Hi,

Here is my dilemma: I have the symptoms of a "loose neutral"... that is to say, the voltage on all the receptacles on one particular circuit in the house will drop to as low as 101 VAC when a large load (AC compressor motor) is applied. Subsequently, all of the lights on that circuit will dim as well. Meanwhile, the other circuits in the house maintain a steady 120VAC and their lights do not dim, thus eliminating the possibility of the problem lying upstream of the main power panel.
A troubleshooting tip I found online recommended I check each of the receptacles in the faulty circuit for a bad neutral connection. So, I started going around the house, pulling off covers and checking neutral connectivity. The first few outlets were as I suspected: The 120VAC could be read from the Black (B) wire to White (W) wire, and again from black to ground (GND). White to ground read 0 ohms. So far, so good... However, once I got to the master bedroom, things started to get strange...
I pulled all of the outlets belonging to the faulty circuit and started checking them; all of them read the same thing: 55VAC B-GND and 25VAC W-GND, 120VAC B-W, and W-GND read infinite ohms. The neutral wires were not connected to the neutral bar at all... instead, they had voltage on them!
Furthermore, on one of the outlets I found two black wires connected together by a wire-nut on the hot side of a receptacle (we'll call them B1 and B2) and one white wire coming in and connecting to the neutral side. B1-GND, B2-GND, and W-GND read approx. 55VAC, 25VAC, and 25VAC respectively. B1-B2 and B1-W read 120VAC, and B2-W read 0V. I then turned off the circuit bkr and checked resistance readings. B1-B2-W read 0 ohms. W-GND read infinite ohms (open). I left B1-B2 disconnected and went back to the previously checked outlets in the other rooms. None of the lights worked and none of the outlets had any power whatsoever. Once I reconnected B1-B2 together, all power returned to the circuit: lights came back on and outlets read normal. Keep in mind that all of the other receptacles on the circuit - with the exception of the three in the master bedroom - read as follows: B-W = 120VAC, Infinite ohms. W-GND = 0VAC, 0 ohms. <-- from my research, I assume that this is as it should normally read.

My question is, what is going on with my masterbedroom wiring? Thanks/ Kathleen

I pulled all of the outlets belonging to the faulty circuit and started checking them; all of them read the same thing: 55VAC B-GND and 25VAC W-GND, 120VAC B-W, and W-GND read infinite ohms. The neutral wires were not connected to the neutral bar at all... instead, they had voltage on them!

If you had pulled all of he loads on that circuit, the 55 Vols would have gone away.

Suppose that on a piece of equipment this filter was on the power input line. B Series (http://www.corcom.com/Series/PowerLine/B/)

Note that there are leakages to ground because caps don't have infinate resistance. Your meter has > 10 M ohms input imedance, so it can see that voltage. The opened lead is driving, say the neutal of the outlets downstream with a weird reactive voltage divider. ~ 1/2 the line voltage is a dead giveaway. The 55 VAC could only supply about a mA or so. It would not drive a 120 V incadesent lamp at 55V. If you connected the lamp, the voltage across it would drop to nearly zero.

Resistances measured with an ohmeter generally should not be trusted as a correct value. Also remember to subtract out the resistance that you get with the leads shorted. High resistances, say > 100 Mohms and resistances less than an ohm require different techniques to get an accurate values.

The question comes up once in a while.

Hi! Kathleen, and Welcome to AMHD :)

That's is interesting... My first thought was a three-way switch that was taken out of service.
The question would be where? but I'm not 100&#37; sure this is the problem.
I'm going to do some more checking, so hang in there. One of our other members should be along shortly.

I have a mystery myself... 3gang switch box, all switches wired, but only the outside two control service... doesn't matter if the middle's on or off, the other two work. :confused:

I'll be checking back

Steve

KeepitSimpleStupid,

Thanks for the post! So what you're saying, if I'm reading your response right, is that there is a load I have not yet discovered that is connected in line with my circuit, thereby dividing the voltage at some point... As far as the neutral not being attached to ground goes, I didn't quite understand the explanation. However, you bring up a good point in that I should probably invest in a megger for more accurate testing.

Tks,

K

Look at this .PDF where the schematic is located. http://www.corcom.com/pdf/B.pdf

This is a part that attenuates RF fequencies.

If you were to take that part and connect the inout like it's supposed to be connected, but leave the ground wire off and measure at the output relative to ground at the output. You'll end up with that voltage on the ground terminal (1/2 the input).

Now pretend that that's feeding an outlet strip or multiple outlets. They (downstream) will all act that way until the ground/neutral is fixed.

Morning, KeepItSimpleStupid an poulsbonian

I'm just trying to understand here, and I didn't want to hijack her thread.
something-mysterious (https://www.askmehelpdesk.com/electrical-lighting/normal-120vac-something-mysterious-382758.html)

The only RFI Line Filters I'm used to are the ones you use in cars to control static on the audio players.

If I understand correctly:
When a large load is applied the power drops and the lights dim.
You take a reading and find half the rated voltage.
This tips you off that it is a line-filter leaking.

I have never seen these units in-line with any major appliances.
Would it be safe to assume that the RFI filter is a design feature, and is incorporated into the circuitry of the appliance? And as it seems to me, you are suggesting there is an incorrect/insufficient ground at the appliance that causing this?

Somewhat :confused:... k

I merged the last post to the ongoing thread, as they are related.

Having a tough time myself trying to follw this thread.

I get an air conditioner is on a general purpose lighting circuit in a bedroom.

AC starts and the volts dip to 101 Volts, and light blink or dim.

OK, so? That is normal. The AC should be on it's own dedicated circuit.

The bedroom circuit is probably a 15 amp circuit with #14 wire. #14 wire may be too small for the starting current of the AC, and voltage drop, due to wire size and possibly distance is contributing to the normal voltage sag that occurs when the AC starts.

Then testing of the outlets is done, with an Ohm meter and the neutral is disconnected at the panel? Why? An open neutral with devices in the circuit will cause voltage to be measure on the neutral.

Then an RF filter is mentioned? What does that have to do with anything?

Your going to invest in a Megger? For what? A Megger is designed to measure meg-ohms of a cable, motors, etc to measure the integrity of the insulation, and CAN BE A DESTRUCTIVE TEST!

Someone help me out here. What am I missing?

What exactly is the problem?

Tk:

If you followed the thread which was hard to do, you would realize that the problem was fixed and the question morphed into "Where did the 55 VAC come from?.

I offered an explanation of why 55 VAC was seen on some outlets.

I've seen it. Suppose, that you had few pieces of equipment plugged into an outlet strip and one piece used a switching power supply. You measured about 60 VAC between a known good ground and the ground on the outlet strip.

In troubleshooting, the ground on the wall plug was non-existant. The RFI filter within a piece of equipment was dumping voltage onto the ground line. Since the fiilters are symmetrical, the voltage is nearly 1/2 the line voltage. That voltage is leakage and can only supply maybe 1 mA.

You thought the two different grounds together, they spark and that's it. No fuse is blown. 2 people tried to solve this problem for 8 hours together. I found it within 5 minutes.

OK, so looks like all is well.

I still don't get why the poster thinks they need a Megger.

Nothing to fool with, as it injects either 500 or 1000 volts, depending on the unit, the test being performed on what piece of equipment.

Just had yto get that warning out.

I will leave this alone from this point on, since you state the problem is fixed.

Thanks for the merge tkrussell, and so will I... Leave it alone, though interesting in how it works.