Line fault at the outlet -- do I need an electrician?


Yesterday, I got a Panamax, Max 1500 surge protector and line conditioner. (I got a very good deal on it, and am just trying it out.)

I plugged it into an outlet I've been using for a while and one of the red lights on the front lit up saying "line fault." (I'm not sure how this is different from a "ground fault." Maybe it's the same.) The Panamax does not do this with other outlets in the room. They seem ok.

So, I know this means that the outlet is improperly wired. My question is, might this be a simple thing to check and/or fix? Any suggestions most appreciated. It's the only outlet I can use to have my audio set up where I usually have it. Now is not an optimal time to call an electrician. If this is a big problem, I'll try out my gear somewhere else in the room, but if I can fix this without too much expertise, that would be ideal.
8700e65e 845e 4b1b 91cc df27687f9454hilde45
 Could just be that the outlet is wired wrong. Go to Home Depot or Lowes and buy a plug in tester. It will check polarity, open ground etc.
Is it a GFCI receptacle or is there one in the room?
No, it's not GFCI, just an outlet run down from another one in the room.

I could get a tester if that could tell me that what is wrong is something I could fix myself (assume I have no knowledge, except to turn off the breakers). The Panamax is already showing that it's reading below 115 v and has a fault of some kind.
It usually means the receptacle is wired wrong or wire is loose  or is bad.
"The Panamax is already showing that it’s reading below 115 v and has a fault of some kind."

- Does it read higher voltage in the other outlets?

115 is getting to the low end for North America, but still in limits. However, if it says 115 on one outlet, then say 120 if you immediately move it, and 115 when you immediately move it back, that is troubling. That means a poor connection, not just a miss connection. That should be addressed quickly.
Yes, likely receptacle is wired in reverse polarity. Turn off breaker, dislodge receptacle, check it out. The plug in testers are nice. You might want to test other outlets in your home. 
"Does it read higher voltage in the other outlets?"
Yes. I'll compare different outlets and stop using the bad one.
Thanks, Mesch. I'll test.
If you’re ok with pulling the outlet cover off and shining a flashlight in on both sides you may be able to see the hot (black) and neutral (white) wire going to the side screws, or if it is a back-stab connection you may be able to see which side black goes to and which the white goes to.  These wires need to be on the correct color screws on either side. ( Silver screw and brass screw. )

see attach link for details if you live in the US.  
https://i.pinimg.com/originals/a4/ba/86/a4ba86ca2eaa2d769727076a912e4452.jpg
If the colors are reversed from the image you have reverse polarity at the socket.  If correctly wired, as mentioned above you may have a loose screw connection or defective back-stab connection.  All are relatively simple corrections if you’re comfortable turning off breaker and redoing the wire connection.  Electrician is the certified answer but a quality handyman is quite capable of the same job at a lesser cost if you’re not up for the task.  
Thanks, Bryhifi. I think I could at least take a look. It's two different outlets that have the fault -- one feeds the next one. I wonder if correcting the root might also correct the branch.
hilde45,  that is a possibility if the feed going to the line side of the first outlet is reversed and the daisy chained outlet is wired in parallel off the load side of the first outlet in correct polarity. 

https://solitum.net/content/images/2015/08/62304C67F7C8465FB3B153929E16E752.jpg
Yes, it's usually the first one that needs fixing which fixes the next in line.
I would get that plugin tester for the rest if the house anyway and make your job easier.
Good luck
@bryhifi I have a digital multimeter. I use it to test car batteries. I suppose I might use that, too, no? In any case, I can get the three prong outlet if necessary. Thanks for the picture you sent -- I've saved that.

@cissado @heaudio thank you for your advice, too. 
hilde45 OP269 posts

03-20-2020
7:26am

@bryhifi I have a digital multimeter. I use it to test car batteries. I suppose I might use that, too, no? In any case, I can get the three prong outlet if necessary.

The DMM will work just fine.

1) Set the meter to AC ~ auto volts or an AC ~ voltage scale above 150Vac.


2) Insert one test lead probe in the "U" shaped equipment ground contact hole of the wall outlet. Make sure you make good contact to the ground contact. Insert the other test lead probe into the Hot contact slot of the outlet. Make sure you make a good connection to the Hot contact. (The Hot contact is the smaller of the two slots.) You should read 120Vac nominal volts. *(If the reading is bouncing all over the place that is what is called a phantom reading, not a true reading.)
If you get a solid good 120V nominal reading that will tell you two things. The AC polarity is correct and a ground is present.

IF you do not measure 120 Volts nominal. That can mean Two things.. NO equipment ground, or Hot and Neutral reversed polarity.

3) Measure for voltage from the equipment ground contact to the neutral contact. The neutral contact is the larger of the two slotted holes on the outlet. Make sure the two DMM probes are making good contact. If you measure a good solid 120 nominal voltage then the Hot and Neutral branch circuit wires are reversed on the receptacle outlet. If you do not measure any voltage then you do not have an equipment ground.

Jim

.
"3) Measure for voltage from the equipment ground contact to the neutral contact. The neutral contact is the larger of the two slotted holes on the outlet. Make sure the two DMM probes are making good contact. If you measure a good solid 120 nominal voltage then the Hot and Neutral branch circuit wires are reversed on the receptacle outlet. If you do not measure any voltage then you do not have an equipment ground."

I think some clarification here for a novice. When you measure between ground and neutral at a receptacle, most multimeters will indicate some voltage, i.e 0.1 - 2.0V approx.
That's fantastic -- thank you so much. It's a snowy day in Denver today and I am shut inside. I'm printing this out for reference. 
heaudio123135 posts  

03-20-2020  
 8:58am  

"3) Measure for voltage from the equipment ground contact to the neutral contact. The neutral contact is the larger of the two slotted holes on the outlet. Make sure the two DMM probes are making good contact. If you measure a good solid 120 nominal voltage then the Hot and Neutral branch circuit wires are reversed on the receptacle outlet. If you do not measure any voltage then you do not have an equipment ground."

I think some clarification here for a novice. When you measure between ground and neutral at a receptacle, most multimeters will indicate some voltage, i.e 0.1 - 2.0V approx.

heaudio123
I think some clarification here for a novice. When you measure between ground and neutral at a receptacle, most multimeters will indicate some voltage, i.e 0.1 - 2.0V approx.


True, If #2 of my previous post above is met. Therein a properly wired receptacle outlet with a Correct AC polarity, and an equipment ground is present.

For the novice a difference of potential, voltage, measured between the neutral conductor and the equipment grounding conductor on branch wiring can be caused by, at least, two things.

1) VD, (Voltage Drop), on the neutral conductor due to the connected load on the branch circuit.

2) An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor.

Jim
Ok, here are some results.

TESTS for two connected outlets:
Ground contact of wall outlet TO Hot contact slot = 4 volt reading
Ground contact of wall outlet TO Neutral contact slot = 120 volt reading

TEST for another outlet on a different circuit in same basement:

Ground contact of wall outlet TO Hot contact slot = 124 volt reading
Ground contact of wall outlet TO Neutral contact slot = 0 volt reading

I suppose this means I have reversed polarity on those problematic outlets?
I don't know why I got a 4 volt reading in from those outlets.

Hopefully you fix the last receptacle in the circuit, otherwise you'll have to change out the rest because they'll now be reversed. 
Well, it seems you've done it. Congrats.
Oh, I misread. You just need to reverse one, then the next one in line will be fixed.
@cissado -- I would need to reverse the initial one, no? Or perhaps it's messed up all the way back at the box? I am shying away...
This first one is reversed pull it out and see if the white wire is on the bronze screw side and black wire on the silver screw side which would be wrong. If not look at the receptacle prior where it's  drawing power from for the same thing. Black to bronze, white to silver, bare wire to green screw is how they should be. 
@ hilde45 OP

As djones51 said, start with the wall duplex receptacle you tested that has the reversed polarity. (Hot and neutral wires reversed on the outlet device.)

Make 100% sure the breaker that feeds the outlet is turned off. Plug a lamp into the outlet. Turn the lamp on. The bulb lights. Go turn off the breaker. The light bulb is no longer lit. Use your mulimeter to verify the outlet is DEAD.

Carefully pull the duplex outlet from the wall box. HOPEFULLY there is only three wires connected to the outlet device.

If more than 3 wires connected to the outlet device,... stop..... Do not proceed.... Draw a picture on a piece of paper showing exactly how the device is now wired noting exactly how and where each colored black and white wires are connected on the outlet device. Make sure to note if the black and white wires are only connected to the side screw terminals. Or maybe also stabbed in the back into quick connect pressure terminals.

Post back you findings.

Note, for the branch circuit wiring:
(Per NEC there shall be only one equipment grounding wire connected to the equipment ground terminal on the duplex receptacle outlet device. All equipment grounding conductors within the outlet box shall be joined/jointed together with a pigtail extended out for connection to the duplex receptacle device.) If the outlet box is metallic, made of steel, the box shall be grounded as well.


djones511,315 posts

03-21-2020
12:19pm

This first one is reversed pull it out and see if the white wire is on the bronze screw side and black wire on the silver screw side which would be wrong. If not look at the receptacle prior where it’s drawing power from for the same thing. Black to bronze, white to silver, bare wire to green screw is how they should be.

@ hilde45 OP


You will also notice the color of the terminal screw heads are on the same side of the Hot contact (small slot), and neutral contact (longer slot), of the duplex outlet.


If you acknowledge, post, you have read this today I will check in on the thread through out the day. You can also PM me through the Agon system if you so choose as well.

You are not required by the NEC or possibly/more than likely by your AHJ (Authority Having Jurisdiction) in your area to be an electrician to change out an outlet. I would strongly suggest though you feel confident that you have the know how to do it though. IF in doubt hire an electrician.

Jim
Thanks, Jim. Later today, I will probably try this. Or tomorrow.

Before I proceed -- I want to be clear that so far I have tested multiple outlets on this daisy chain -- they all read as reversed.

I do not yet know how far back they go. 

QUESTION: Are you suggesting that I try to *just* deal with the outlet nearest my gear? Or are you saying that I should deal with something at a prior step in the chain (nearer) to the breaker box?
I would follow Jim's advice but you may want to start at the beginning and pull the cover off the panel box and JUST LOOK to see that the wiring on the circuit breaker matches all others. DO NOT TOUCH ANYTHING IN THE PANEL BOX! If possible you can always turn off the main power breaker coming into the panel to do this. Sometimes homeowners add a circuit (I added a dedicated 20 amp circuit to mine) and they may have wired it wrong. I highly doubt that's the case but it is possible. By the way, if you kill the main breaker, be sure to have a flashlight in your hand.
It’s two different outlets that have the fault -- one feeds the next one.

This right here is the single biggest problem with audiophile quality power: the daisy chain. When running a dedicated line this is the biggest benefit by far, the elimination of all these extra connections in the power path. Its not so much that voltage improves, although in your case it sounds like it might, but the elimination of a lot of connections and all the micro-arcing and eddy currents that go along with them.

DO NOT TOUCH ANYTHING IN THE PANEL BOX!


Right. Whatever you do, do not remove the inner panel cover. Do not remove all the circuit breakers. Do not paste expensive goo all over the bus bars. Do not connect anything other than to code. No matter how good it makes your system sound. Just don’t. Lol!

Oh and whatever you do, DO NOT run 240V to a step down transformer, and hard wire it to a home brew mess of a conditioner. DO NOT DO THIS! ROTFLMFAO!
https://systems.audiogon.com/systems/8367
Thanks for the safety suggestions, all. I aim to have a dedicated line but that has to wait on some home renovations. At the moment, I just want to locate my gear where the shelves, etc. are -- but that's where the weird outlets are. I'll be careful.
It does sound like your wiring is reversed.... but!!!

It may also be you have a bad neutral.  The 4 volts should be zero. It indicates you have higher than normal resistance on that wire.  This could happen from bad screw connections or bad twist-on connector.

When you finish reversing, check again. If still 4 volts, chase that down.
If your circuit comes from a sub panel, the 4 V may need you to get an electrician.  I'm not sure what the requirements are, whether 4V is OK, but it does signal higher than necessary resistance, and that means you'll be ever so slightly power constrained.
@Hilde45, when you measured the 4 volt difference between safety ground and the miswired "hot" terminal on the outlets was some or all of the equipment plugged in at the time? If so, I think it would be worthwhile to repeat that measurement with the equipment unplugged. In addition to the possible causes Erik has cited for the 4 volt measurement I’m thinking that applying 120 volts to the neutral of whatever equipment was plugged in could have resulted in AC leakage to ground within the component(s) that might have been responsible.

Jim ( @jea48 ), does that sound plausible to you?

Good luck. Best regards,
-- Al

hilde45 OP283 posts   

03-22-2020   
 12:14pm   

Thanks, Jim. Later today, I will probably try this. Or tomorrow.

Before I proceed -- I want to be clear that so far I have tested multiple outlets on this daisy chain -- they all read as reversed.

I do not yet know how far back they go.

QUESTION: Are you suggesting that I try to *just* deal with the outlet nearest my gear? Or are you saying that I should deal with something at a prior step in the chain (nearer) to the breaker box?


@ hilde45

I had only read this far in your last post:
Thanks, Jim. Later today, I will probably try this. Or tomorrow.
When I then responded Ok.....

I just checked your thread and read the rest of your post.
Before I proceed -- I want to be clear that so far I have tested multiple outlets on this daisy chain -- they all read as reversed.

I do not yet know how far back they go.
Keep checking..... Keep checking the outlets on the circuit as you get closer to the electrical panel you will find the culprit. The chance the problem is in the electrical panel is slim to none, imo.

Jim
Thanks, Erik, almarg, jim — thanks.

So, our house is a mixture of old/DIY and new (renovation); the problem is with the old part of the house.
Almarg — I have not tried measuring with everything on the chain unplugged. I'll do that when possible.
As far as finding the outlet closest to the panel is a bit tricky, as the wire which feeds things disappears into the ceiling and I'm not sure where it goes first. I'm sure where the 3rd, 4th outlets are, but not the 1st, 2nd ones. If the problem was at the panel, that's at least clear. If it's not at the panel, then I suppose I can just *try* what might be outlet #1, first, and see what I find.

I'd love to avoid opening the panel, but from what I gather, this is not so hazardous if I'm only looking.
almarg9,456 posts

03-22-2020
2:11pm

@Hilde45, when you measured the 4 volt difference between safety ground and the miswired "hot" terminal on the outlets was some or all of the equipment plugged in at the time? If so, I think it would be worthwhile to repeat that measurement with the equipment unplugged. In addition to the possible causes Erik has cited for the 4 volt measurement I’m thinking that applying 120 volts to the neutral of whatever equipment was plugged in could have resulted in AC leakage to ground within the component(s) that might have been responsible.

Jim ( @jea48 ), does that sound plausible to you?

I’m thinking that applying 120 volts to the neutral of whatever equipment was plugged in could have resulted in AC leakage to ground within the component(s) that might have been responsible.

Jim ( @jea48 ), does that sound plausible to you?
Al, (almarg), yes I would think that is a possibility too. Any connected load along the entire length of the branch circuit.


Also as I said previously.
1) VD, (Voltage Drop), on the neutral conductor due to the connected load on the branch circuit.

2) An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor.
4Vac would be pretty high in my opinion though.

Here is another possible reason:
IF there was a decent size load connected to the circuit at the time the 4 volts was measured it could be caused by a slightly loose and or corroded neutral connection anywhere from the panel neutral bus connection to the outlet the OP measured the 4 volts.

It would be interesting to know if the other branch circuit the OP measured 124Vac on is fed from the same Line,Leg, as the circuit he is experiencing the problem on. If yes, the 4V could very well be caused by a slightly loose and or corroded neutral wire connection in the branch circuit. That is one of the problems with using the duplex outlets for making the in and out connections for the branch circuit wiring. Though I have seen the same thing happen with a slightly loose and or corroded joint where a cheap hard plastic wirenut was used.


Though none of the above has anything to do with the AC reversed polarity problem the OP is experiencing.

Jim.
hilde45 OP
As far as finding the outlet closest to the panel is a bit tricky, as the wire which feeds things disappears into the ceiling and I'm not sure where it goes first. I'm sure where the 3rd, 4th outlets are, but not the 1st, 2nd ones. If the problem was at the panel, that's at least clear. If it's not at the panel, then I suppose I can just *try* what might be outlet #1, first, and see what I find.

Turn off the breaker and start checking for everything that is Dead. Including ceiling lighting. For the wall receptacle outlets a 120V drop light works great.  You can move pretty fast from one outlet to the next.

Use a piece of masking tape on the cover plate showing you have checked the outlet/s. You might want to make a second pass to make sure you didn't miss one.

Jim

" So, our house is a mixture of old/DIY and new (renovation); the problem is with the old part of the house."


Hmm, that’s telling eh miller?
Thanks, all.
I ran out of time today, but I'm going to
(a) unplug all things on that chain
(b) measure again to see if the 4v are still there
(c) turn off the breaker and measure everything before (and more) again to see if there's leakage
(d) perhaps take off the breaker cover and see how that breaker is wired — WITHOUT touching anything.

I'll try to report back in case you all are still interested in interpreting.
This is really helpful.

Correction:

jea483,299 posts

03-22-2020
2:57pm


Also as I said previously.
1) VD, (Voltage Drop), on the neutral conductor due to the connected load on the branch circuit.

2) An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor.
4Vac would be pretty high in my opinion though.

"4Vac would be pretty high in my opinion though."

That statement was meant for #2 only.
( An induced voltage that is/may be created by the hot and neutral current carrying conductors onto the equipment grounding conductor. )
It does not apply to #1.

hilde45 OP286 posts

03-22-2020
2:35pm

So, our house is a mixture of old/DIY and new (renovation); the problem is with the old part of the house.
If you would have said the branch circuit wiring you were having the problem with is DIY, I would tell you to hire an electrician to find and fix the problem/s.



Is the wiring in the old part of the house original wiring? Any idea what year that part of the house was built?

Just a guess the branch circuit wiring you have been troubleshooting is 14 gauge. The breaker in the panel is a 15 amp.
Just a guess there is maybe 6 to 8 duplex receptacles on the circuit. At present you have not posted if there are any ceiling light fixtures on the circuit.

By chance do you know what type of wiring the branch is? Is any of it exposed where you can see it? Maybe a back side of an unfinished wall? Maybe in the room the electrical panel is located?
Examples of the type of the branch circuit wiring:
Romex?
Thin wall rigid (EMT) Conduit and wire?
BX? (Wire with an outer flexible interlocked steel armor).

"The 4 volts should be zero."
Rarely with a multi-meter on a circuit with things plugged in and turned on, especially with cheap meters. Usually there is enough noise to cause a multi-meter to read something, and to almargs point, add in voltage drops with loads. 4V seems excessive. 0V would be rare.
Guys, way to much time has been spent on this thread about the OP measuring a difference of potential, voltage, of 4 volts, from the neutral to the equipment ground contact on the receptacle outlet.
His biggest problem is reversed AC polarity he measured at the outlet. And as he has later posted the same reversed polarity he measured at other outlets on the same branch circuit.

As for the 4 volt the OP measured was it really 4Vac? Who knows.

I just checked a duplex receptacle that is fed by a 20 amp dedicated branch that is used to feed a treadmill. The branch circuit is #12/2 with ground Romex that is about 40ft from the electrical panel at best.

The test:
Multimeter, a Fluke 87. First test, meter set to AC volts. Default range auto scale. Reading,
power switch turned on treadmill only, standby state. Belt not running. Line voltage, 121.5Vac. Neutral to equipment ground, 9.4mv. (Meter allowed to settle down). Note, mv....
(Note Motor in treadmill is DC. That means the power supply is DC. Noise?)

I changed the range setting on the multimeter to 400Vac That is the closest range available above 122Vac.
Line voltage, 121.8Vac. Neutral to equipment ground contact, (after the meter settled down after about 10 sec or so), a steady 0.3Vac.

The above is for one finite test only. A different connected load, and type of load, no doubt would yield different results. No doubt a different, longer branch circuit with different connected loads would make a difference. I could go on and with different scenarios that would, could, make a difference in the neutral to equipment ground difference of potential, voltage.

What really matters? The conductivity, integrity (for a lack of a better word), of the equipment ground to be able to safely carry a ground fault current back to the source and hopefully cause the branch circuit breaker to trip open. (Note. In the event of a bolted ground fault event the instantaneous current could very well exceed 1000 amps.)


Jim
.
I would not open the panel if you dont have to. You've gotten a lot of good advice here. Like mentioned above, I would shut off the breaker to the circuit, then open up the closest receptacle to the panel that would be reversed polarity.  If you fix that one, then every other box will be fixed. Highly unlikely it is reversed inside the panel. 

2 tips. Be conscious of any switches outlets when testing, so there are no surprises.
When trying to find the first receptacle box, you can disconnect one pair of wires from the receptacle. THEN reapply power to find out if you're in the beginning or middle of the circuit. OR a more safe way is to test for continuity from one box to the next WITH THE POWER OFF. Then you'll know which is first. 
I also would not open a light fixture for starters. I say this only because of your experience.. It may very well be in a light fixture feeding the first receptacle box. So the first box may look correctly wired, but the connection from the fixture may have been reversed. This last scenario is my best guess.
Good luck
Yes, please update if you can. Curious...
Thank you
Jim: "Is the wiring in the old part of the house original wiring? Any idea what year that part of the house was built?"
Not likely. House built in 1910.
I don't know what else is on the circuit. I need to test.
Other questions will require inquiry, and I'm a novice, so may be inconclusive.

Cissado -- I will avoid opening the panel. I like your idea of trying to fix it with a receptacle.
I will watch for switches, and try the disconnect method.

Bottom line is that I'm curious up to a point. I am suspicious of the overall electrical job done in the older part of the house (DIY from previous owner). So, it won't take much to push this off onto a fully qualified electrician who will be working on other jobs (and perhaps installing a dedicated line).

The reason I'm curious now, as I think I mentioned, is that I'm trying out my audio gear and have been shoved to an inconvenient side of my room because of this polarity problem; so, a fix would be helpful in terms of audio set up.

I'll try to update soon. I have a stack of midterm exams to grade. (He says, posting on Audiogon anyway. ;-)

@ cissado

Good post except in the case of where the duplex receptacle device may have been used as a junction for the make up of neutral and Hot conductors coming in and going out of the outlet box.

We don’t know what type of wiring materials/methods were used for the branch circuit wiring.

What year NEC was in effect at the time? What were the AHJ electrical code standards/requirements back then for where he lives? Was conduit required in basements back then? Is there a chance the branch circuit is part of a multi wire branch circuit? What happens if he breaks the feed neutral at an outlet and the other circuit of the multi wire branch circuit has a connected load on it?

The OP is not an electrician. An electrician would know what to look for. Like another Hot circuit conductor passing through the box he is about to open a neutral. An open neutral on a multi wire branch circuit has killed many a electricians.

Jim


Post removed 
hilde45 OP288 posts

03-23-2020
11:44am



The reason I’m curious now, as I think I mentioned, is that I’m trying out my audio gear and have been shoved to an inconvenient side of my room because of this polarity problem; so, a fix would be helpful in terms of audio set up.
For this task only.

IF all you want to do is to correct the AC polarity at the outlet you want to plug in the power condition for your audio equipment. Nothing more at this time.....
If you want to do more than that I would suggest you hire an electrician. Better safe than sorry....



From one of my posts above:

Make 100% sure the breaker that feeds the outlet is turned off. Plug a lamp into the outlet. Turn the lamp on. The bulb lights. Go turn off the breaker. The light bulb is no longer lit. Use your mulimeter to verify the outlet is DEAD.

Carefully pull the duplex outlet from the wall box. HOPEFULLY there is only three wires connected to the outlet device.

If more than 3 wires connected to the outlet device,... stop..... Do not proceed.... Draw a picture on a piece of paper showing exactly how the device is now wired noting exactly how and where each colored black and white wires are connected on the outlet device. Make sure to note if the black and white wires are only connected to the side screw terminals. Or maybe also stabbed in the back into quick connect pressure terminals. **Look for any other color wire that may be passing through the outlet box.

Post back you findings.

Note, for the branch circuit wiring:
(Per NEC there shall be only one equipment grounding wire connected to the equipment ground terminal on the duplex receptacle outlet device. All equipment grounding conductors within the outlet box shall be joined/jointed together with a pigtail extended out for connection to the duplex receptacle device.) If the outlet box is metallic, made of steel, the box shall be grounded as well.

Jim.
Thanks, Jim. And I'm not doing anything without rereading these posts and triple checking things are dead. And if I'm even 10% uncertain, I'll just skip it!

But I'm learning a lot and so there's already been a payoff.
I ran out of time today, but I'm going to
(a) unplug all things on that chain
(b) measure again to see if the 4v are still there




Not really going the right way.  The voltage appears because you have a resistance on the neutral (bad connection or too thin a conductor) along with current (any other devices on it).

Lets say you use a perfectly good incandescent lamp, and you turn it on, and 4 V appears, off, it goes away.  The lamp is not bad.  The problem is the lamp is passing current (that's how these pesky electric devices work), and the resistance on the neutral is too high. Regardless of the device causing it, your problem is the wiring, not the device.

Best,


E

Hilde45, when you measured the 4 volts while the system was plugged in, were the components in the system turned on, or were they turned off or at least in standby? And as far as you know was anything else that is on the same branch turned on at the time?

If a lot of stuff was turned on at the time it increases the likelihood that the explanations cited by Erik and Jim apply. If not, it increases the likelihood that my hypothesis applies, namely that applying 120 volts to the AC neutral input of the component(s) resulted in excessive AC leakage to ground, mainly via their power transformers. Or, as heaudio123 alluded to, if significant current was being drawn by the components or other things the cause could have been a combination of both factors.

If my hypothesis was the main contributor, though, that issue should go away once the hot and neutral connections are reversed to what they should be.

Best regards,
-- Al