being shocked by Amp casing

[RobZ]

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)

the amplifier is supplied by a 2 wire AC cord ( no earth )

what is causing this?

is this dangerous?

Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?

 

[Eeyore]

RobZ wrote:

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)

the amplifier is supplied by a 2 wire AC cord ( no earth )

what is causing this?

A switched-mode power supply almost without doubt. I imagine the amp is
compact and lighweight for its power rating.

is this dangerous?

As long as it's been designed to IEC standards, no. It's called 'leakage
current' and has allowable limits that will cause you no harm.

Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?

If the amp has a dedicated ground terminal do feel free to add a
*sepearate* 'earth wire' tot his. Otherwise don't tinker with the mains
witing AT ALL.

Graham

 

[Eeyore]

Tom Biasi wrote:

You are experiencing a ground loop.

I very much doubt it ! Inter-ground potentials should *never* be detectable
by touch. If they are, get an electrician QUICK !

Graham

 

[Eeyore]

christofire wrote:

"RobZ" <robert.zeilinga@standardbank.co.za> wrote

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)

the amplifier is supplied by a 2 wire AC cord ( no earth )

what is causing this?

is this dangerous?

Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?

Is it just a half-mains alternating voltage buzz? ... like you get when you
touch the metal casing of a two-wire-fed mains appliance like the Sony
DAV-S880 home theatre system, in which internal suppression/filter
capacitors connected to line and neutral appear to have their other ends
connected to the exposed metalwork!

If so, the current involved is too small to be dangerous - it's just a bit
disconcerting. You could add an earth but if the equipment is designed for
two-wire power then it probably isn't designed to have earth applied (others
will probably advise in this respect in more detail), and this could give
rise to an earth loop if anything feeding your amplifier is itself earthed.

Your answer is mostly corrrect in that you mention the effect of the suppresion
filter which by default must create a leakage current potential. There is
however, internally in the PSU typically another 'Y cap' that adds to the fun.

Graham

 

[Eeyore]

"Chungho@zongazonga.zip" wrote:

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)
the amplifier is supplied by a 2 wire AC cord ( no earth )
what is causing this?
is this dangerous?

Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?

Sounds like either your receptical is wired incorrectly or your
amp doesn't have a polarized plug and is plugged in reversed or
you have a problem inside your amp (system)....

The tingle you feel is because you aren't fully grounded yourself
as you are lying on the floor.. you are partially insulated.. But,
yes, this dangerous.. If you were to grab something that is
plugged in properly... You will complete the circuit causing a
severe shock... as it is likely that the case of something else
will/may be fully grounded.

This can also cause damage to your system if you connect one
item to a properly wired socket and another item in a socket that is
reversed. At minimum... you'll see sparks.

Inspect your wall sockets. The small blade is HOT and the large
blade is neutral/Ground (For US of course). Use a meter to measure
voltage in the socket. You should only get 120 (+ or - a few volts) ONLY if
the small blade is connected to one of your test leads. Otherwise the
socket is NOT wired correctly. Radio Shack used to sell three light
outlet testers.. (Basically three neon bulbs connected to the outlet blades
delta style...) not sure if they still do.... But try them out if your have
one near you...

Sorry, PURE NONSENSE.

I have seen tiny sparks in low light, interconnecting pieces of IT equipment.
ALL PERFECTLY LEGAL.

Graham

 

[Jasen Betts]

On 2008-07-09, RobZ <robert.zeilinga@standardbank.co.za> wrote:

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)

the amplifier is supplied by a 2 wire AC cord ( no earth )

what is causing this?

capacitance from live to the body of the amplifier,
if the power cord has a reversible plug on either end try reversing it.

is this dangerous?

if this is new equipment probably not.

Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?

almost certainly, especially if the maker has provided an earthing
terminal on the amplifier, but if you have other audio equipment that is
already earthed it may be better to earth your amp to that equipment.

Bye.
Jasen

 

[Eeyore]

Bob Masta wrote:

Eeyore wrote:
"Chungho@zongazonga.zip" wrote:

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)
the amplifier is supplied by a 2 wire AC cord ( no earth )
what is causing this?
is this dangerous?

Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?

Sounds like either your receptical is wired incorrectly or your
amp doesn't have a polarized plug and is plugged in reversed or
you have a problem inside your amp (system)....

The tingle you feel is because you aren't fully grounded yourself
as you are lying on the floor.. you are partially insulated.. But,
yes, this dangerous.. If you were to grab something that is
plugged in properly... You will complete the circuit causing a
severe shock... as it is likely that the case of something else
will/may be fully grounded.

This can also cause damage to your system if you connect one
item to a properly wired socket and another item in a socket that is
reversed. At minimum... you'll see sparks.

Inspect your wall sockets. The small blade is HOT and the large
blade is neutral/Ground (For US of course). Use a meter to measure
voltage in the socket. You should only get 120 (+ or - a few volts) ONLY if
the small blade is connected to one of your test leads. Otherwise the
socket is NOT wired correctly. Radio Shack used to sell three light
outlet testers.. (Basically three neon bulbs connected to the outlet blades
delta style...) not sure if they still do.... But try them out if your have
one near you...

Sorry, PURE NONSENSE.

I have seen tiny sparks in low light, interconnecting pieces of IT equipment.
ALL PERFECTLY LEGAL.


Maybe this can happen on perfectly legal systems, but the prudent
thing to do would be to check the receptacle first... there can be
some pretty strange wiring out there!

Many years ago, I was using a standard (back then) grounded-case
electric drill near an I-beam in my basement and got sparks. After
much exploratory surgery I finally found the problem: Some prior
owner had added a string of outlets while finishing the basement. He
had connected the run to a run from the mains, at a small junction box
in the ceiling. He had *reversed* the connections there (white to
black, black to white), and *cut off the grounds* !!! And then, to
make life even more interesting, he had drywalled over the junction
box area so everything looked normal. DUH!

Totally unrelated to this problem which is I will guarantee 99.99% certain to be
the use of filter caps in SMPSs that cause small leakage currents.

Graham

 

[Eeyore]

john jardine wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
RobZ wrote:

hi all, perhaps slightly off-topic but you guys have been of great
help to me in the past

When I was installing a new hifi amplifier last night, I realised i
was being lightly shocked each time i touched the amplifier case while
I was lying on the floor trying to re-route some of the speaker cables
behind the cabinet.

The shock is definatly between the Amplifier case and the floor. ( no
frayed wires - new installation)

the amplifier is supplied by a 2 wire AC cord ( no earth )

what is causing this?

A switched-mode power supply almost without doubt. I imagine the amp is
compact and lighweight for its power rating.


is this dangerous?

As long as it's been designed to IEC standards, no. It's called 'leakage
current' and has allowable limits that will cause you no harm.


Can I add my own earth wire ( joined to the case, to the AC socket
Earth Plug) ? will this help?

If the amp has a dedicated ground terminal do feel free to add a
*sepearate* 'earth wire' tot his. Otherwise don't tinker with the mains
witing AT ALL.


I'll second a leaky SMPS.
My 2amp SMPS 12V wall wart (double insulated) gave me a belt the other
night. Turns out there's 90Vac riding on the 12V connector. The bastard took
out an expensive bit of kit. Whole point of the bloody thing is to provide
galvanic isolation.
Never ever, had any trouble with cheap tat 50Hz transformer versions and
that's what I'm going back to.
I've had enough of EMI, noise, low level oscillations, expense, complexity
and unreliability. Sod the SM technology

FWIW you have my sympathies.

IEC 60065 allowable leakage current off the top of my head is 2.4mA or so.
What's more the MAIN culprit isn't even usually in the common mode filter but a
little known part that crosses the pri-sec isolation (a Y cap) to reduce EMC
compatability problems.

Graham