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Circuit tester says open neutral, multi-meter shows weird readings

Circuit tester says open neutral, multi-meter shows weird readings

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  #1  
Old 10-24-09, 05:42 PM
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Circuit tester says open neutral, multi-meter shows weird readings

A circuit in my house suddenly stopped working - no tripping of a breaker, GFCI, smell of smoke, etc. There are about 6 outlets, one smoke detector, two switched ceiling fixtures, and a ceiling fixture on a three-way switch on this circuit.

First thing, I tested all the outlets with voltage tester - this appeared to show that BOTH hot and neutral sides had voltage. Then, I used a 3-prong circuit tester which showed "hot/ground reversed." After doing some homework about the limitations of these circuit testers, I removed every load on the circuit (which at this point, was only a couple light bulbs). I re-tested the outlets with the 3-prong tester and now it shows "open neutral."

I've checked ALL the wire connections in the outlets, and they appear to be solid. Finally, I used a multi-meter on the outlets, and here's where it gets kinda weird...for all of the outlets on the circuit, this is what I'm showing:

Hot to neutral: about 87 volts
Hot to ground: about 120 volts
Neutral to ground: about 30 volts

At this point, I have no idea what is going on. Is there a loose neutral connection? Why the voltage between neutral and ground? I'm lost.
 
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  #2  
Old 10-24-09, 06:04 PM
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Are you using a digital multimeter? If so your readings except the 120v may be phantom/ghost voltage. If any of the connections are back stabbed they should be moved to the screws.

The 87 volts might be real but the 120v to ground indicates a loose neutral at the very least.
 
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Old 10-24-09, 07:37 PM
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As Ray suggested, it may be a loose neutral and he is probably correct... 9 times out of 10 I have always found that the neutral is loose or not hooked up when I get that reading on my tester. Also by reading with a multimeter, if you get the correct voltage on hot/ground and somewhat lower on hot/neutral that will pretty much confirm it. I would go to one device, preferably the device in the middle of the run if you can guess that and see which one, if any gets a correct reading on hot/neutral and maybe determine where the problem is before you tear everything apart. Keep in mind lots of electronics are very sensitive to losing a neutral and they might actually burn up if you try to run them with one missing or loose. I have seen plenty of tv's burn up just for that reason. If you have problems finding it I suggest you call an electrician to diagnose and fix the problem for you. Best of luck.

-Paul
 
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Old 10-24-09, 11:54 PM
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Pretty much classic sign of loose netural and what more with digtial meters they are very senstive to pick up inductive voltage aka ghost voltage to get the DVM reading wrong so what you need to do is start at the last working device along that circuit and work it way down I know it will not be easy but this is the safest way to do this and make sure you have the power off first before you remove the device out of the junction box.

Most common cupit is backstabbed recepatle that useally most common casue of loose netural situation so move them from back stabbing to screw or backwired { with screw clamp type }
And it will be good idea to check the rest along the circuit sometime you may get more than one show up.


Merci.
Marc
 
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Old 10-25-09, 11:54 AM
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It's possible to have a Neutral-to- Ground reading of 30 volts if , say , the Neutral current = 10 amps , and the resistance of the Neutral conductor between the outlet and the panel = 3 Ohms, giving a 30 volt drop in the Neutral conductor from the panel to the outlet.

With +120 volts at the panel , the sum of the voltage drops across circuit is -90 volts across the load , + -30 in the Neutral, = -120 volts.

+120 volt "rise" + -120 volt "drop" = 0 which is a basic circuit "Law"
 
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Old 10-25-09, 12:46 PM
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Originally Posted by morpheusoptic View Post
I have seen plenty of tv's burn up just for that reason.
How, if it is not on a shared neutral circuit?

And say if also the neutral that was lost, was not at the main or outside the house (where it could backfeed up the other leg), but was at some outlet on just one leg, -

-wouldn't the circuit just have lesser voltage?, or none at all? Or, could it be that lesser current going to a tv is harder on it than some overcurrent?
 
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Old 10-25-09, 09:06 PM
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Thanks for all the suggestions.

To answer a question, I was using an analog meter...I probably need to go out and get a digital meter one day.

So this is what I end up finding...

Since the entire circuit was bad (nothing was working, and all outlets and fixtures were showing the same weird voltage readings), I checked the neutral connection at the panel, and it was rock solid.

So then I followed the circuit to the first fixture (one of those pull-chain ceramic bare-bulb fixtures) and found a branch circuit coming off that fixture's j-box, in addition to the main circuit continuing downstream). So basically there were three penetrations of Romex into that box, and therefore four neutrals wire-nutted together (the neutrals from the three Romex penetrations plus the fixture's neutral.) The connections looked twisted together very solidly...HOWEVER, something was amiss. The wirenut (which looked plenty big for the four wires) was slightly melted, and a couple of the neutrals were pretty badly singed. I saw no evidence of bare wire exposed beyond the wirenut, or any evidence that the neutral had made contact with the metal shell of the j-box.

Anyway, I removed the melted wirenut, clipped away the singed ends of the neutrals, and re-did the connection with a new wirenut, and then taped the open end of the wirenut. That done, the circuit appears to be OK now (normal voltage readings from H-N, H-G, and N-G...with one weird exception - another downstream ceiling fixture (same ceramic, pull-string type) won't operate some of the light bulbs I put in it. I've tried a couple CF bulbs which won't work and a couple filament bulbs (some of which do work and some of which don't). Bulbs that don't work in that fixture do work in other fixtures on other circuits. I checked H-N voltage in that fixture and it is normal.

Kinda curious about the singed neutrals...if it was an issue of current overload overheating the neutrals, why didn't the breaker trip? It's a 15 amp circuit...shouldn't the wires be rated to handle that? (The whole house was professional rewired about 3 years ago).

I'm guessing the problem with the fixture is the fixture itself and I just never noticed it before...but for whatever reason, the same bulb that was working in that fixture before I had this whole circuit issue will not work in the fixture, but others will. Might just be bad contacts that got aggravated when I removed the fixture.

Thanks again.
 
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Old 10-25-09, 09:13 PM
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To answer a question, I was using an analog meter...I probably need to go out and get a digital meter one day.
NO. An analog is best.

The wire nut probably melted because of a bad connection inside of it.

Check the tab in the bottom of the fixture that doesn't always work. Is it corroded or to flat? With power off at the main panel bend it up slightly and clean if needed.
 
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Old 10-26-09, 08:16 AM
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Originally Posted by fredgmeyer View Post
To answer a question, I was using an analog meter...I probably need to go out and get a digital meter one day.
Originally Posted by ray2047 View Post
NO. An analog is best.
I respectively disagree. I use exclusively a digital meter in my job. It is a Fluke 7-600. It is the easiest meter I have ever used. I never have any problems with any ghost voltage readings. (other than maybe .5 volts) Fluke 7-600 Electrical Tester Sadly it has been discontinued but I guess there is a replacement model.

The only time I have issues using my digital meter is working on trailer lights because the display will not react fast enough, but this is a once a year event.
 
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Old 10-26-09, 08:37 AM
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The CB would not trip on an overload because the defective connection was a form of resistance. Adding resistance to a circuit causes opposition to current flow.

What the resistance can do is cause heat ; even though the current in the circuit is reduced, with the heating effect , measured in Watts at the defective connection, proportional to the square of the current.

If the current was only 5 amps , and the resistance of the defective connection was 4 Ohms, the heating effect would be ( 5 X 5 ) X 4 = 100 Watts.
 
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Old 10-26-09, 09:40 AM
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I respectively disagree. I use exclusively a digital meter in my job. It is a Fluke 7-600. It is the easiest meter I have ever used. I never have any problems with any ghost voltage readings.
Toyln I don't disagree for an experienced user. I also use a digital. It's just that newer users may not understand the reading or be misled. I perhaps should tone down my recommendations. Point taken.
 
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Old 10-26-09, 11:27 AM
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Originally Posted by ray2047 View Post
Tolyn I don't disagree for an experienced user. I also use a digital. It's just that newer users may not understand the reading or be misled. I perhaps should tone down my recommendations. Point taken.
Your point is taken as well. I should have figured that not too many DIYers will drop $100+ on a meter.
 
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Old 10-27-09, 09:59 AM
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As explanation for reading 30 volts Neutral-to-Ground ---

When making this type of test, the Grounding Conductor from the panel essentialy forms a "link" between the meter test-lead and the Neutral connections in the panel. Zero current in the Grounding Conductor = Zero voltage across the GC.

The other test-lead is applied to a Neutral Conductor that extends from the panel , with XC amps current thru the Conductor. In between the two meter test points there is XR Ohms in the Conductor , causing the meter to indicate a voltage-value equal to XC amps X XR Ohms.
 
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