Eathing, Shock from AV device, Shock from laptop

Hello everyone,

We have been discussing all the issues from the operator point of view! Some of us might have noticed the small shock when touching the rear panel, or even when we touch the appliance itself... yes, dont simply blame it on earthing. Thats what everybody says, but check this senario.

I recently purchased a LG LED LCD TV, 22''. It has got a power adaptor, like what a laptop has. Basically, it works on dc. From day one, I noticed a slight shock when ever I touched the rear connection panels (AV, component..etc). I reported this to LG, for which they asked me check the earthing. Well, first thing I need to know is,..
1. Since an adaptor is used, and the output terminal consists of two terminals only, positive and earth, how is it connected with the TV?

2. Same is the case with laptop adaptors, all it needs is dc supply then what is the need of the third big pin/earthing?. Afterall the laptop is not connected to the ground. So what is the internal connection like?

Then I did something which amazed me, I took a tester, and touched the end of the terminal, which is plugged into the laptop, and it lighted up!! Same was the case with the TV's adaptor. But note that the current was not of lethal amount. When I touched, I didnt feel any shovk, but a small tinking sensation!!

Now I was very sure there was no issue with the adaptors, but there was something wrong with the house wiring. Next, I removed the earth pin, and tried, ans still the tester lighted up!! What could be wrong?

I moved out to a new apartment and noticed that everything is working fine here. I dont get that small shock on touching the appliance, also the tester doesnt light up when touching the dc feed end. I removed the earth pin and repeated the above steps, and here also it was fine, no shock, no light on tester!!!

So the issue was indeed related to wiring in my previous apartment. Has anyone got any clues? Electrical Engineers????!!!

Hi,

See there can many reasons for the same,but for one I say you should get the earthing tested ! If thats not it then try the following !

1.Try and reverse the Pin (if its a two pin plug) the thing here is most of the new gen adapters work on SMPS where the entire circuit is grounded,so if you plug the pin reversely the Phase (+) will flow to the ground instead of Neutral and create a small leakage enough give a mild shock ! The same applies to three pin where Live/Phase is reversed !

2. Check and make sure the other devices like STB or such where the cable comes from outside is not touching any wires or passing over a high tension wires.

3. Faulty Earthing can also cause this,as in the earthing is partially weak due to the age of the original installation !

4. Finally ask someone else to touch the same points to see if they get the shock (Am sorry but this is important ) The reason for this is, One's body resistance differs from the others,this is also the cause of the mild shocks and not necessarily related to the Power !

Please check and revert back with the status for more !!

Regards.

Hi,

Thank you for the quick response.

1. Revesing the connection.
It did not had any effect, I could feel the mild shock, in both the ways
I removed the earth pin, and the effect was same.

2. No insulation damage of the live wire, so as get a shock due
to insulation failure.

3.Earthing!! What is the proper way to test it? I tried these steps..
a. Connecting a 2 pin plug, in such a way that one of the pin goes to the
live, and other to earth(not neutral). The device(mobile charger) was
working fine.
What I need to know here is since earthing is for safety, incase there is any
insulation failure, how come I received mild shock from the laptop adaptor,
when I checked it with earth pin removed? And, it was not just one adaptor, my friends laptop too had this problem there. So it was indeed some issue with the wiring there, either earth fault or neutral fault??

As mentioned in my previos blog, I moved into a new apartment, and theres no shock here, when I reversed the connection, even when I removed the earth pin!! Ground too is fine as I checked it as I mentioned above!!

So, it was wiring fault where I stayed previously, but why?? Even with the earth pin removed it gives me no shock here, in my new house, but it would give me a shock in my previos house no matter the earth pin is there or not!

Hi,

Well after reading your post seems to me that the problem is from the weak building,why you ask ? if its a very old building then for junctions and such they used to use metal parts which will conduct even if they don't necessarily come in direct contact with the bares wires,the reason for this is again the grounding !

The grounding although seem fine cannot be just tested by a small charger,you need either proper earth tester or a multimeter or the latest small unit from MX which does the job of testing the earth !

Now if you consider this, You have a house with old wiring done in above said manner and the earth is a wee bit weak or even if its perfect the building itself being old will have small amount of electricity passing through the walls ( YES walls, you may get a mild shock if you touch some part of the wall too ) !!

Again I would like emphasis on the fact that your body resistance player a major role too, you don't directly relate it to the earth pin present or not for that ! you are standing on the ground which is a surface which leads to the master earth of your house or the has some leakage (like said above) so you are bare footed and are standing on the ground and touch a electrical appliance ! With respect to the appliance you are the nearest ground to it hence the excess charge escapes through you to the ground !

You say the adapter has only two pins and how can that still give you a mild shock, same for the above said reasons, also like I said in my post the new gen adapter are based on SMPS technology and no matter what you do the ground is always present (as in the electrical common point in the design ) so if there is a small leakage then the ground which is -Ve pin in the wire that you connect to the laptop has that leakage and will transfer that leakage through you to the ground the moment you touch it !

So I think I made my point here ??? if not try testing this way, wear a rubber slipper or stand on a wooden plank and touch, I can tell you not get any shocks !! Why ? either of the material mentioned above can conduct electricity hence the transfer of the excess or leakage to ground is not possible !

Hope this helps !

Regards.