Shock till DEATH by PSU

Hi,

1. I connect a normal 300/500v black cable to a PSU. The cable has NO
earthing wire.

See pic here:
http://www1.istockphoto.com/file_thu...ower_cable.jpg


2. I have a monitor with power on. I use the metal part of the blue
socket to touch the PSU.

See pic here: http://i15.ebayimg.com/05/i/06/b1/d6/ca_1_b.JPG

The trapezium shape metal plug is supposed to connect to earth right?


3. Now, the funny thing is spark comes out from the contact between the
PSU and the blue plug earthing wire. My assumption is that the brand
new PSU is faulty. Otherwise it is impossible for the metal PSU to
contain electricity.

But if I connect another cable with earth wire everything is fine and
of course without spark : -D

Any idea of what is happening? I don't want to get shocked one day and
till death.

<kennethlou@yahoo.com.hk> wrote in message
news:1162741277.693551.253370@m73g2000cwd.googlegr oups.com...
> Hi,
>
> 1. I connect a normal 300/500v black cable to a PSU. The cable has NO
> earthing wire.
>

<snip>

the power cord that goes to your powersupply *MUST* have an "earth" wire or
ground!

it's there for your safety.

If you use the proper cord, your machine will be safe.

If you use a grounded cord and your house circuit breaker or fues blows...
then your power supply is faulty...

kennethlou@yahoo.com.hk wrote:
> Hi,
>
> 1. I connect a normal 300/500v black cable to a PSU. The cable has NO
> earthing wire.
>
> See pic here:
> http://www1.istockphoto.com/file_thu...ower_cable.jpg
>
>
> 2. I have a monitor with power on. I use the metal part of the blue
> socket to touch the PSU.
>
You are seeing the small current from the mains
power emi filter,which is some coils and a few
capacitors to ground.
As you do not apply ground to the mains input,
you get about half the mains voltage(US 60 V, EUR 120),
but with a current which is not dangerous to you,
on the external case.
The (short) peakcurrent might fry an in/or output
circuit.
The same goes for the printer etc.
So especially in your case:connect the computer
first and the mains last.
However, try and use a groundwire, as the
interference with radio/tv will be much less, and
your hardware less liable to be killed.

kennethlou@yahoo.com.hk wrote:
> Hi,
>
> 1. I connect a normal 300/500v black cable to a PSU. The cable has NO
> earthing wire.
>
> See pic here:
> http://www1.istockphoto.com/file_thu...ower_cable.jpg
>
>
> 2. I have a monitor with power on. I use the metal part of the blue
> socket to touch the PSU.
>
> See pic here: http://i15.ebayimg.com/05/i/06/b1/d6/ca_1_b.JPG
>
> The trapezium shape metal plug is supposed to connect to earth right?
>
>
> 3. Now, the funny thing is spark comes out from the contact between the
> PSU and the blue plug earthing wire. My assumption is that the brand
> new PSU is faulty. Otherwise it is impossible for the metal PSU to
> contain electricity.
>
> But if I connect another cable with earth wire everything is fine and
> of course without spark : -D
>
> Any idea of what is happening? I don't want to get shocked one day and
> till death.
>

There is a schematic for an ATX PSU here. This schematic illustrates some
of the common features found in power supplies.

http://www.pavouk.comp.cz/hw/en_atxps.html

On the left hand side, is "Input Filter". Capacitors C2 and C3 connect to
the shield. The capacitors C2 and C3 were added to move high frequency
energy (electrical noise), to the shield. But some of the 50Hz or 60Hz
AC line current is also shunted into the shield. The shield should be
connected to earth ground, if at all possible. Otherwise, you may see
the symptoms you describe, where you can draw a spark between the shield
of connectors on the computer, and the shield of other devices connected
to the computer.

Once the shield (metal of the PSU and metal of the computer case) is
connected to earth ground, you won't see the sparks any more. Using
an earthed outlet makes this easy to do. Consult an electrician if
you seek to add earth ground, to AC wiring which lacks such a
provision. Electrical codes vary between countries, as to how
earth ground can be added. Some municipalities require wiring
changes to only be done by professionals.

Paul