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-   -   Circuit tester shows open neutral; multi-meter says something different. (http://www.diychatroom.com/f18/circuit-tester-shows-open-neutral-multi-meter-says-something-different-55857/)

fredgmeyer 10-24-2009 08:47 PM

Circuit tester shows open neutral; multi-meter says something different.
 
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.

EBFD6 10-24-2009 09:13 PM

With those voltage readings you most definitely have an open neutral. You need to recheck all neutral connections from the panel out to the receptacles having issues and find the loose/broken connection.

mpoulton 10-24-2009 09:28 PM

Quote:

Originally Posted by fredgmeyer (Post 345032)
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.

You have an open neutral. Your digital multimeter is reading capacitively-coupled voltage on the disconnected neutral wire. This is to be expected. If you use an analog meter or a low-impedance digital meter, it will read 120 H-G, 0 H-N, and 0 N-G. If you measure resistance from N-G, it will read "infinite" instead of 0 like it's supposed to.

Irrelevant science content:
Interestingly, note that 87+30=117, pretty close to 120. The neutral wire is floating at a voltage determined by its physical proximity to the hot and ground conductors. It is more closely coupled to ground than to hot, since the ground wire sits between the hot and neutral in a romex cable.

joed 10-24-2009 09:41 PM

You have an open neutral. Problem could be in any box on the circuit (light, switch, receptacle) even if the device is still working. It could be in the main panel as well if the entire circuit is dead. One of the most common causes of this is back stabbed receptacles.

kbsparky 10-24-2009 10:08 PM

First thing to check: Are there any outlets on this same circuit that are operating normally? If so, find the last properly working outlet on the circuit, and check the connections THERE. I have discovered that such problems are more likely to originate from a working outlet, than a non-working one.

fredgmeyer 10-24-2009 10:11 PM

Thanks for the replies so far. Still testing.
 
And watching college football.

A follow up: if the problem is a loose neutral connection at one of the receptacles or fixtures at some midpoint of the circuit, will that affect only what is downstream of the loose connection, or will it knock the whole circuit out entirely? Because it appears the entire circuit is problematic (i.e., the weird voltage readings at every receptacle that I put the multi meter to.

EBFD6 10-24-2009 10:28 PM

Quote:

Originally Posted by fredgmeyer (Post 345054)
And watching college football.

A follow up: if the problem is a loose neutral connection at one of the receptacles or fixtures at some midpoint of the circuit, will that affect only what is downstream of the loose connection, or will it knock the whole circuit out entirely? Because it appears the entire circuit is problematic (i.e., the weird voltage readings at every receptacle that I put the multi meter to.

If the bad connection is in a device it would affect anything downstream from the problem. If the whole circuit is problematic I would start looking at the panel.

spark plug 10-24-2009 11:12 PM

Quote:

Originally Posted by fredgmeyer (Post 345054)
And watching college football.

A follow up: if the problem is a loose neutral connection at one of the receptacles or fixtures at some midpoint of the circuit, will that affect only what is downstream of the loose connection, or will it knock the whole circuit out entirely? Because it appears the entire circuit is problematic (i.e., the weird voltage readings at every receptacle that I put the multi meter to.

Let me put my Two Cents in, too. (After all the other posts, there's practiclally nothing left to say). I would be inclined to say that there is a grounded Neutral in one of the receptacles.But the connection is not strong (Corrosion on the Neutral?).Also, I have Zero confidence in those Plug-in Circuit testers. (No matter what):yes::no::drink:Don't Drink and Drive, Ever!!!

Yoyizit 10-25-2009 03:21 PM

Quote:

Originally Posted by mpoulton (Post 345046)
capacitively-coupled voltage on the disconnected neutral wire.

If you use an analog meter

It's about 100 picofarads of capacitance per foot of Romex.

With an analog meter, the reading depends on the ohms/volt sensitivity, and will change as you switch scales, the reason being you are reading the open circuit voltage of a quasi-current-source.

fredgmeyer 10-25-2009 07:08 PM

Thanks again, and here's what I was able to find...
 
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.

Weird. Thanks again. Any insight into what might have caused the singed neutrals or the malfunctioning fixture downstream would be greatly appreciated.

Steelhead 10-25-2009 10:26 PM

I've seen that problem with the light bulbs before. Sometimes the tab at the bottom of the light socket is pushed in too far and not making contact with the end of the bulb. Make sure there is no power to the socket and pry that tap towards you a little. See if that doesn't solve your problem.

spark plug 10-26-2009 01:41 PM

Fredgmeyer (Poster #10) I'll address your concern about the ceramic light fixture, on which some bulbs (that work in other light fixtures) don't work here. I've had a similar experience with a Rubber Pigtail Socket. Where some Incandescent lightbulbs (usually of a lower wattage, due to their smaller physical size) did not work, while they worked on other fixtures. The cause might be that the bulbs don't reach the center "Button" on the base of the socket. Eliminate confusion :yes::no: through Education; Don't Drink and Drive, Ever :drink:!!!


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