Wire Reverse between Life and Neutral

  • #1

Main Question or Discussion Point

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:
 

Answers and Replies

  • #2
chroot
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Neutral and ground, when properly wired, have zero potential between them.

- Warren
 
  • #3
Danger
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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.
 
  • #4
NoTime
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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.
 
  • #5
Danger
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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.
 
  • #6
NoTime
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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.
 
  • #7
Danger
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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.
 
  • #8
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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.
 
  • #9
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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.
 
  • #10
turbo
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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.
 
  • #11
Averagesupernova
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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.
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.
 
  • #12
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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.
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.
 
  • #13
turbo
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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.
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.
 
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  • #14
Averagesupernova
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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.
 
  • #15
turbo
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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.
 
  • #16
Averagesupernova
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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.
Yes, this is basically what I said in my last post.


If the neutral line is not firmly tied to ground at the entrance panel, large loads on either leg will cause voltage shifts.
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.

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.

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.
 
  • #17
turbo
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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.
Well, that was the screw that I tightened - the clamp on the neutral block that clamps the ground wire. The problem stopped instantly.
 
  • #18
Averagesupernova
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Well, that was the screw that I tightened - the clamp on the neutral block that clamps the ground wire. The problem stopped instantly.
What are you calling the ground wire? I'll post more later.
 
  • #19
turbo
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What are you calling the ground wire? I'll post more later.
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.
 
  • #20
Averagesupernova
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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.
 
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  • #21
Averagesupernova
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The below link is a pic of the top end of my 200 amp service. Pretty basic stuff. The three large wires are from left to right: Hot, Neutral (white tape), Hot. The smaller white wire that loops up and goes off to the right is a neutral that feeds a 125 amp subpanel.


http://i137.photobucket.com/albums/q206/catchmedavid/100_0444.jpg" [Broken]




This next link is the neutral busbar on the right side of the panel. Notice the large green wire attached to it some past half way down. This feeds the subpanel and is a ground so no current should EVER flow in it except in a fault. Once past the main service, neutral and ground cannot share the same wire as it does from the transformer. The large bare wire above it is a ground wire that goes to a water pipe as it comes through the concrete block wall. Same thing here, no current should ever flow through it except during a fault. Turbo, am I to understand that this large bare wire above the large green one would be the equivelant to the one that you tightened in your service panel that straightened out your voltage fluctuations?


http://i137.photobucket.com/albums/q206/catchmedavid/100_0445.jpg" [Broken]
 
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  • #22
Averagesupernova, I noticed your power supply wires are Aluminum? What's the Code in your country?
 
  • #23
turbo
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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.
I have a feeling that the ground reference at the transformer was not that great. The soil in that location was well-drained sand, so a rod-type ground might not be the best choice. Once the neutral had a good reference to my cold water main, the problems went away.
 
  • #24
Averagesupernova
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I have a feeling that the ground reference at the transformer was not that great. The soil in that location was well-drained sand, so a rod-type ground might not be the best choice. Once the neutral had a good reference to my cold water main, the problems went away.
Once again, the ground rod at the transformer should have nothing to do with normal load current. The load current should be carried by the neutral CONDUCTOR and not any ground conductor (ground rod). What you call the reference is a very good description of the bond between neutral and ground. The ground should be able to carry current back to the neutral IF NEED BE. But that's it, never anytime else. Your case proves something different which is why I said it was a scary installation.
 
  • #25
Averagesupernova
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Averagesupernova, I noticed your power supply wires are Aluminum? What's the Code in your country?
Here in the US everything above a certain size is aluminum. Not sure what that size is. I don't think any circuit run in a normal residence is aluminum, they are all copper. At least that's the way it is in my locality.
For instance, the 50 amp range circuit is still copper.
 

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