Electric shocks (was: 100V appliance on 110v power supply)

[TJ Hertz]

When I said "I've got a Japanese Akai S1000 sampler", I actually meant "I'm
selling a Japanese Akai S1000 sampler for someone else". As a result, I
didn't know much about the unit and its condition.

But I asked the owner what she used to do with regards to power supply and
she gave me the transformer that she had been running it off for the past 7
years or so. Surprise surprise - it's a 240V to 115V transformer, and she
said the Akai always worked fine despite being labelled 100V. In other
words, she'd been using an incorrect transformer for years, but it worked
anyway.

A buyer emailed me today from eBay asking if the screen was still bright or
if it had gone dim with age, so I plugged in the sampler using
aforementioned 115V transformer and promptly got an electric shock from an
area on the sampler's case where a bit of the paint had been scratched off,
leaving bare metal. It is worth bearing in mind that I was barefoot and
standing on a concrete garage floor, but nevertheless, this shouldn't
happen. I plugged it in again and the same thing happened. However, when
turned on, the sampler worked fine - it just gave me a shock whenever I
touched the case (a sizeable electric shock, not like static). The owner
said that she'd never experienced this before despite using the sampler with
the same transformer on a UK mains supply.

One thing I noticed about the unit was that it used a 2-pin power lead with
apparently no earth. As in, the socket on the machine only had 2 pins, so
there was no option to use an earthed cable (even though the transformer had
earthed sockets). What's the deal with this? Can anything be done? Obviously
I can't sell a unit on eBay in Very Good Condition if it shocks you when you
plug it in, even if it works fine otherwise.

Is my only option to sell it as-seen with a buyer warning?

Thanks,

 

[Richard Crowley]

When I said "I've got a Japanese Akai S1000 sampler",
I actually meant "I'm selling a Japanese Akai S1000 sampler
for someone else". As a result, I didn't know much about
the unit and its condition.

But I asked the owner what she used to do with regards to
power supply and she gave me the transformer that she had
been running it off for the past 7 years or so. Surprise surprise
- it's a 240V to 115V transformer, and she said the Akai
always worked fine despite being labelled 100V. In other
words, she'd been using an incorrect transformer for years,
but it worked anyway.

Generously-designed equipment can likely take a 15% over-
voltage although it may run warmer (and may reduce its expected
lifespan.) But lots of modern equipment is designed on the very
edge of acceptable ranges, so I wouldn't try it as a rule.

A buyer emailed me today from eBay asking if the screen was
still bright or if it had gone dim with age, so I plugged in the
sampler using aforementioned 115V transformer and promptly
got an electric shock from an area on the sampler's case where
a bit of the paint had been scratched off, leaving bare metal. It
is worth bearing in mind that I was barefoot and standing on a
concrete garage floor, but nevertheless, this shouldn't happen.
I plugged it in again and the same thing happened. However,
when turned on, the sampler worked fine - it just gave me a
shock whenever I touched the case (a sizeable electric shock,
not like static). The owner said that she'd never experienced
this before despite using the sampler with the same transformer
on a UK mains supply.

PLEASE DON'T do that experiment again. We would miss you
if you electrocuted yourself! Seriously! There are SAFE ways
of testing for this that don't put your life or limb at risk.

One thing I noticed about the unit was that it used a 2-pin power
lead with apparently no earth. As in, the socket on the machine
only had 2 pins, so there was no option to use an earthed cable
(even though the transformer had earthed sockets). What's the
deal with this? Can anything be done? Obviously I can't sell a unit
on eBay in Very Good Condition if it shocks you when you plug
it in, even if it works fine otherwise.
Is my only option to sell it as-seen with a buyer warning?

Now that you know about it, and especially now that you have
revealed it in public, you really have no ethical choice but to
disclose it to any potential buyer. If somebody bought it and
electrocuted themselves full disclosure would be your minimum
defense.

If it were me, I would be tempted to fit an IEC power connector
on it (like the kind used for computers), with the green-wire
ground securely bonded to the metal chassis. But mains wiring
is not a project for amateurs. I would think that most consumer
equipment service shops ("TV Repair", etc.) would be equipped
for and experienced with testing and fixing this kind of problem.

Ironically, it may be working just as it was designed back
when it was first sold. But you can't get away without telling
bidders about the hazard today IMHO.

 

[Beachcomber]

One thing I noticed about the unit was that it used a 2-pin power lead with
apparently no earth. As in, the socket on the machine only had 2 pins, so
there was no option to use an earthed cable (even though the transformer had
earthed sockets). What's the deal with this? Can anything be done? Obviously
I can't sell a unit on eBay in Very Good Condition if it shocks you when you
plug it in, even if it works fine otherwise.

Is my only option to sell it as-seen with a buyer warning?

If you sell this product, even with a warning, you are opening up
yourself to servere liability issues.

An electric shock can be painful under the best conditions and
potentially deadly under the worst conditons.

It's likely that the transformer that the person you bought this from
was providing isolation and hence their claim of no shocks may have
valid.

Beachcomber

 

[operator jay]

...

Someone pointed out the online manual. It has specific mention of earthing
in certain regions. You might want to take a look. Maybe something there
will be worth knowing.

j

 

[TJ Hertz]

...

Generously-designed equipment can likely take a 15% over-
voltage although it may run warmer (and may reduce its expected
lifespan.) But lots of modern equipment is designed on the very
edge of acceptable ranges, so I wouldn't try it as a rule.


PLEASE DON'T do that experiment again. We would miss you
if you electrocuted yourself! Seriously! There are SAFE ways
of testing for this that don't put your life or limb at risk.


Now that you know about it, and especially now that you have
revealed it in public, you really have no ethical choice but to
disclose it to any potential buyer. If somebody bought it and
electrocuted themselves full disclosure would be your minimum
defense.

Yeah, I know, and that's probably what I'll do - I was just asking if there
were any ways of fixing it. Obviously if the problem remains I will warn any
buyer.

If it were me, I would be tempted to fit an IEC power connector
on it (like the kind used for computers), with the green-wire
ground securely bonded to the metal chassis. But mains wiring
is not a project for amateurs. I would think that most consumer
equipment service shops ("TV Repair", etc.) would be equipped
for and experienced with testing and fixing this kind of problem.

Ironically, it may be working just as it was designed back
when it was first sold. But you can't get away without telling
bidders about the hazard today IMHO.

I'll take it into a repair shop methinks. Thanks for the help.

TJ

 

[Don Kelly]

When I said "I've got a Japanese Akai S1000 sampler", I actually meant "I'm
selling a Japanese Akai S1000 sampler for someone else". As a result, I
didn't know much about the unit and its condition.

But I asked the owner what she used to do with regards to power supply and
she gave me the transformer that she had been running it off for the past 7
years or so. Surprise surprise - it's a 240V to 115V transformer, and she
said the Akai always worked fine despite being labelled 100V. In other
words, she'd been using an incorrect transformer for years, but it worked
anyway.

A buyer emailed me today from eBay asking if the screen was still bright or
if it had gone dim with age, so I plugged in the sampler using
aforementioned 115V transformer and promptly got an electric shock from an
area on the sampler's case where a bit of the paint had been scratched off,
leaving bare metal. It is worth bearing in mind that I was barefoot and
standing on a concrete garage floor, but nevertheless, this shouldn't
happen. I plugged it in again and the same thing happened. However, when
turned on, the sampler worked fine - it just gave me a shock whenever I
touched the case (a sizeable electric shock, not like static). The owner
said that she'd never experienced this before despite using the sampler with
the same transformer on a UK mains supply.

One thing I noticed about the unit was that it used a 2-pin power lead with
apparently no earth. As in, the socket on the machine only had 2 pins, so
there was no option to use an earthed cable (even though the transformer had
earthed sockets). What's the deal with this? Can anything be done? Obviously
I can't sell a unit on eBay in Very Good Condition if it shocks you when you
plug it in, even if it works fine otherwise.

Is my only option to sell it as-seen with a buyer warning?

Thanks,

It appears that the original usage was 240V to ground and the transformer is
an autotransformer. Using this transformer with a North American 240/120V
system could put the case at 120V with respect to ground.
If this unit is to be used with a transformer, it will require an isolating
(2 winding) 240/120V transformer and then the case can be grounded.

However, why use the transformer?

Why not connect directly to the 120V outlet. It will be necessary to
determine which lead is the neutral. You will need a voltmeter. If the case
is at 120 or so Volts to ground- reverse the wires to the plug. Check
again-you want a small or negligable voltage between case and ground. Then
set up the plug and leads accordingly (replacing the cord and plug to a 3
prong (hot, neutral and ground) is the best way.
If you have any doubts, a competent electrician can sort it out for you in a
short time- or you warn the potential buyer that it appears that the case is
tied to the neutral and you don't know which wire is neutral and leave the
correction to him/her. You don't want to be responsible for avoidable
injuries.

 

[TJ Hertz]

It appears that the original usage was 240V to ground and the
transformer is an autotransformer. Using this transformer with a
North American 240/120V system could put the case at 120V with
respect to ground.
If this unit is to be used with a transformer, it will require an
isolating (2 winding) 240/120V transformer and then the case can be
grounded.

However, why use the transformer?

Why not connect directly to the 120V outlet. It will be necessary to
determine which lead is the neutral. You will need a voltmeter. If
the case is at 120 or so Volts to ground- reverse the wires to the
plug. Check again-you want a small or negligable voltage between case
and ground. Then set up the plug and leads accordingly (replacing
the cord and plug to a 3 prong (hot, neutral and ground) is the best
way.
If you have any doubts, a competent electrician can sort it out for
you in a short time- or you warn the potential buyer that it appears
that the case is tied to the neutral and you don't know which wire is
neutral and leave the correction to him/her. You don't want to be
responsible for avoidable injuries.

So basically, you're saying find out which way the thing should be connected
in order to let the case be neutral, replace the mains end of the cable with
a 3-pin plug so that it can't be connected the wrong way, and glue/fix the
sampler end of the cable into the sampler so it can't be reversed (or label
which way it should go)? And this would fix the electric shock problem, but
still leave the unit unearthed?

I'll let an electrician deal with it because I have neither a
volt/multimeter nor any spare 3-pin plugs (you don't see many in the UK),
but I'd like to know what's going on anyway.

Thanks

 

[Steve Urbach]

...

Are those common in England? I've never seen any.

On the shaving mirror in hotels <G>. I just would not plug good
electronics into it :O


, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw [email protected]
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

 

[Andrew Gabriel]

On the shaving mirror in hotels <G>. I just would not plug good
electronics into it :O

Should be no problem, except they are limited to 25W with
a slow acting thermal cutout. The output is isolated via
an isolating transformer (floating).

 

[w_tom]

Ioslation transformer must still have the secondary (the 120
volt side) connected back to the building safety ground. If
not, then the appliance will 'float' - can become electrically
hot. If the transformer is properly designed, then either it
has such a connection OR it has a dedicated grounding wire
terminal to make that necessary connection.

 

[Phil Allison]

"w_tom"

Ioslation transformer must still have the secondary (the 120
volt side) connected back to the building safety ground.

** Making it no longer an "isolation " transformer.

If not, then the appliance will 'float' - can become electrically
hot.

** The appliance's AC supply wiring will float - but nothing else since
it is all insulated from that wiring.

If the transformer is properly designed, then either it
has such a connection OR it has a dedicated grounding wire
terminal to make that necessary connection.

** A step-down / isolation transformer ought to have a ground terminal on
the outlet that connects to the METALWORK of the appliance via the third pin
of the plug.




........... Phil

 

[Roy Q.T.]

From: [email protected] (Phil Allison)
"w_tom"
  Ioslation transformer must still have the secondary (the 120 volt
side) connected back to the building safety ground.
** Making it no longer an "isolation " transformer.
If not, then the appliance will 'float' - can become electrically
hot.
** The appliance's AC supply wiring will float - but nothing else since
it is all insulated from that wiring.
If the transformer is properly designed, then either it has such a
connection OR it has a dedicated grounding wire terminal to make that
necessary connection.
** A step-down / isolation transformer ought to have a ground terminal
on the outlet that connects to the METALWORK of the appliance via the
third pin of the plug.
..........   Phil

All those observations seem all for naught to me, since he as a Hot
Chassis Item.
It behooves whom ever get's to keep it to isolate the works 100% from
that chassis with plastic or insulated offsets to avoid any
objectionable current flowing through it as he's experienced., Or keep
it as is and Fancy Oneself in those days.

Point: No Manner of Transformer will correct the condition & a seperate
ground conductor will only disguise the fault.

He should have plugged it in his safe insulated floored section, but
then again it was all for the better

®oy

 

[Scott Dorsey]

Ioslation transformer must still have the secondary (the 120
volt side) connected back to the building safety ground. If
not, then the appliance will 'float' - can become electrically
hot. If the transformer is properly designed, then either it
has such a connection OR it has a dedicated grounding wire
terminal to make that necessary connection.

No, that's the point of isolation. Because the appliance floats, it can
become "hot" but the leakage current has no reference to the building
ground so if you touch the hot case, no current will flow through you.

Not that a safety ground isn't _still_ a good idea, mind you.
--scott

 

[Dimitrios Tzortzakakis]

Yes, that's why in all around the world the neutral of LV distribution
transformers is earthed (so I learned in my studies) so that you get
schocked and know that electricity is dangerous (no joke) AND because in a
neighborhood e.g. someone would be touching a live phase and someone else
another, so that both would be exposed to the line to line voltage which is
380 V in Europe (220 V in USA).However this happens only in LV, in MV, HV
and EHV there's no need for a reference to ground, because the windings of
the substation transformer are in delta, ungrounded.This doesn't make the
voltage not dangerous, I was told some horror stories back in Kozani.

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

 

[Andrew Gabriel]

Yes, that's why in all around the world the neutral of LV distribution
transformers is earthed (so I learned in my studies) so that you get
schocked and know that electricity is dangerous (no joke) AND because in a
neighborhood e.g. someone would be touching a live phase and someone else
another, so that both would be exposed to the line to line voltage which is
380 V in Europe (220 V in USA).However this happens only in LV, in MV, HV
and EHV there's no need for a reference to ground, because the windings of
the substation transformer are in delta, ungrounded.

They are often grounded even so, sometimes through a resistor
and current measuring equipment to monitor leakage in the line.
Also to prevent a transformer leak letting the lower voltage
windings float up to the voltage of the HV windings relative to
ground, which would exceed the insulation rating of the line and
downstream gear.

 

[w_tom]

If a transformer is properly grounded as required by codes,
then if the appliance has an internal short, that short will
trip a circuit breaker. Grounding transformer secondary is
necessary for breaker to trip. Leakage across to a floating
transformer secondary may put enough voltage on chassis to
cause shocks - with or without an internal appliance
problems. But transformer secondary must be safety grounded -
as codes require. When grounded, further useful information
(ie a tripping circuit breaker) would then tell us more,
immediately eliminate any human safety threat, and cause
humans on the scene to fix any existing problems. Even if the
appliance does have an internal fault, that fault would not be
fixed because a transformer secondary is not grounded.

BTW, I have assumed the appliance has a three prong
receptacle. I have mostly ignored a two prong receptacle
because the problem could be more complex. First most, does
the transformer have secondary properly safety grounded?

 

[Don Kelly]

Yes, that's why in all around the world the neutral of LV distribution
transformers is earthed (so I learned in my studies) so that you get
schocked and know that electricity is dangerous (no joke) AND because in a
neighborhood e.g. someone would be touching a live phase and someone else
another, so that both would be exposed to the line to line voltage which is
380 V in Europe (220 V in USA).However this happens only in LV, in MV, HV
and EHV there's no need for a reference to ground, because the windings of
the substation transformer are in delta, ungrounded.This doesn't make the
voltage not dangerous, I was told some horror stories back in Kozani.

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

---------------
In LV, MV , HV and RHV. the transformer windings can be and often are in Y.-
.. The most common connection is Delta Wye with the HV side in Wye with
direct or impedance grounding. There are good technical and economic reasons
for that. The next most common connection is probably Y-Y -delta for
supplying EHV lines . Note that even at 4160V distribution the supply
transformer is Y on the 4160V side.
Ground faults are the most common faults on transmission lines. This means
that the unfaulted phases will see overvoltages- not good. In addition,
protective relaying problems are increased and arcing faults which are not
detected and often undetectable can occur because of capacitive coupling.
The grounding eliminates these problems as well as problems due to the line
floating up and down due to atmospheric effects (thus stressing the
insulation). The use of a Y system makes life a lot easier.

--
Don Kelly
[email protected]
remove the urine to answer

 

[Don Kelly]

Sorry, given that it was e-bay, I didn't cjheck the origin. The solution
that I suggested was for North American usage.
The key in the UK case is to pitch the original transformer and get an
isolation transformer (2 winding 120/240V)

--
Don Kelly
[email protected]
remove the urine to answer

On the shaving mirror in hotels <G>. I just would not plug good
electronics into it :O


, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw [email protected]
, / / / Running United Devices "Cure For Cancer" Project 24/7

Have you helped? http://www.grid.org

 

[Roy Q.T.]

Fire Mouth: It So Happens It doesn't have a 3Prong plug, If You Had been
Attending the thread conscientiously you'd not assume erroneously ., and
he said the trany from japany is well grounded and supplies for
agrounded 3P plug, it is simply a hot chassis assembly and I stated he
can isolate it 100% from the circuits and supply with "stand offs" and
other plastic isolating materials if that is desirable., Shock Proofing
It !

The Fact that he got a harrowing Shock from it while testing it in his
cement floor garage is noteworthy enough to take measures to make the
Old For Sale Unit desirable of it's own volition irregardless of Supply.

Agreed: a Grounding conductor is always desirable and safest. Roy

From: [email protected] (w_tom)
    If a transformer is properly grounded as required by codes,
then if the appliance has an internal short, that short will trip a
circuit breaker.[ }:-oooh Not NEC ] Grounding transformer secondary is
necessary for breaker to trip. Leakage across to a floating transformer
secondary may put enough voltage on chassis to cause shocks - with or
without an internal appliance problems. But transformer secondary must
be safety grounded - as codes require. When grounded, further useful
information (ie a tripping circuit breaker) would then tell us more,
immediately eliminate any human safety threat, and cause humans on the
scene to fix any existing problems. Even if the appliance does have an
internal fault, that fault would not be fixed because a transformer
secondary is not grounded.
    BTW, I have assumed the appliance has a three prong
receptacle. I have mostly ignored a two prong receptacle because the
problem could be more complex. First most, does the transformer have
secondary properly safety grounded?
:
All those observations seem all for naught to me, since he as a Hot
Chassis Item.
It behooves whom ever get's to keep it to isolate the works 100% from
that chassis with plastic or insulated offsets to avoid any
objectionable current flowing through it as he's experienced., Or keep
it as is and Fancy Oneself in those days.
Point: No Manner of Transformer will correct the condition & a
separate ground conductor will only disguise the fault.
He should have plugged it in his safe insulated floored section, but
then again it was all for the better
®oy

 

[Rich Grise]

... promptly got an electric shock from an
area on the sampler's case where a bit of the paint had been scratched off,
leaving bare metal. It is worth bearing in mind that I was barefoot and
standing on a concrete garage floor, but nevertheless, this shouldn't
happen.

This is correct. Standing barefoot on a concrete garage floor while
dicking around with anything plugged into mains should never happen.

Good Luck - you'll need it.
Rich