here, household wiring, during the construction phase, has to be done by a qualified electrician or someone under the direct supervision of one. You would only encounter a faulty installation in the extremely rare case of a householder with no electrical knowledge replacing or installing an outlet on his own. Good point, though, especially if the OP is someplace with a lax construction code.
     
  9. This method works, but I do not advise anybody to try it unless they are sure that they have a consumer unit that can cope with this. This is not as far as I know industry prcatice but something I have taught my self by experience sorting out 100 years of bodged Gas, Electric and water in my home.

    This assumes that you are starting with a consumer unit with an Earth Leakage circuit breaker (ELCB) each ring has either a fuse or an Residual Current Device (RCD)/ Residual Current Circuit Breaker with Overcurrent Protection (RCBO) on the Live wire. (This is UK by the way, I assume its the same where you live, hence don't try unless your sure).

    On the ring that has the suspect wiring, pull the ring Fuse/RCD/RCBO to isolate the ring.
    Now connect the Earth and Live together - Nothing will happen
    Now Connect the Earth and Neutral together - The ELCB will trip due I believe to the small current imbalance on the Neutral Star Point at the local substation.

    If the above happens you are wired correctly.
    If the reverse happens your Luive and Neutral is crossed
    If nothing happens your Earth connection/ELCB is faulty.
    If you get electrocuted your rings are cross wired.

    P.S. Check that the circuit is dead or ask ask your partner to stand nearbly with a broom to poke you off if you think you may have cross wired ring mains.
    I had a power ring in one room that came from a spur on the lighting ring for the floor below.
     
  10. It does not matter in most cases if they are reversed on an AC system. The neutral in the US is grounded to facilitate the overcurrent protective devices, ie breakers. Some newer consumer devices have only 2 prongs on the power cord. These devices require the outlet to be wired correctly in order to have the protection of the circuit breaker. To answer your question all newer outlets have one slot in the outlet larger than the other. If you stick the probes from a meter, one into the larger slot and one into the ground hole and get a potential voltage the outlet is wired backwards. The larger slot is supose to be the neutral, and therefore should be no potential between them. And Danger was right about the color of the terminal screws. Gold for hot, silver for neutral and green for ground.
     
  11. turbo

    turbo 7,366
    Gold Member

    For sure, spring a couple of bucks for a tester. I used to play guitar and sing in blues/rock bands and I got "bit" by my mic a few times until I smartened up and started checking the wiring of every outlet on every stage before performing. It seems that a lot of these old joints were wired by amateurs. Lots of the old Fender amps were made back before polarized, grounded outlets were common, so I either re-wired mine to conform to modern standards, or at least taped a little diagram with a short l and a long l to the plug to indicate how it needed to be plugged in. Actually, I ended up converting all but one amp eventually. There's a little gem of a blackface '65 VibroChamp that I want to leave as original as can be.
     
  12. Please don't post things like this. It is totally wrong. If too much current flows in the 'hot' wire no matter what the return path is the breaker will trip.
     
  13. Do not ask this guy to work on your wiring.

    Ground/Earth is NOT the same as AC Neutral.

    There is always current flowing on your single phase Neutral, Unless you have 3 phase power the Neutral cannot be connected to Earth, and even in 3 phase only at a well balanced star point.

    The reason why so many appliances have no Earth is because they are double insulated so it is theoretically impossible for AC current to be present on any external surface.
     
  14. turbo

    turbo 7,366
    Gold Member

    Clean-up in aisle 3. Go look at the 220V entrance in your house (assuming that you are on a US-type entrance). Neutral is tied to ground. You should see no potential between neutral and ground at any outlet. In fact, if the neutral-to-ground connection at your entrance box is poor, when a big load comes on-line on one leg of your entrance, it will shift the potential of the neutral, lowering voltages on that leg, and raising the voltages on the other leg. This is a potentially dangerous condition. Neutral must be tied to ground.
     
    Last edited: Nov 24, 2006
  15. Ummm, yet another correction. Neutral MUST BE TIED TO THE CENTER TAP ON THE TRANSFORMER. If the neutral to transformer conntection is poor it will shift the voltage like turbo described. I prefer to say ground is bonded to neutral and not neutral is bonded to ground. Yeah, I'm being nitpicky but it implys that the neutral is the conductor instead of the ground being the conductor. A poor connection between neutral and the ground rod or water pipe has nothing to do with voltages shifting.
     
  16. turbo

    turbo 7,366
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    Actually neutral IS the center-tapped lead from the transformer's secondary coil and the two 120V AC legs are the hot lines from the end taps of the secondary. If the neutral line is not firmly tied to ground at the entrance panel, large loads on either leg will cause voltage shifts. This happened in my old house a couple of years back. Linemen from the power company came to check the transformer at my request, then told me that the transformer was fine and that problem was probably a bad ground to neutral connection in my entrance panel. It was. 1/4 turn with a screwdriver cleared it right up.
     
  17. Yes, this is basically what I said in my last post.


    No, no, no, and.................................. NO! It has nothing to do with connection to what I call ground. If the neutral busbar where all the white wires attach to in your service panel has good continuity all the way back to the transformer then you can completely remove any grounding to ground rods and water pipes and your voltages will stay balanced. This is how mobile homes are wired. They have a neutral bus bar that is isolated from the ground bus in the service entrance panel. However, outside where the mobile home plugs into the ground and neutral will be tied together. Once again, you can defeat this ground connection and as long as the neutral is not disturbed and voltages will stay balanced. Ground is not meant to carry current except during a fault.


    I don't doubt that a loose screw in the neutral conductor at your service panel would cause a voltage shift, but it has nothing to do with being bonded to what is correctly referred to as ground. I also don't doubt that this is what they told you.
     
  18. turbo

    turbo 7,366
    Gold Member

    Well, that was the screw that I tightened - the clamp on the neutral block that clamps the ground wire. The problem stopped instantly.
     
  19. What are you calling the ground wire? I'll post more later.
     
  20. turbo

    turbo 7,366
    Gold Member

    It is the clamp on the neutral block that clamps the ground wire - the multi-stranded lead that connects the neutral to the ground on cold-water entrance line that feeds the house. The voltage excursions dropped from +- 10-15V per leg (opposing depending on which leg your were monitoring) to negligible. I restore tube amplifiers as a hobby and once pursued it as a business, so I'm not entirely unfamiliar with these concepts.
     
  21. Well that's a pretty scary installation Turbo. The wire that connects the neutral to the water line is never supposed to have any current flowing on it except in certain fault conditions. Since you were having voltage fluctuations when certain appliance turned on and off and fixing that connection got rid of those fluctuations tells me you had current flowing in that wire AND the water pipe that was normal load current. This also tells me that the main neutral that goes between the service panel and the transformer was weak. I'll post more in a while.
     
    Last edited: Nov 24, 2006
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