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Old 12-08-2009, 12:38 AM   #1
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pos/neu reversed help please


Moved in to a house and began upgrading the AC sockets, old ones were so worn out that plugs would fall out of them.
We were very careful to maintain the hot wires on the hot side and the neutral wires on the neutral side.
After we completed the upgrades, turned the breaker back on, and put a Sperry 3 light tester on all sockets, all were correct.
Started to hook up the TV that went well, then when I went to hook up the CTV cable to the wall, I saw a 120V sized arc pop form the coax in my hand to the coax connector in the wall
Turned off the breaker, pulled the sockets back out, thinking there must be a short somewhere. Checked all the connections again, hot to hot, neutral to neutral.
I pulled the socket in question out, checked the socket again with the tester, and it read all correct. Well, long story short it took me forever to realize that the there is a switch on the wall that runs a socket, and a ceiling mounted light. When the light is switched on, the tester in a separate socket will read that pos/new reversed, when the switch is off, the tester reads correct.
Any ideas on what I can check here? I pulled the switch, it's two black wires, properly grounded, I opened the light and that was wired correctly as well.

Thanks so much
Michael

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Old 12-08-2009, 02:38 AM   #2
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pos/neu reversed help please


Were one or more of the old recepts only half switched, the top or the bottom? If so, they had the tab removed between the top and bottom - did you remove the tab on the new ones?

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Old 12-08-2009, 08:29 AM   #3
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pos/neu reversed help please


that sounds like a serious ouch. Is the tv fried?

what I suspect is, as vsheetz alluded to is that there was a 1/2 recep switched.

When using NM (Romex, what have you) cable, the white wire in the cable, at some point, is often used for a switchleg. If in the outlet box you were working in, if that was the case, then you may have either hooked a switched hot to the neutrals in the box and when the switch was turned on POP goes the breaker.


the worse case scenario involves a similar thing but if there were two different circuits used on the switched and non-switched sections of the recep and they were on different legs of the electrical service, you could have fed 240 volts to whatever was plugged into that recep if the one switched hot using the white wire was used as a neutral.

So, do you have an actual voltage tester available?

You need to undo the wire to that recep and very carefully energize them and test them each for voltage using a ground source for your other point of test.

If one of the white wires is hot, slip the switch and see if it goes off. If none of the whites are hot, flip the switch and see if one of the becomes energized.
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Old 12-08-2009, 09:38 AM   #4
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pos/neu reversed help please


Thanks for the reply -

I do have a volt meter, I'll check that - Amazingly enough the TV's perfectly fine If you need a new tv, buy a vizio!

We upgraded the receptacles a while ago, I don't *think* that any had the tabs broken (I know what you mean on the them) but that was a while ago. Volt meter seems the best thing to check.

All these issues are happening in just one room, and from what I can tell, the outlet the TV's plugged in to is the first, and from there it goes to switch and other outlets, so that one can't have it's tabs broken if I understand that process. Would it likely be the switched outlet? The switch itself has two black wires on it, and the two whites are pigtailed. On all the other outlets there's two nomex feeds in to the box, and I've kept them black to hot and white to neutral, making sure they are the same pair/wire for each outlet within the receptacle.

It will be very rewarding when this is all finished

Thanks again
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Old 12-08-2009, 10:45 AM   #5
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pos/neu reversed help please


You said the switch controls both a light and a receptacle.
What are the wire colors on the receptacle, and how is the light connected?
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Old 12-08-2009, 11:03 AM   #6
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pos/neu reversed help please


The switched outlet is one that we also replaced, but I can't recall if the old one had the tabs removed. The new one's tabs are still connected, and it's standard wired, black to the hot side, white to the neutral side.

I'm still very much a newbie when it comes to wiring, I think I know just enough to make sure the breakers are off before mucking with anything

But I am suspecting that maybe that outlet needs to have the tabs taken off? It's only when the light switch is turned on that I seem to be feeding AC back in to the circuit.

What's confusing to me though is that while we were upgrading the outlets, I did make the mistake once of getting the pos/neu wires crossed on an outlet, and the breaker would correctly trip as soon is it was flipped on, so this seems to be something different? That'd be nice if all I need is to break the tabs. I suppose I could test that by leaving a pair off of that switched outlet and test the switch?

Thanks!
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Old 12-08-2009, 01:10 PM   #7
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pos/neu reversed help please


Is the cable grounded at the building entrance? It should be tied to the building ground system not have a separate rod.

This could easily be a cable issue. Can you measure any voltage between the cable and the building ground?
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Old 12-09-2009, 09:35 AM   #8
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pos/neu reversed help please


Is the coax cable the only thing that sparked?

The problem could be unrelated to the electrical system work you did. The TV may have a erroneous connection inside causing exposed parts including the coax jack stud to be live.

You would want to do continuity checks between each plug prong of the TV and the coax jack stud. There should be no continuity between either flat prong and the stud and there may be continuity between the ground prong and the stud.

A reminder, do not do continuity (ohms) checking on a live circuit. Switch the meter back to AC volts first.
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Last edited by AllanJ; 12-09-2009 at 09:42 AM.
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Old 12-09-2009, 08:49 PM   #9
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pos/neu reversed help please


Quote:
Originally Posted by mtstreicher View Post
What's confusing to me though is that while we were upgrading the outlets, I did make the mistake once of getting the pos/neu wires crossed on an outlet, and the breaker would correctly trip as soon is it was flipped on, so this seems to be something different? That'd be nice if all I need is to break the tabs. I suppose I could test that by leaving a pair off of that switched outlet and test the switch?

Thanks!
I think you might have a problem somewhere. If the outlet is wired reversed it shouldnt trip the breaker. I have never seen a breaker trip just because the hot and neutral are reversed.
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Old 12-09-2009, 09:10 PM   #10
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pos/neu reversed help please


If you got a spark from the Coax, that has nothing to do with Hot & Neutral switched at the outlet, that has to do with poor grounding at the house. Not only can you fry electronic equipment, but the CATV company can shut off your service, charge you for damages for equipment in your home, along with the outside plant equipment on the line that your house is attached to.

Call an Electrician & the POCO to check out the house main Neutral, and internal wiring, before you have something major happen.
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Old 12-09-2009, 09:23 PM   #11
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pos/neu reversed help please


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Originally Posted by paul100 View Post
I think you might have a problem somewhere. If the outlet is wired reversed it shouldnt trip the breaker. I have never seen a breaker trip just because the hot and neutral are reversed.
Perhaps a grounded Neutral (which is common in old wiring) would do that (trip the breaker). I discussed a similar situation in another thread here. Stating that it's a common thing to find reversed hot/neutral in OOOld wiring. Additionally, there are grounded (or shorted) Neutrals. (No matter what) Don't drink and Drive, Ever!!!
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Old 12-10-2009, 01:17 PM   #12
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pos/neu reversed help please


As far as poor grounding in your house goes, you can do some tests yourself. Take a length of single conductor #14 wire, enough to stretch through several rooms. Connect one end to a known ground, for example the ground bar in your main panel. Take the other end about the house and measure voltage between other things (such as the coax cable screw on cap) and the ground wire end. While you are at it, you would want to see that your electrical system is properly bonded to the plumbing system (a #6 wire for services up to 100 amps connected permanently from the panel ground bus bar to the main water pipe where it exits the house for the water main underground.)

Using a pipe in the nearest bathroom cannot be assumed to be a ground since the piping going down to the basement might be plastic part of the way.

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