Hot/neutral suddenly reversed?

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  #1  
Old 03-19-07, 11:21 AM
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Hot/neutral suddenly reversed?

I have 3 questions:
1) WHat's the best way to test unknown hot/neutral wires?
2) Could installing a 220V line the wrong way cause other 110 volt lines to reverse hot/neutral?
3) What is the danger of having outlets with the hot/neutral reveresed?

Here's the background:
I removed my old stove which was hot-wired (no plug) with 3-wire/no ground BX cable. I noted which were the two hot wires and which ws the neutral - as indicated by their positioning as attached to the stove. After I removed the old stove, I turned back on the circuit breaker and re-tested the wires with a simple two-pronged tester (just indicates power, nothing more). Surprisingly, what I thought was neutral was actually a hot wire, and one of the hots was neutral. I tested this by touching one end of the tester prongs to a wire, then the other to the metal casing of the BX cable. I did this for each of the 3 wires, each time with one prong touching the metal casing. I've done this before with standard Romex cable (using the ground as the constant), with the idea that touching the neutral and ground wire shows no power - only hot and ground (or hot and neutral) shows power, and this is an easy way to deduce which is the hot wire. So, my first question is - is this an appropriate method of testing which is hot and which is neutral?

I then wired the new stove, using the neutral as identified by my test. Stove works fine. However, the ceiling fan/light in the kitchen, which is on a different circuit, now no longer works correctly. The pull switch for the light moves the fan now - and I can't get the light to go on. Using a receptacle tester on an outlet on the same circuit, reveals that the hot and neutral are now reversed. Testing a few other random outlets on different circuits shows that some are still ok, while some are reversed. This was not the case before I wired the stove.

I can easily go back and re-wire any outlet/switch that is now reversed, but I can't figure out how that could have happened. Is there any danger in having these outlets reversed? Could I have caused this by changing how the stove was wired?
 
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  #2  
Old 03-19-07, 11:32 AM
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You did not test for power properly. Never trust the conduit that wires are run in, be it rigid conduit or flex. I have seen far too many problems with conduit coming undone or failing to carry current to trust it.

You should have tested for power between each of the three wires. You should have used an analog meter or a two wire tester that would indicate 120 or 240 volts. That would have allowed you to identify the neutral.

I do not know what you did wrong, but I can think of several possibilities, none of the good. I suspect that you have an electrocution waiting to happen. I hope I am wrong.

I recommend that you disconnect the stove, immediately if not before. I then suggest that you properly test your existing circuits. Then properly identify the wires for the stove. Do this by tracing the wires back to the panel and looking where they terminate.

To answer your questions, since you asked them:

1. Trace the wires back to the panel and use a meter. Do not trust the conductivity of conduit.

2. Yes, and it could create an electrocution hazard.

3. If you really have the hot and neutral reversed (and I suspect you do not), the danger is that the wrong portion of an appliance or electrical device would be energized.
 
  #3  
Old 03-19-07, 11:45 AM
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Bob - thanks for the quick reply. As soon as I noticed issues, I turned off the circuit breaker to the stove, and have not turned back on. I will follow your instructions tonight when I get home.

You also mention tracing back the line to the box to see where each wire terminates. I'm a little confused by this - I have an old house, and the individual wires are cloth-coated, and not identifed with any type of ribbing, color, etc. I don't think there's any way for me to know which wire is which from each end. I just want to confirm this isn't absolutely necessary, and following your advice using a 2-wire tester will do.

However, I still have the issue of reversed hot/neutral on some circuits even with the stove circuit turned off. Any idea why this would be? It certainly was not the case before I started this project.

Lastly, could you please explain a bit more how a reveresed 220 line could cause other 110 line circuits to be reversed? I'd like to understand this better.

Thanks
 
  #4  
Old 03-19-07, 11:50 AM
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I second the instruction to shut power to the range off.

Let me guess, old house, you've just bought it, and a previous owner installed grounding receptacles that all test good with a receptacle tester.

I am concerned that your receptacles were not correctly wired, but instead used bootleg neutral or ground from the range circuit.

3 prong outlet testers can give very misleading results. You already understand about 'neon' testers. They will tell you if you have voltage between any two points. An outlet tester is simply three neon testers joined into a handy plug. The three lights indicate voltage between hot-neutral, hot-ground, and neutral-ground. The tester is simply telling you that voltage is present, and the pattern of voltage being present. It isn't telling you what wire connections have given you this result.

A neon tester doesn't give you a good idea about the voltage available, no the resistance in the system. A grounded conductor with a poor connection, energized by connected loads, could cause a neon to light.

After shutting power off to the range, see if any of the other problems change. Then trace out the range circuit, looking for junction boxes. Next check for correct voltage at the origination of the range circuit.

Finally, questions: how did the range that you replaced function? How did you test the new range? Does it heat, or have you determined that it is heating properly. (Note: if you connected 120V to the range, it will heat up, but not nearly as quickly as it should.) Do any of the problem indications change when the range is on?

-Jon
 
  #5  
Old 03-19-07, 12:05 PM
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Your guess is right - although many grounded receptacles show "open ground' with a 3-prong tester.

I'm almost positive the stove circuit is a "home run" to the jb - but I will check again.

Old stove worked fine - heated up quickly (for a 20-year-old stove). And the new one works fine too.

"Reversed" outlets do not change with the stove circuit on or off. That's the most troubling part - how could this tunred-off circuit still cause other receptacles to be reversed?
 
  #6  
Old 03-19-07, 01:07 PM
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Bootleg grounds are very, very dangerous. One simple failure could electrify things in your house that you touch every day. Don't delay getting this fixed.
 
  #7  
Old 03-19-07, 06:42 PM
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I just checked the range circuit - it is a straight run to the jb, so there can't be any "bootleg" neutral/grounds. I also checked the range wiring, and I have the 2 hots and neutral wires correctly identified. I am still having issues with the kitchen fan/light. What was the pull switch for the light now works the fan, and the fan pull chain only changes the fan speeds. This also all happened hours after I wired the stove. What could be the cause? I'd rather solve the larger problem than have to re-wire multiple outlets/lights.
 
  #8  
Old 03-19-07, 06:48 PM
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the two problems are not related. They just happed to happen near the same point in time.

If you are sure that the stove is wired correctly, next tackle the fan light.

I hate when this happens too. It just feels like the problems have to be related. But they often times are not.
 
  #9  
Old 03-19-07, 06:54 PM
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I may be trying to link two independent events - granted.

But how could the kitchen fan/light suddenly go haywire? I'm fine re-wiring, just want to make sure there isn't an accident waiting to happen.
 
  #10  
Old 03-19-07, 06:57 PM
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Originally Posted by MarcReyn View Post
But how could the kitchen fan/light suddenly go haywire?
They call it "planned obsolesce" it is designed into every consumer product in America.
 
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