240volts and ground hum problems.

[The Dark force of dance]

Y-ellow Y'all.
	Just out of interest, does anyone have a definition of "Double Insulated"?

At 02:49 AM 06/13/99 +0100, Conrad Scott wrote:
>Peter Blackett wrote:
>> It's illegal in the UK to remove the earth connection on equipment to
>> stop ground loops [or for any other reason].
>
>AFAIK most of the EU standards for electronic equipment (safety etc.)
>apply to home-built stuff even if it's just for personal use and never
>taken out of the house.
>
>I can't imagine anyone getting into trouble on this but it's something
>to note (over here at least).

Australian mains is the same deal. Though there seems to be a great
discrepancy about what we're allowed to manufacture and use on our main and
what we're allowed to import and use on our mains. I've told this story
before but we've had lots of AKAI gear. All of it  had this curious mains
filter as you'd expect. A couple of chokes and a few caps to ground. Or in
this case, direct to the metal chassis of the gear. The thing is that this
gear was technically speaking, double insulated. IE: has only the 2 pins.
Neutral and Active. Now from my understanding, this is illegal. If it's a
metal chassis then it must be earthed. 

These things ended up dumping enough current into the chassis such that in
the wrong situation, you could touch the sampler and get a boot off it. And
this happened on all the AKAI gear we owned at the time. From an X7000 thru
S950. I don't remember if the apedgiator thing we had also did it. I got so
sick of getting a boot off of the X7000 that I replaced the proprietary
AKAI 2 pin mains connector for an IEC one. Connecting the Earth pin to the
Chassis. It did not create a hum loop but did stop us getting a kick off it
every time we tried to play it.

It beats me how they could get away with stuff like that?

So my understanding of double insulated gear is that it must be housed in
an all plastic case and no metal parts with any possible electrical
connection between the chassis and the user may be exposed. But whilst this
akai gear was listed as "double insulated" it seemed to not only break all
the rules but also be actually dangerous. Since then I've noticed lots of
gear which only have active and neutral connections and yet are in metal
and some times even 19" rack enclosures.

One could be forgiven for thinking that it was relying on the rack for
earth but I know this is also illegal under Australian wiring rules. In
fact you are supposed to have a separate ground wire to every separate
metal part or the chassis. You are not supposed to rely on the fact that
they are bolted together to form an earth.

The pain in the ass with earth loops under these conditions is that some
gear is earthed to the chassis. Some gear has a chassis which is earthed.
Some gear is isolated from chassis earth and some gear is isolated but
becomes connected when bolted into a rack. I've spent a great deal of my
life chasing humm loops. And people wonder why I like digital audio!

Mind you, if you want a real nightmare try hunting a digital hum loop.

Be absolutely Icebox.

 _ __        _                              
| "_ \      | |         batzman at all-electric.com / aek at all-electric.com
| |_)/  __ _| |_ ____           ALL ELECTRIC KITCHEN               
|  _ \ / _` | __|___ |  The Elementary Urban sanity CD
| |_) | (_| | |_  / /   out now on Transmission Communications
|_,__/ \__,_|\__|/ /    
                / ,__   http://www.all-electric.com
Goodfortune    |_____|