When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Daniele

On 25/08/09 09:16, D.M. Procida wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Similar on my laptop, I notice it more when I'm in contact with earthed
metal (e.g. I've rested the laptop on a short 19" rack and bridge
between the rack and laptop with my forearm/wrist).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Could it simply be due to the different rings being in different
locations and having different floor coverings, therefore *you* are
better earthed (or insulated) when using it on one ring compared to the
other?

On Tue, 25 Aug 2009 09:16:32 +0100, D.M. Procida wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

Have you checked only with one socket (oe double socket if that's the case)
on each ring?

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Nothing springs immediately to mind other than to ask, have you checked the
socket is wired correctly?

--
The Wanderer

That no one understands doesn't make you an artist.

On 25 Aug, 09:16, (D.M.
Procida) wrote:
When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Daniele

This is normal for metal-cased laptops, as they are not double-
insulated. The tingle you feel is leakage current through the power
supply capacitors. This should go away if you use the full mains lead
instead of the plastic 3-pin adaptor, as the former is has a proper
earth connection to the supply).

If you measure the potential of the case with respect to earth, using
a high-impedance multimeter, you'll see that your laptop is at ~120V.
This is not a fault.

Dave

In article
,
D.M. Procida wrote:
When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

There are commonly high value resistors between what is effectively mains
and the casing of such devices for RFI suppression purposes. And you can
feel a slight tingle from these under certain circumstances. Perfectly
safe, though.

I can't think why one ring over another would make any difference - more
likely the local conditions in the room. Although you could check there
isn't a neutral line reversal on the socket using one of those plug in
testers.

If it really annoys no reason you couldn't earth the casing.

--
*There's two theories to arguing with a woman. Neither one works *

Dave Plowman London SW
To e-mail, change noise into sound.

On 25/08/2009 09:16, in article
, "D.M.
Procida" wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

I get this whenever I
- use my MBP on the train and
- plug the power adaptor into the in-seat (table) power and
- rest one arm on the MBP and the other on the (presumably metal, earthed)
arm-rest.

It can actually be quite painful - like a stinging more than a tingling.
This might be because it comes through the underside of my fore-arm which is
more sensitive than fingers or the back of the arm.

I've meant to try using the long power lead with the power supply, instead
of just the stubby plug thing (which doesn't have an earth). I haven't
because I can't find it...

I've also not wanted to use a multimeter on it on the train because of the
strange looks and/or accusations of terrorism which may ensue.

Piers Finlayson wrote:



I've also not wanted to use a multimeter on it on the train because of the
strange looks and/or accusations of terrorism which may ensue.


Its statements like that , that make you know that Al Qaeda has in fact
succeeded.

In article ,
Piers Finlayson wrote:
I get this whenever I - use my MBP on the train and - plug the power
adaptor into the in-seat (table) power and - rest one arm on the MBP
and the other on the (presumably metal, earthed) arm-rest.

It can actually be quite painful - like a stinging more than a tingling.
This might be because it comes through the underside of my fore-arm
which is more sensitive than fingers or the back of the arm.

I've meant to try using the long power lead with the power supply,
instead of just the stubby plug thing (which doesn't have an earth). I
haven't because I can't find it...

I've also not wanted to use a multimeter on it on the train because of
the strange looks and/or accusations of terrorism which may ensue.

You could use a neon screwdriver. Will light up nicely. But neither that
or a DVM tells you much since they draw virtually no current. And you
already know there are volts present. ;-)

--
*The statement below is true.

Dave Plowman London SW
To e-mail, change noise into sound.

On Tue, 25 Aug 2009 09:16:32 +0100,
(D.M. Procida) wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Daniele

If you put a voltmeter across the earth and neutral connections you
may find a fairly high voltage exists between them.

One of my sockets has 110 volts across those wires. It varies on other
sockets down to a few volts.

I noticed it when I unplugged my tv aerial and rested my hand on a
computer case while doing it. It frightened me out of my already
depleted wits.

You can blow the main trip if you short circuit those wires on a
socket or light fitting, even when the live for the circuit is
disconnected at the CU.

The opinion in here was that some equipment that does not use mains
transformers, (TVs, computers), sets up this voltage in the earth and
neutral wires. The reason that it appears on one socket and not
another is that it does not travel far from source due to being very
weak.

If you have the slightest doubt get it examined by an electrician to
put your mind at rest.

"D.M. Procida" wrote in
message
...
When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Daniele

I'd say on that particular mains socket the 'live' and 'neutral' pins are
connected the wrong way round.
The (normal nowadays) tingle is due to current leakage through a small EMC
filtering capacitor specifically fitted ACROSS! the supposed safety
isolation barrier of the switched mode power transformer.
These mains rated EMC capacitors seem fitted to all SMPS beyond a few watts
capacity and are the only viable, available means to allow passing the EMC
type tests.

The consequence is to allow mains to leak through to your equipment and
anything else connected to it. Hum loops and equipment failures are common
because of this.
Apparently this mains leakeage is safe!. What happens when a young kid sat
on a nice earthplane kitchen floor sucks on one of the outlet connectors?.
Seems outrageous that elf and safety haven't outright banned the sodding
things. The elephant sits slap bang in the middle of the room yet remains
invisible to those paid to protect us.

In article , Dave Plowman (News)
writes

There are commonly high value resistors between what is effectively mains
and the casing of such devices for RFI suppression purposes. And you can
feel a slight tingle from these under certain circumstances. Perfectly
safe, though.

ITYM capacitors, and low value.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

In article ,
wrote:
If you put a voltmeter across the earth and neutral connections you
may find a fairly high voltage exists between them.

One of my sockets has 110 volts across those wires. It varies on other
sockets down to a few volts.

You must have a problem somewhere. This house hasn't got PME, but the
voltage between them measures about 350 mV.

--
*Honk if you love peace and quiet*

Dave Plowman London SW
To e-mail, change noise into sound.

presented the following explanation :
If you put a voltmeter across the earth and neutral connections you
may find a fairly high voltage exists between them.

There might be a few volts, maybe 20 between N and E.


One of my sockets has 110 volts across those wires. It varies on other
sockets down to a few volts.

There should be no large variation when checked between the N & E of
one circuit and the N & E of another. The actual voltage can wonder
about a bit though due to various factors. I would be quite concerned
if I saw 110v.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Dave Plowman (News) wrote:
In article ,
wrote:
If you put a voltmeter across the earth and neutral connections you
may find a fairly high voltage exists between them.

One of my sockets has 110 volts across those wires. It varies on other
sockets down to a few volts.

You must have a problem somewhere. This house hasn't got PME, but the
voltage between them measures about 350 mV.


Sounds like the Earth on the affected circuit has become open-circuit
from the Consumer Unit, and another appliance on the same circuit with
normal capacitive filtering is bringing the now-floating 'earth' up to
1/2 mains potential.

--
Ron

In message , Piers Finlayson
writes



On 25/08/2009 09:16, in article
, "D.M.
Procida" wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

I get this whenever I
- use my MBP on the train and
- plug the power adaptor into the in-seat (table) power and
- rest one arm on the MBP and the other on the (presumably metal, earthed)
arm-rest.

It can actually be quite painful - like a stinging more than a tingling.
This might be because it comes through the underside of my fore-arm which is
more sensitive than fingers or the back of the arm.

I've meant to try using the long power lead with the power supply, instead
of just the stubby plug thing (which doesn't have an earth). I haven't
because I can't find it...

I've also not wanted to use a multimeter on it on the train because of the
strange looks and/or accusations of terrorism which may ensue.

"Don't anyone move - I've got a Fluke, and I know how to use it !"

Don't be such a wuss

--
geoff

geoff wrote:
In message , Piers Finlayson
writes



On 25/08/2009 09:16, in article
,
"D.M.
Procida" wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

I get this whenever I
- use my MBP on the train and
- plug the power adaptor into the in-seat (table) power and
- rest one arm on the MBP and the other on the (presumably metal,
earthed)
arm-rest.

It can actually be quite painful - like a stinging more than a tingling.
This might be because it comes through the underside of my fore-arm
which is
more sensitive than fingers or the back of the arm.

I've meant to try using the long power lead with the power supply,
instead
of just the stubby plug thing (which doesn't have an earth). I haven't
because I can't find it...

I've also not wanted to use a multimeter on it on the train because of
the
strange looks and/or accusations of terrorism which may ensue.

"Don't anyone move - I've got a Fluke, and I know how to use it !"

Don't be such a wuss

Being an electrician on a train has a historially high mortality rate...

I've also not wanted to use a multimeter on it on the train because of the
strange looks and/or accusations of terrorism which may ensue.

"Don't anyone move - I've got a Fluke, and I know how to use it !"

Don't be such a wuss

TBH I'm more worried about looking like a weirdo than a terrorist. But
perhaps it's too late for that ...

In message , The Natural Philosopher
writes
geoff wrote:
In message , Piers Finlayson
writes



On 25/08/2009 09:16, in article
,
"D.M.
Procida" wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

I get this whenever I
- use my MBP on the train and
- plug the power adaptor into the in-seat (table) power and
- rest one arm on the MBP and the other on the (presumably metal,
earthed)
arm-rest.

It can actually be quite painful - like a stinging more than a tingling.
This might be because it comes through the underside of my fore-arm
which is
more sensitive than fingers or the back of the arm.

I've meant to try using the long power lead with the power supply,
instead
of just the stubby plug thing (which doesn't have an earth). I haven't
because I can't find it...

I've also not wanted to use a multimeter on it on the train because
of the
strange looks and/or accusations of terrorism which may ensue.

"Don't anyone move - I've got a Fluke, and I know how to use it !"
Don't be such a wuss

Being an electrician on a train has a historially high mortality
rate...

But only if you're (in the eyes of the peelers) a shifty looking
forriner


--
geoff

In message , Piers Finlayson
writes


I've also not wanted to use a multimeter on it on the train because of the
strange looks and/or accusations of terrorism which may ensue.

"Don't anyone move - I've got a Fluke, and I know how to use it !"

Don't be such a wuss

TBH I'm more worried about looking like a weirdo than a terrorist. But
perhaps it's too late for that ...

Never been a morris dancer, then ?

--
geoff

In article ,
John Rumm wrote:
Apparently this mains leakeage is safe!. What happens when a young
kid sat on a nice earthplane kitchen floor sucks on one of the outlet
connectors?. Seems outrageous that elf and safety haven't outright
banned the sodding things. The elephant sits slap bang in the middle
of the room yet remains invisible to those paid to protect us.

One typically chooses filter capacitor values such that the reactance at
mains frequency is such that they can only pass relatively small
currents, certainly not enough to kill or injure.

I've known quite a few small value ceramic capacitors fail short circuit -
but on low voltage DC circuits. Do they use some special type that
positively can't do this?

--
*Everyone has a photographic memory. Some just don't have film*

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
writes

I've known quite a few small value ceramic capacitors fail short circuit -
but on low voltage DC circuits. Do they use some special type that
positively can't do this?

Yes, you can get safety rated capacitors for this job:

Class X capacitors are safe to use between line and neutral where
failure would not expose the user to a shock but where a fault would
need to be cleared in a safe manner.

and

Class Y capacitors are safe to use between line and earth or other
positions[1] where failure could expose the user to a shock.

[1] eg across a double insulated (or reinforced insulation) barrier such
as between input and output of an unearthed (class 2) switched mode
power supply, as discussed on this thread.

Commonly available as metal film or ceramic, ceramic better for HF
suppression due to their construction.

Class X:
http://cpc.farnell.com/CA06046

Class X/Y (dual purpose):
http://cpc.farnell.com/CA06001
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

On Thu, 27 Aug 2009 10:29:02 +0100, fred wrote:
Class X capacitors are safe to use between line and neutral where
failure would not expose the user to a shock but where a fault would
need to be cleared in a safe manner.

And holy cow do they ever generate a lot of smoke and make a mess when
they do fail :-) (I've replaced many a one in vintage equipment - and
they have a habit of seeming fine in something which hasn't powered
up in years, but then abruptly let go after an hour or two of running)

All the old ones seem to be rated to 250V - a lot of the newer ones are
rated to 275V. I'm not sure if the failures of the original parts are
purely down to age, or if the lower operating margin contributes in some
way.

cheers

Jules

On Thu, 27 Aug 2009 13:02:05 +0100, John Rumm wrote:

Dave Plowman (News) wrote:


I've known quite a few small value ceramic capacitors fail short circuit -
but on low voltage DC circuits. Do they use some special type that
positively can't do this?

They do. Many are designed to be internally fusible as well. There are
also various rules requiring them to be self extinguishing as well IIRC.

Unfortunately, many major manufacturers and suppliers source quite a lot of
their stuff from China, and I wouldn't like to assert that everything that
comes out of China meets all the various rules and regulations that hold in
the west.


--
The Wanderer

It pays to buy things you dislike. They last much longer.

John Rumm wrote:
john jardine wrote:

Apparently this mains leakeage is safe!. What happens when a young kid sat
on a nice earthplane kitchen floor sucks on one of the outlet connectors?.
Seems outrageous that elf and safety haven't outright banned the sodding
things. The elephant sits slap bang in the middle of the room yet remains
invisible to those paid to protect us.

One typically chooses filter capacitor values such that the reactance at
mains frequency is such that they can only pass relatively small
currents, certainly not enough to kill or injure.

(also you need to be able to have a bunch of them on a circuit and not
trip a 30mA threshold RCD!)

--
Cheers,

John.

Indeed.
At this location though, I've now so much SMPS kit hooked up (I'm
stuck with the ****e), that just an extra 5-10ma of leakage trips the
lab 30ma RCD!.

As a good reference source for low power SMPS designs I use ...
http://www.powerint.com/en/design-su...esign-examples

And a good discussion of the SMPS power supply leakage problem is
here ...
http://sound.westhost.com/articles/external-psu.htm

The Rod Elliot site shows the common 2 filtering capacitor setup,
hence the reason for 120Vac sitting on the DC output.
The TopSwitch people seem to use EMC cap' values up to 4n7, which
implies about 0.4ma mains leakage ,(rising to amps under transient
connection conditions) but I've a suspicion I've seen research into
'onset of fibrillation ma levels' not too far up from this value.
Also, I had a lab wall wart PSU, that I found had a 275Vac Varistor
fitted instead of the X rated filter cap. Fine for months, then the
Varistor started leaking badly and blew £200 of connected test kit.

Gimme Victorian technology, 50Hz, heavy metal transformers, any day!

In message . com, Jules
writes
On Thu, 27 Aug 2009 10:29:02 +0100, fred wrote:
Class X capacitors are safe to use between line and neutral where
failure would not expose the user to a shock but where a fault would
need to be cleared in a safe manner.

And holy cow do they ever generate a lot of smoke and make a mess when
they do fail :-) (I've replaced many a one in vintage equipment - and
they have a habit of seeming fine in something which hasn't powered
up in years, but then abruptly let go after an hour or two of running)

Smelly tar, don't forget the smelly tar

All the old ones seem to be rated to 250V - a lot of the newer ones are
rated to 275V. I'm not sure if the failures of the original parts are
purely down to age, or if the lower operating margin contributes in some
way.
--
geoff

DaveN wrote:

On 25 Aug, 09:16, (D.M.
Procida) wrote:
When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Daniele

This is normal for metal-cased laptops, as they are not double-
insulated. The tingle you feel is leakage current through the power
supply capacitors. This should go away if you use the full mains lead
instead of the plastic 3-pin adaptor, as the former is has a proper
earth connection to the supply).

If you measure the potential of the case with respect to earth, using
a high-impedance multimeter, you'll see that your laptop is at ~120V.
This is not a fault.

So why does it not happen using the same equipment on another socket?
That's the slightly troubling puzzle.

Daniele

The Wanderer wrote:

On Tue, 25 Aug 2009 09:16:32 +0100, D.M. Procida wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

Have you checked only with one socket (oe double socket if that's the case)
on each ring?

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Nothing springs immediately to mind other than to ask, have you checked the
socket is wired correctly?

Using a plug-in tester - it reports everything correct.

Daniele

In article
,
D.M. Procida wrote:
If you measure the potential of the case with respect to earth, using
a high-impedance multimeter, you'll see that your laptop is at ~120V.
This is not a fault.

So why does it not happen using the same equipment on another socket?
That's the slightly troubling puzzle.

Socket in the same room? I'd check them out. If in another room more
likely the floor material providing a better earth path.

--
*Snowmen fall from Heaven unassembled*

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

If you measure the potential of the case with respect to earth, using
a high-impedance multimeter, you'll see that your laptop is at ~120V.
This is not a fault.

So why does it not happen using the same equipment on another socket?
That's the slightly troubling puzzle.

Socket in the same room? I'd check them out. If in another room more
likely the floor material providing a better earth path.

No, different rooms. In both cases though the floors are wood (one
carpeted) and I was wearing rubber-soled footwear.

Daniele