Possibel earthing issue?

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Need a little education, please… Now this may sound a little strange, but I and some other people appear to be able to feel a very small electrical current flowing in the metal casing etc of some electrical appliances, whereas others can not – and I wonder what it means.

This first started when I was a kid (a loooong time ago) and my uncle gave me an old military radio set, consisting of two big metal boxes (one a PSU, the other the actual radio) and a set of high impedance headphones. What I noticed was that, if I moved the sensitive skin on the inside of my wrist over the surface of the metal cases, I felt a strange (gentle) buzzing sensation. It wasn’t anything like a shock. I told a couple of my mates about it; they tried too, but couldn't feel anything, and marked me down provisionally as a loony who would probably get into trouble with drugs in later life. But recently I discovered that my cousin can feel it too.

So… the radio set is long gone, but occasionally, over the intervening 50-60 years, I’ve encountered the same sensation, in workplaces, people’s houses etc. I’ve always assumed it’s some kind of earthing problem, but perhaps not dangerous, as fuses aren’t blowing etc, but what do I know…

Anyway, I have recently discovered a similar phenomenon in my current house – I took the rubber cover off my mobile phone while it was charging, and felt the old familiar sensation through the metal casing.

I tested the sockets with a socket tester plug from Screwfix, and it reported all OK, but I’m aware life often isn't that simple. Can anybody comment please? Is my life in danger here? Is there any further testing a non-spark like me can do, if necessary?

Thanks :D
 
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It is a LACK of earthing that allows metal parts of the case to be become pseudo Live. Provided there is no damage to the item or damp in the item then the pseudo Live is not hazardous to a person.

The internal circuitry is NOT connected to tne metal of the case, in fact there are two layers of insulation between the electrics and the case, ( Double Insulated )

The pseudo Live is the result of capacitive coupling of voltage across the insulation from the electrics to the case. The capacitance is ( should be ) extremely small and hence very little current can flow from the case into a person. Enough current to stimulate a sensitive nerve ending but no where near enough current to create an electrical shock hazard.

There is an extremely slight risk that a person experiencing an unexpected pseudo Live may panic and create a non electrical hazard in their panic.
 
The pseudo Live is the result of capacitive coupling of voltage across the insulation from the electrics to the case.

What a wonderful explanation - I had no idea it was a recognised phenomenon!

You've cleared up a lifetime mystery :notworthy:

PS and I CAN spell "possible" - unfortunately my fingers can't :eek::eek::eek:
 
in fact there are two layers of insulation

There SHOULD be two layers of insulation and in most items rated as Double Insulated ther are two layers ( or one "re-inforced" layer ).

A few items from dubious suppliers may not fully adhere to the rules yet the supplier / manufacturer still claim that the item is Double Insulated.
 
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The internal circuitry is NOT connected to tne metal of the case, in fact there are two layers of insulation between the electrics and the case, ( Double Insulated )
There is the other class of equipment where there IS a connection between supply and case - common in TVs and other A?V equipment with two-wire mains leads.
Comes up fairly frequently on this forum. Explanation is that the device includes filtering components between both supply lines and the case. The end result is that the case is connected to the mid-point of a potential divider across the supply lines, and in the UK that means that there's a weak (due to the high impedance of the filtering components) supply driving the case to be at 120V AC :eek:

As Benard says, both this and the stray capacitance to a DI case can drive only a tiny current - enough to cause the buzzing sensation (I know exactly the feeling you mean, it's a strange sensation *) but not enough to be dangerous. I do wonder though about the situation where you have a pile of A/V gear, with their cases all connected together via the cables, as so 3, 4, ... times as much drive of this 120V AC.

* It took me a while to realise what it was, but I get it from my laptop (Macbook Pro) - depending on how it's powered and what it's connected to. Some adapters (IIRC the "duckhead) don't ground the ground pin of the power supply which is in turn connected to the filtering components; while others (IIRC the cabled alternatives) do. And if the computer is connected to something that's earthed, then that will earth the case and the "buzz" is gone.
It also depends on how well earthed I am - if I touch something earthed then it's a lot stronger, verging on painful. For example, recently I've been connecting up to the TV to watch recordings - if I touch the metal of the Displayport or HDMI plug (connected to the TV which is indirectly earthed via the MythTV server downstairs and the aerial cables) at the same time as my laptop then it's far more than just a slight tingling :censored:
 
What a wonderful explanation - I had no idea it was a recognised phenomenon!

Be aware that the tingle might not be due to the item you are touching, it could be the item you are touching is actually earthed and a 'something else' you are in contact with is, is actually the 'pseudo live'. You will feel the tingle on many items which are double insulated, yet have exterior metal parts, especially so if another part of your body is in contact with an earthed part. The tingle should only be apparent, when you make light point contact which such a metal object. The tingle should go when you take a firm grasp.

If in doubt - all items which are double insulated and therefore do not require to be earthed, should have a symbol of a square box inside a second square box. Its very unlikely your military radio set (88 set, 22 set ?) was classified and double insulated.
 
Interesting thread.
Yes, I too can feel this 'pseudo live' tingle. A recent example is a metal standard lamp, and this has reminded me of a question I may have asked a long time ago (but can't remember having answered).
Presumably, for me to feel this tingle, the metal lamp standard cannot be earthed and, of course, I'll have to have a look. Assuming it isn't earthed, would there be any danger in me connecting an earth wire to the metal part of the lamp?
 
Interesting thread.
Yes, I too can feel this 'pseudo live' tingle. A recent example is a metal standard lamp, and this has reminded me of a question I may have asked a long time ago (but can't remember having answered).
Presumably, for me to feel this tingle, the metal lamp standard cannot be earthed and, of course, I'll have to have a look. Assuming it isn't earthed, would there be any danger in me connecting an earth wire to the metal part of the lamp?

If there is exposed metal which not earthed, then look for the double - square inside a square symbol, if it lacks that then certainly it needs to be properly earthed.

Old metal table and standard lamps were commonly not earthed, just wired in to core flex. Back in those days, many sockets were two pin, live and neutral. It was less of a danger then, because there wasn't so much earthed metal about in homes. Now we have radiators, pipes and fixed metal baths etc., all connected to earth.
 
If there is exposed metal which not earthed, then look for the double - square inside a square symbol, if it lacks that then certainly it needs to be properly earthed.

Old metal table and standard lamps were commonly not earthed, just wired in to core flex. Back in those days, many sockets were two pin, live and neutral. It was less of a danger then, because there wasn't so much earthed metal about in homes. Now we have radiators, pipes and fixed metal baths etc., all connected to earth.
Thanks for that quick response.
Yes, I'll have to look for a double square symbol; I hadn't noticed one before, though. I must also check, as I said, for an earth wire.
 
Assuming it isn't earthed, would there be any danger in me connecting an earth wire to the metal part of the lamp?

The logical answer is that there is no harm in earthing the metal work.

Some will claim it will increase the risk of a serious electrical shock if a person is holding the earthed item and at the same time is touching a Live item. The risk is that a faulty item ( A ) has Live exposed metal parts. By itself item (A) poses a very small risk of serious electric shock. It can be touched without get a signifcant shock from it as long as no part of the person is touching anything else that is electrically conductive. (*)

A serious electrical shock require two points of contact, one to Live and the other to something other than Live ( Earth, Neutral or another phase ) and both these points of contact need to be able to carry enough current in, through and out of the body to cause a reaction in the person.

If there are no Earthed items close to faulty item (A) then contact with the necessary two current carrying points of contact is very unlikely to happen.

Hence changing an un-earthed item to become an Earthed item does increase the risk of a person having access to two points of contact, faulty item (A) and the newly earthed item and thus increases the risk of significant electrical shock.

(*) Do NOT test this.
 
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There is the other class of equipment where there IS a connection between supply and case - common in TVs and other A?V equipment with two-wire mains leads. .... Comes up fairly frequently on this forum. Explanation is that the device includes filtering components between both supply lines and the case. The end result is that the case is connected to the mid-point of a potential divider across the supply lines ...
Is that actually true?

When such equipment has a "3-wire mains lead" it is, indeed, common to have filter capacitors between L & E and between N & E, resulting in the situation you describe. However, I've never noticed filter capacitors being connected to the unearthed case of a Class II item and, at first thought, I can think of no reason why that would be done. I'm not even convinced that it would be 'allowed'.

Kind Regards, John
 
The logical answer is that there is no harm in earthing the metal work. .... Some will claim it will increase the risk of a serious electrical shock if a person is holding the earthed item and at the same time is touching a Live item.
You presumably count yourself amongst those "some", since you go on to conclude (correctly) ....
.... Hence changing an un-earthed item to become an Earthed item does increase the risk of a person having access to two points of contact, faulty item (A) and the newly earthed item and thus increases the risk of significant electrical shock.
You do go on to indicate that the increased risk is very small, when you write:
If there are no Earthed items close to faulty item (A) then contact with the necessary two current carrying points of contact is very unlikely to happen....
... but the fact that a risk arises from a scenario which is "very unlikely" doesn't usually stop you worrying about it!

Perhaps more to the point, is there not an inconsistency in what is being suggested? As you say, there is an increased risk of a serious electrical shock if an item which does not need to be earthed is, nevertheless ('unnecessarily'), earthed, but that risk only arises in a scenario which "very unlikely". Is it not equally "very unlikely" that a scenario will arise in which not earthing something which should be earthed (i.e. the exposed-c-ps of a Class I item)? In both cases, for their to be a serious risk, there needs to be two points of contact, one of which is earthed and the other of which be comes live because of a fault - and I'm not sure that that is necessarily all that more likely in the latter case.

Kind Regards, John
 
However, I've never noticed filter capacitors being connected to the unearthed case of a Class II item and, at first thought, I can think of no reason why that would be done. I'm not even convinced that it would be 'allowed'.

Kind Regards, John
I would agree with your concern since failure of either of the 'filter' capacitors could raise the casing to full mains potential - the worst case scenario being a short on the live-side capacitor.
 
I would agree with your concern since failure of either of the 'filter' capacitors could raise the casing to full mains potential - the worst case scenario being a short on the live-side capacitor.
Exactly - which is the main reason why I said that I'm not convinced that it would even be 'allowed'.

As I said, I've certainly never seen, nor heard of, it ever being done. One does not expect anything to be (electrically) connected go the unearthed casing of a Class II item, let alone something which, under fault conditions could result in that casing being connected to a live supply.

Kind Regards, John
 
As I said, I've certainly never seen, nor heard of, it ever being done. One does not expect anything to be (electrically) connected go the unearthed casing of a Class II item,
Surely that is an oxymoron.

Even if it were alowed, it could hardly be described as Class II. I.e with no insulation.[/QUOTE]
 

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