I noticed a tingling from contact with a USB lead of an external Hard Drive.

Investigating this led to the PSU, the plug of which has a high voltage
on the outer connector compared with house earth. It was varying between
70 and 110V.

(I did not check the voltage of the output which I have no reason to
doubt was correct - 12V I think it should be)

The PSU is a three pin plug. Presumably the earth connection is not
being used.

Is the PSU faulty?

aeio prodded the keyboard

I noticed a tingling from contact with a USB lead of an external
Hard Drive.

Investigating this led to the PSU, the plug of which has a high
voltage on the outer connector compared with house earth. It was
varying between 70 and 110V.

(I did not check the voltage of the output which I have no reason to
doubt was correct - 12V I think it should be)

The PSU is a three pin plug. Presumably the earth connection is not
being used.

Is the PSU faulty?

Check the outer shell to earth pin with an ohmeter.

--
Best Regards:
Baron.

On 7/24/2014 11:35 AM, Baron wrote:
aeio prodded the keyboard

I noticed a tingling from contact with a USB lead of an external
Hard Drive.

Investigating this led to the PSU, the plug of which has a high
voltage on the outer connector compared with house earth. It was
varying between 70 and 110V.

(I did not check the voltage of the output which I have no reason to
doubt was correct - 12V I think it should be)

The PSU is a three pin plug. Presumably the earth connection is not
being used.

Is the PSU faulty?

Check the outer shell to earth pin with an ohmeter.

I'd expect that the output is nominally floating with respect
to the AC input port.
There usually are caps between line side and DC for EMI reasons.

I had a computer supply with a bad cap in the 5V standby supply.
Caused the GFI to trip.
Never did figure out the relationship between the cap
and the symptom, but the cap fixed it.

Hello Mike,
mike prodded the keyboard

On 7/24/2014 11:35 AM, Baron wrote:
aeio prodded the keyboard

I noticed a tingling from contact with a USB lead of an external
Hard Drive.

Investigating this led to the PSU, the plug of which has a high
voltage on the outer connector compared with house earth. It was
varying between 70 and 110V.

(I did not check the voltage of the output which I have no reason
to doubt was correct - 12V I think it should be)

The PSU is a three pin plug. Presumably the earth connection is
not being used.

Is the PSU faulty?

Check the outer shell to earth pin with an ohmeter.

I'd expect that the output is nominally floating with respect
to the AC input port.
There usually are caps between line side and DC for EMI reasons.

I had a computer supply with a bad cap in the 5V standby supply.
Caused the GFI to trip.
Never did figure out the relationship between the cap
and the symptom, but the cap fixed it.

When he mentioned "outer connector" I thought he meant the shell on
it. My external USB HDD has the ground connection carried right
through to the mains earth pin. I have continuity all the way from
the metal drive case.


--
Best Regards:
Baron.

On 24/07/14 19:35, Baron wrote:
aeio prodded the keyboard

I noticed a tingling from contact with a USB lead of an external
Hard Drive.

Investigating this led to the PSU, the plug of which has a high
voltage on the outer connector compared with house earth. It was
varying between 70 and 110V.

(I did not check the voltage of the output which I have no reason to
doubt was correct - 12V I think it should be)

The PSU is a three pin plug. Presumably the earth connection is not
being used.

Is the PSU faulty?

Check the outer shell to earth pin with an ohmeter.


I had it packed to return actually - but have opened it up again - and
see the earth pin is non conductive.

On Thursday, July 24, 2014 10:02:01 AM UTC-7, aeio wrote:
I noticed a tingling from contact with a USB lead of an external Hard Drive.


Investigating this led to the PSU, the plug of which has a high voltage
on the outer connector compared with house earth. It was varying between
70 and 110V.

A voltmeter might pick up leakage, but to determine if it's hazardous, you
need a load. I'd start with AC milliamp scale (try on high amp scale first, of course)
to test further. It's probably a bad PSU just as you suspect (if you feel it
it's maybe a few milliamps, but microamps might be acceptable).
Connect one probe to ground, the other to the touchable metal part.

The 'correct' way to test involves a dive into a variety of national and
international standards. One half milliamp into 1500 ohms parallel with
0.15 uF, is a typical 'safe' threshold.

On 24/07/14 19:39, whit3rd wrote:
On Thursday, July 24, 2014 10:02:01 AM UTC-7, aeio wrote:
I noticed a tingling from contact with a USB lead of an external Hard Drive.


Investigating this led to the PSU, the plug of which has a high voltage
on the outer connector compared with house earth. It was varying between
70 and 110V.

A voltmeter might pick up leakage, but to determine if it's hazardous, you
need a load. I'd start with AC milliamp scale (try on high amp scale first, of course)
to test further. It's probably a bad PSU just as you suspect (if you feel it
it's maybe a few milliamps, but microamps might be acceptable).
Connect one probe to ground, the other to the touchable metal part.

The 'correct' way to test involves a dive into a variety of national and
international standards. One half milliamp into 1500 ohms parallel with
0.15 uF, is a typical 'safe' threshold.

slowly going up and down between 0 and .005 milliamps - on a cheap
multimeter.

Is it worth trying it with a capacitor?

aeio prodded the keyboard

On 24/07/14 19:39, whit3rd wrote:
On Thursday, July 24, 2014 10:02:01 AM UTC-7, aeio wrote:
I noticed a tingling from contact with a USB lead of an external
Hard Drive.


Investigating this led to the PSU, the plug of which has a high
voltage on the outer connector compared with house earth. It was
varying between 70 and 110V.

A voltmeter might pick up leakage, but to determine if it's
hazardous, you
need a load. I'd start with AC milliamp scale (try on high amp
scale first, of course)
to test further. It's probably a bad PSU just as you suspect (if
you feel it it's maybe a few milliamps, but microamps might be
acceptable). Connect one probe to ground, the other to the
touchable metal part.

The 'correct' way to test involves a dive into a variety of
national and international standards. One half milliamp into 1500
ohms parallel with 0.15 uF, is a typical 'safe' threshold.

slowly going up and down between 0 and .005 milliamps - on a cheap
multimeter.

Is it worth trying it with a capacitor?

A reading that small could just as well be leakage. Are you sure that
should be milliampere and not amps ? ie 5 ma.


--
Best Regards:
Baron.

On 24/07/14 22:08, Baron wrote:
aeio prodded the keyboard

On 24/07/14 19:39, whit3rd wrote:
On Thursday, July 24, 2014 10:02:01 AM UTC-7, aeio wrote:
I noticed a tingling from contact with a USB lead of an external
Hard Drive.


Investigating this led to the PSU, the plug of which has a high
voltage on the outer connector compared with house earth. It was
varying between 70 and 110V.

A voltmeter might pick up leakage, but to determine if it's
hazardous, you
need a load. I'd start with AC milliamp scale (try on high amp
scale first, of course)
to test further. It's probably a bad PSU just as you suspect (if
you feel it it's maybe a few milliamps, but microamps might be
acceptable). Connect one probe to ground, the other to the
touchable metal part.

The 'correct' way to test involves a dive into a variety of
national and international standards. One half milliamp into 1500
ohms parallel with 0.15 uF, is a typical 'safe' threshold.

slowly going up and down between 0 and .005 milliamps - on a cheap
multimeter.

Is it worth trying it with a capacitor?

A reading that small could just as well be leakage. Are you sure that
should be milliampere and not amps ? ie 5 ma.

Yes - 0.005 mA. That is on the 2mA scale. There is nothing showing on
the higher scales and nothing on the AC scale.

aeio prodded the keyboard

On 24/07/14 22:08, Baron wrote:
aeio prodded the keyboard

On 24/07/14 19:39, whit3rd wrote:
On Thursday, July 24, 2014 10:02:01 AM UTC-7, aeio wrote:
I noticed a tingling from contact with a USB lead of an external
Hard Drive.


Investigating this led to the PSU, the plug of which has a high
voltage on the outer connector compared with house earth. It was
varying between 70 and 110V.

A voltmeter might pick up leakage, but to determine if it's
hazardous, you
need a load. I'd start with AC milliamp scale (try on high amp
scale first, of course)
to test further. It's probably a bad PSU just as you suspect (if
you feel it it's maybe a few milliamps, but microamps might be
acceptable). Connect one probe to ground, the other to the
touchable metal part.

The 'correct' way to test involves a dive into a variety of
national and international standards. One half milliamp into
1500 ohms parallel with 0.15 uF, is a typical 'safe' threshold.

slowly going up and down between 0 and .005 milliamps - on a cheap
multimeter.

Is it worth trying it with a capacitor?

A reading that small could just as well be leakage. Are you sure
that should be milliampere and not amps ? ie 5 ma.

Yes - 0.005 mA. That is on the 2mA scale. There is nothing showing
on the higher scales and nothing on the AC scale.

In that case I would be inclined to forget about it. But just in case
check it regularly to make sure it isn't getting worse.

--
Best Regards:
Baron.