For some months, I'm renting an apartment in the Canary Islands. It looks like the plugs are not grounded. For example, when I connect my laptop, a ThinkPad T420si, then I feel an unpleasant sensation on my bare legs when connected to mains (220V/50Hz). A similar sensation I get when touching certain parts, incl. plastic parts (!), of my smartphone when connected to the laptop. Contrary to what I wrote before: When connected to the USB charger, I do not get that sensation when touching the smartphone.

My guess is that the outlets are not properly grounded. While I assume there is no risk for my health, I am a bit worried about my electronic devices. Also, I may want to do some electronics soldering, and I don't like the idea of the soldering iron's tip possibly being on a different potential than ground.

What options do I have to remedy the problem? An isolating transformer?

Update as of 2014-10-15 WEST

After removing the Schuko (fype F) multiplier, and upon close inspection of the outlet, I realized that the center hole is not a screw hole. It is ground, i.e. this outlet is of type L. So I bought an adapter, and yesterday the problem was gone:

Photo of adapter type L to type F


But wait, today the problem is back, and in the entire apartment! For the first time, I felt a potential when touching the washing machine in the bathroom, and this one is connected with a Schuko plug to a Schuko outlet:

Photo of washing machine plug type F in outlet of the same type

Something is wrong here. Probably unrelated: Some days ago there was a power outage, I think affecting several houses, i.e. not just the one I'm living in.

  • 1
    Correct me if I'm wrong, but a laptop's brick power supply and a cell phone power supply each already have an isolation transformer. They are Class II.
    – Nick Alexeev
    Oct 12, 2014 at 17:18
  • 1
    @NickAlexeev But, if they are equipped with a ground-pin that ground may be coupled to the negative terminal with a high resistor and/or a capacitor. If the ground then is wired, but never anywhere connected to ground, the ground pin may inductively/capacitively be swinging anywhere between 10VAC and 230VAC with enough "zapp" to tingle.
    – Asmyldof
    Oct 12, 2014 at 17:29
  • Why the downvote? Are questions concerning mains OT?
    – feklee
    Oct 12, 2014 at 17:39
  • 2
    @Ariser If the O.P. wants to fix the wiring of his apartment in the Canary Islands, then this question belongs on DIY.SE (home improvement stack).
    – Nick Alexeev
    Oct 12, 2014 at 19:15
  • 1
    Please have a look at my recently updated answer. Your health may be at risk under certain circumstances.
    – Ariser
    Oct 17, 2014 at 11:13

2 Answers 2


This is not about grounding, or perhaps it is...

Lets start with your connectors: Do you have AC-connectors at your devices with or without grounding pin? Laptop psu may have a protective earth connection, a phone charger won't have one. I've never seen a phone charger with protective earth connection.

Both PSUs are doubly insulated, I'm pretty sure, which means primary side is galvanically separated from secondary side, which includes everything which can be touched with bare hands.

How does this sensation of 50 Hz AC come over to touchable parts? There's something calle Y-Capacitor between primary and secondary side in these PSUs. It is used to provides a stable potential for the regulating circuitry of the PSU, i.e. it prevents the secondary side from "floating". It can be described by two small capacitors in series between neutral lead and live lead on primary side with the middle node connected to the ground of the secondary side. Hence, on a 230V system, the secondary side gets a level of 115 V AC. The capacitor is designed to permit a maximum current of 0,35 mA to flow, if shorted to ground. This is a current you can sense, but which cannot harm you or your equipment.

If something with earthing in your mansion was wrong, it would not change this effect in my opinion.

In the rare case, your PSUs really have a protective earth connector you should not be able to sense that voltage as it was conducted away. In this rare case you should get an electrician soon, because if you touch your oven or washing machine there is no such limiting capacitor to protect you in case of an failure.

I have a different theory why you feel somthing you do not know at home. On canary islands it is rather warm and carpets are rare while most homes have tiled floor. If you live somewhere cold the rest of the year you probably have carpets or wooden floor which reduce capacitive coupling by orders of magnitude. You just may not feel the phenomenon while it is there, too.


Relating to your updates: Now you do have a problem. When you feel a tickling sensation when touching devices like a washing machine there is one possible conclusion: the potential of protective earth connected with the housing of your devices differs from the potential of your house. Which can mean different things.

  • You have only 2-wire conduits in your house. The neutral and protective earth in your wall outlets are connected to one common wire (usually blue in EU). Some connections in your house have too high ohmic resistance. When under heavy load, voltage on N and PE rises, hence you can feel the influenced voltage.
  • Protective Earth is somewhere broken, effectively. This is really bad, as all Class 1 equipment relies on working PE and a short to housing, which especially water bearing devices are prone to, will put the full voltage to touchable parts of the defective devices.
  • And if PE is interrupted at the equipotential bus bar it gets even worse. Not only a faulty potential from one defective device will propagate through your complete building and be present on every Schuko (PE contact), but will also be induced by assymetric load in the 3-phase-network between the next transformer station and your house. Which means, even if all devices in your house are depowered properly, PE-conductors may conduct harmful voltages.

For the last two options, your life is at risk. You should get an electrician to prove me wrong. The first possibility can be verified by opening a wall outlet (of course after opening the circuit breaker, securing it against reconnecting, verifying all pins in the outlet are deenergised and so on). If there are two wires only and one of them connects to N and PE you have a “bootleg ground”, which renders even ground fault interruptors partially useless.

  • Good point. Did not consider. Will leave my answer in case of ground problems anyway :-) +1
    – Asmyldof
    Oct 12, 2014 at 17:47
  • 1
    I experienced an identical issue on a 220V/50Hz system in a different country. In that scenario, I experienced the "tingly" sensation when touching the metal chassis of a MacBook Pro. I did some sleuthing and found that it only occurred on one particular outlet. With the same floor and footwear, even standing in the same place, connecting to any other outlet did not exhibit those symptoms. The problem outlet was a surface-mounted extension outlet that had three prongs, even though it suspiciously had only 2 wires leading back to the non-tingle-inducing mains outlet it was connected to...
    – Scott Dudley
    Oct 13, 2014 at 0:23
  • Apple devices tend to have a functional earth node which connects to protective earth when connected to a properly grounded wall outlet. Grounding of Apple PSUs is not mandatory, as the 3 wire cord can easily be replaced by 2 wire cords in Europe. But functional earthing brings this unpleasant leakage current directly down to the wall outlet, without bothering you. Aside from that a three-prong wall outlet without proper protective earthing is a real hazard and must be fixed ASAP.
    – Ariser
    Oct 13, 2014 at 16:19
  • Sorry, I initially provided wrong information. My question is now updated: The problem only appears with the laptop, which does have an power connector with grounding pin (Mickey Mouse cord). The phone charger does not have a grounding pin, and the problem does not exist. When I connect the phone by USB cable to the laptop, however, then I get that unpleasant sensation when touching.
    – feklee
    Oct 13, 2014 at 21:00
  • Thanks a lot for the update! At the moment the problem is not there. Could be that it was fixed today: There was some construction work, and also there was a strong smell in the air that I know from burnt electronics. Some days ago, I saw workers with cables, though I think that was telecom, looked like fiber.
    – feklee
    Oct 17, 2014 at 18:45

Steps to go through:

  1. Turn off the power to an outlet that is causing you problems. (Fusebox/main switch)
  2. Check the exterior of the outlet for presence of a metal grounding element/grounding pin/whatever you have over there.
  3. Open the outlet, check to see if there's proper wiring: all three pins connected.
  4. Close the outlet.

If the answer in 3 was: yup, all's well, next:

  1. Connect a multimeter to the ground of one outlet, connect the other side to another outlet somewhere else in a wall (not the same box, of course).
  2. Set the multimeter to "resistance" or "continuity" (the setting that beeps) and verify that the resistance is very low. (very very).

If the answer to that is: yup, low resistance:

  1. Verify that the power to the outlet is still safely turned off.
  2. Set the multimeter to voltage AC (high, at least 250VAC should be possible).
  3. Connect one terminal to Groung, the other to one outlet power wire (phase or neutral)
  4. Turn on the power to the outlet.
  5. Check the multimeter without touching. Measurement One
  6. Turn off the power to the outlet again
  7. Get the terminal from the power carrying wire and put it in the other, leaving the other terminal connected to ground.
  8. Turn on the power again.
  9. Check the multimeter without touching. Measurement Two.
  10. Turn off power.
  11. Remove the multimeter from the outlet.
  12. Turn on power.

Now, if one measurement says "230VAC" or close to it and the other says "0VAC" or something very close (no more than 1 or 2VAC), it's very likely the power ground is properly connected. It's no guarantee, but without being there myself I'm not getting any immediate other inspiration to do further verification.

If any of the earlier steps failed, obviously something is not right.

  • 1
    I would just like to add that a multimeter with the correct category MUST always be used. Do not go sticking a $3 multimeter in a plug socket!
    – George
    Oct 12, 2014 at 19:32
  • 1
    If there's an RCD, you'll probably trip it while measuring like this.
    – Bob
    Oct 12, 2014 at 22:15
  • @Bob Only if your RCD triggers at 0.23mA or less.
    – Asmyldof
    Oct 12, 2014 at 23:40
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    @George The key there is the "not touch" part. If I'm using my fluke I'll be measuring live running 380V, but a cheap toy can do these measurements no problem. 1. It will arc if it's really bad (it isn't) -> fuse cuts off. 2. It'll stray out -> You're not touching it with live power.
    – Asmyldof
    Oct 12, 2014 at 23:42
  • I have a problem with step #3. He suspects serious miswiring, I wouldn't dream of opening an outlet without first using a meter on it--or much easier: amazon.com/GE-3-Wire-Receptacle-Tester-50542/dp/B002LZTKIA Oct 13, 2014 at 1:44

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