[sdiy] Signals leaking into the PSU?

[rburnett at richieburnett.co.uk]

> ....As I said, in the
> UK, exposed metal chassis must be connected to the mains earth.  You
> can choose to isolate all the electronics from it if you wish...

There are literally loads of products on sale in the UK that break this 
rule though.  Right now I have an anglepoise lamp and a free standing 
Ikea lamp next to me that both have a significant metal "chassis" but 
are marked as class-2.  There is no connection from mains earth to the 
metal parts, (there can't be because they only used 2 core cable to the 
plug!)  I also have an LG DVD player here that has a metal case but is 
marked class-2 with no earth bonding to the case and a captive 2-core 
mains cable.  Also I have a Toshiba work laptop with aluminium 
"cladding" over the back of the screen which is fed by a Class-2 
supply/charger.  You can clearly feel the "buzz" of the electricity on 
the aluminium cover if you run your fingers over it when it is plugged 
into the charger!

> Also if you perform live music, hold conferences with your own AV, or
> so on, the location's house electrician is supposed to check the
> chassis grounds on all your equipment are in place before he turns on
> the three-phase.

It causes all sorts of fun when Class-2 appliances meet Class-1 
appliances in larger setups.  For instance connecting a class-2 laptop 
or DVD player to a Class-1 (earthed) TV results in some tiny but pretty 
impressive sparks between the audio/video connectors when they come 
together.  It also hurts if you do this connection with the power on and 
manage to get your finger across the gap! (>.<)

> That may be true under the US regulations, but doesn't meet the
> current UK IET interpretation of a Class 2 FE device where the whole
> system is PAT tested, not the individual item.  You can use a
> wall-wart provided the item doesn't expose the output voltage across a
> major surface, for example a laptop can have USB sockets with up to
> 5mA of leakage (which I personally think is too high - the old 0.75mA
> limit was met by most equipment), but the case should be plastic or
> double insulated metal.

The Toshiba laptop clearly breaks this rule.  Aluminium plate appears to 
be anodised but you can still feel the electricity and get a meter 
reading of about 120VAC to ground!  Same on the USB surrounds.

-Richie,