Weird electric shock on laptop screen back case

Thread Starter

vincentbx715

Joined Aug 7, 2020
6
Hello guys!
I am experiencing a weird situation with my laptop.
I am using a newly bought Automatic Voltage Regulator rated for 1000 watts (Panther Brand with time delay).
I just noticed that when the I keep the AVR turned off but connected to the main electric wall socket, and then touch the edges of my laptop screen which is metal, I get mild electric shocks.
This does not happen when:
1. I disconnect the AVR from the wall socket
2. The AVR is completely turned on
3. The laptop adapter is disconnected from the laptop
4. Using another AVR and performing same steps to try reproducing the issue
5. If I wear rubber slippers and my feet does not touch the floor

I find it weird because the AVR seem to function fine but I get shocked only when it is plugged in to a wall socket, while it is turned off.
I suspected first that my laptop might have the issue but as stated above, it does not happen on the other AVR I have.
I was hoping someone here might know what exactly is going on as I just cannot figure it out myself.

Thanks in advance!
 

ScottWang

Joined Aug 23, 2012
6,933
If you are using AC110V and two pins power plug then you could try to change the direction of the power plug. (It means that you could exchange two pins of power plug when you plug into the wall socket)
 

Thread Starter

vincentbx715

Joined Aug 7, 2020
6
By the way, I tried that just now and it actually worked. Reversing the two pin from the AVR to the wall socket prevented the electric shocks. However, plugging it again in the other way, the electric shocks occur again.
Do you think there is an issue with the AVR or my laptop adapter in this case? Note that with both tests the AVR is turned off.
 

ScottWang

Joined Aug 23, 2012
6,933
Do you think there is an issue with the AVR or my laptop adapter in this case? Note that with both tests the AVR is turned off
That is a Grounding issue, rewiring the power line in your house could be a big engineering, so how to keep yourself safe is that you could try to build a safety environment, you could put some wooden or plastic stuff to where you working on, make your body isolated from the Ground, because when you touch the edges of laptop screen, the metal will transfering the leakage current to you and Ground, or you could wear the plastic slippers when you use the computer and AVR.

I'm too lazy, so normally that I only reversed the power plug.
 

Thread Starter

vincentbx715

Joined Aug 7, 2020
6
That is a Grounding issue, rewiring the power line in your house could be a big engineering, so how to keep yourself safe is that you could try to build a safety environment, you could put some wooden or plastic stuff to where you working on, make your body isolated from the Ground, because when you touch the edges of laptop screen, the metal will transfering the leakage current to you and Ground, or you could wear the plastic slippers when you use the computer and AVR.

I'm too lazy, so normally that I only reversed the power plug.
Thanks for your response!
So this does not have anything to do with the AVR then?
 

KeithWalker

Joined Jul 10, 2017
1,216
It appears that your house wiring is faulty with the phase and neutral wires reversed. It may be only that outlet or maybe more. This could be very dangerous. You can get a simple, inexpensive outlet tester from most hardware stores that will indicate wiring problems. When I moved into my current home,I heard that the previous owner acclaimed himself to be a handyman so I got a tester and checked all the outlets. More than half of them were incorrectly wired with reversed phases and some with no ground connection. It's a simple job to correct the wiring as long as you disconnect the power first at the breaker, and it could avoid some potential nasty shocks.
Regards,
Keith
 

Thread Starter

vincentbx715

Joined Aug 7, 2020
6
It appears that your house wiring is faulty with the phase and neutral wires reversed. It may be only that outlet or maybe more. This could be very dangerous. You can get a simple, inexpensive outlet tester from most hardware stores that will indicate wiring problems. When I moved into my current home,I heard that the previous owner acclaimed himself to be a handyman so I got a tester and checked all the outlets. More than half of them were incorrectly wired with reversed phases and some with no ground connection. It's a simple job to correct the wiring as long as you disconnect the power first at the breaker, and it could avoid some potential nasty shocks.
Regards,
Keith
Hi Keith,

Thanks for your reply.
For now I take it that my AVR is not faulty, so I won't go returning it (I would not want to claim warranty on a working item).
I will try to look into this, though I am not very knowledgeable on these things, we may just hire someone to check it.
 

KeithWalker

Joined Jul 10, 2017
1,216
Hi Keith,

Thanks for your reply.
For now I take it that my AVR is not faulty, so I won't go returning it (I would not want to claim warranty on a working item).
I will try to look into this, though I am not very knowledgeable on these things, we may just hire someone to check it.
Before you spend money on an "expert" you should get yourself a receptacle tester, something like this. They are around $10.00 or less. You just plug it in and read the results. Then you can tell your expert exactly what you want done on which outlets.
Tester.jpg
 

Hymie

Joined Mar 30, 2018
859
I would disagree with the analysis offered so far, I do not believe that the OP has an issue with their house wiring.

The PSU only has connection to Live and Neutral (there is no Earth connection); in only one orientation/connection polarity the OP experiences slight shocks from equipment plugged into the PSU output.

Based on the above, the most likely scenario is that there is some substandard insulation/component connected between one of the input poles and the PSU output. This might be due to a fault or the incorrect use of a safety rated capacitor. With the substandard insulation/component between the Live and PSU output, shocks occur; but when there is substandard insulation/component between the Neutral and PSU output, no shocks occur.

Either way, I would stop using the PSU and obtain a genuine replacement.
 

Tonyr1084

Joined Sep 24, 2015
5,039
Hi Keith,

Thanks for your reply.
For now I take it that my AVR is not faulty, so I won't go returning it (I would not want to claim warranty on a working item).
I will try to look into this, though I am not very knowledgeable on these things, we may just hire someone to check it.
I would say "Finish testing." You've tried another AVR (are we talking about an Uninteruptable Power Supply?). You've tried swapping the connection somewhere, either at the plug or at the AVR. But you haven't tried reversing the connection with the other AVR, the one you said is working. If you reverse that one and you again get a shock then either it's a design flaw in the AVR or there's something up with the wiring.

Me? I'd go ahead and test the outlets to make sure they're wired correctly. I ran into a nasty situation when I plugged a computer into one outlet and a printer into another - all on the same breaker. When I plugged the printer into the computer that's when I saw the light. Lots of it. And got a good shocking as well. The previous owner installed three pin outlets everywhere because some modern equipment can't be plugged into two pin outlets. And to make the wiring seem proper he (or she) grounded the ground pin to the neutral. That's not to code. And in the basement, behind the acoustic ceiling tiles (ugly crap they put up) was where there was a wire break. When I found that - black was wired to white and white to black. One outlet in that room was powered correctly while the rest were all reversed. With the neutrals tied to ground, my computer, when plugged into that one outlet was actually "Case Hot" instead of Case Ground like it should have been. The printer was properly wired. When the interface cable, which is grounded came in contact with the metal housing of the computer that was when there was the big flash of light and the shock.

So I'd recommend testing your outlets just for the sake of safety and piece of mind knowing your wiring is not faulty. Just because a different AVR didn't cause a shock doesn't mean everything is OK with the wiring. Since you had to reverse the wires, which should never be the case, something is wrong; and it's well worth "Fully" diagnosing the problem.

Many years ago I brought home a salvaged power supply from work. When I plugged it into a three pin outlet the PS blew the fuse. When I looked into it - my landlord had done a bunch of rewiring himself. To him AC is AC. Not polarized. But when my PS blew the fuse I started checking which wire was hot. Sure enough - hot and neutral were reversed. I could have rewired the PS to accept that condition, but that wasn't the problem. So fully diagnose the problem before someone gets hurt.
 

KeithWalker

Joined Jul 10, 2017
1,216
I agree with Tony. It does sound as though you have faulty house wiring. It's so easy to check it with an inexpensive outlet tester and the life you may save could be yours!
If you really can't afford an outlet tester,use your multimeter Make sure you are using the insulated probes that came with the meter. Set the function to ACV. and measure the voltage between neutral and ground on the outlet. If you get supply voltage indicated, the phases are switched. If it's OK, measure between phase (hot) and ground. If you don't get a high reading, the ground is not connected.
Keith
 

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Thread Starter

vincentbx715

Joined Aug 7, 2020
6
I agree with Tony. It does sound as though you have faulty house wiring. It's so easy to check it with an inexpensive outlet tester and the life you may save could be yours!
If you really can't afford an outlet tester,use your multimeter Make sure you are using the insulated probes that came with the meter. Set the function to ACV. and measure the voltage between neutral and ground on the outlet. If you get supply voltage indicated, the phases are switched. If it's OK, measure between phase (hot) and ground. If you don't get a high reading, the ground is not connected.
Keith
Hi Keith and Tony,
I currently don't have equipment to do testing myself and it is quite difficult in out area to get a hold of one, especially during this time as we have strict quarantine rules.
But I will try to get a tester if I can or at least ask a professional to do some checking if we find someone like that near our home.
Also, just to give a bit more info, our home's electric sockets are dual flat pins only, no ground connection is present.
 

Tonyr1084

Joined Sep 24, 2015
5,039
You CAN make your own tester out of some scrap pieces. A lightbulb and socket. Wire just the two wires to the bulb. If you have a soldering iron you can tin the ends of the wires so you can probe inside the socket. Like Keith said, test between neutral and ground. If the light bulb lights up - you have a problem. Test between hot and ground. If the bulb doesn't light up - you have a problem. Obviously between hot and neutral should work. If it doesn't - you have a problem.

You won't be able to determine the voltage, but you'll know whether things are functioning fairly normal - or absolutely incorrect. Don't use an LED type bulb, use an incandescent type. LED's and CFL's can still light on partial voltages if they're high enough and there's enough current available.

When I replaced my swamp cooler on the roof there was a mish-mash of wiring up there. Someone obviously didn't know what they were doing. In order to determine which lines had proper voltage AND current I had to use a lamp. A meter could still read stray voltages on near-by lines; which is one problem I was having. In the end I decided to just pull everything out and start over. Get it done right.

When moving the outlet for the refrigerator I kept getting signals even though I believed I had the right breaker off. And I DID have the right breaker off. But I still got indications of voltage present. In that case I just plugged a loud vacuum cleaner in and switched it on. Then back to the breaker box to toggle the breaker. Sure enough - I had the right breaker. But still nervous that I was still reading 110VAC on the line I decided to just switch everything off. Moved the outlet and turned everything back on.

Lectrisitee is nuttin' to muss wit'. I gots plenty shockin's and dare ain't nuttin wrong wif I. Though I've survived numerous shocking's of 120 VAC; there's that one last time you get a shock. I said "One Last Time". After that you go the way of the Pilsbury Dough Boy. He passed away. Services were held on a Saturday at 350 for 20 minutes.
 

MaxHeadRoom

Joined Jul 18, 2013
21,403
I don't quite agree with the house wiring being the problem, It sounds to me as though there is leakage in the AVR, i.e. not 100% isolated, if using a 2 pin plug, it s most likely not a polarized version, if the sockets are wired correctly with the wide side of the outlet on neutral, if should not happen, but the error appears to me to be in the SMPS or whatever the supply is.
Even if the socket is wired backwards, a shock should not occur.
Max.
 

Tonyr1084

Joined Sep 24, 2015
5,039
I don't quite agree with the house wiring being the problem, It sounds to me as though there is leakage in the AVR, i.e. not 100% isolated, if using a 2 pin plug, it s most likely not a polarized version, if the sockets are wired correctly with the wide side of the outlet on neutral, if should not happen, but the error appears to me to be in the SMPS or whatever the supply is.
Even if the socket is wired backwards, a shock should not occur.
Max.
Meant to say that myself but got caught up in testing the house wiring. But yeah, it seems more likely the supply (AVR) may be at fault. Nevertheless, testing everything will reveal factually where the issue lies.
 

MisterBill2

Joined Jan 23, 2018
6,998
This is confusing indeed. The TS has a laptop computer that uses an external power supply that normally would connect to the mains power. My first guess is that this arrangement worked previously plugged into the same outlet. Next, for a reason not explained at all, the TS obtained an Automatic Voltage Regulator device and connected it between the outlet and the external computer power supply.
Since all of the external power supplies that I have ever come across are regulated I am wondering why an external regulator package was added in between the original supply and the mains connection. That reason is hard for me to imagine.
Is there some connection to the AC mains passing through the computer power supply? Is the input side ground terminal on the power supply plug somehow connected to the computer connection? AND, if the AVR device has only a two wire mains connection, but three wire outlets, what is connected to the ground pin of the AVR outlets inside of it?
So there is a whole string of missing information here.
 
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