[sdiy] Signals leaking into the PSU?

[Mike Bryant]

> There are literally loads of products on sale in the UK that break this rule though.

Oh boy tell me about it !   That's the problem with us adopting IEC regulations whilst trying to maintain the safest electrical system in the world.  The class Y capacitor is one of the worst inventions mankind ever made !

The rule of thumb used to be that class 2 products had to be less than 65W but that seems to have been gradually ignored.
Also the UK always had the 0.75mA maximum leakage which you couldn't feel, but to keep with world standards has accepted the 5mA leakage which as you say you most definitely can feel.

I would not expect any leakage to the lamp as there is no need to connect any supply to the metalwork so that would be double insulated and have always been legal.

The laptop exhibits the problem trading standards have.  It is legal to feel the 5mA through the USB because it's not a regular touching point, but you shouldn't really be feeling it through the anodised case.  To my mind that's still a failure so it would be interesting to hear what trading standards think.  Neither were legal pre the new 2020 regs, and companies are already taking liberties with it.  In fact I suspect the only reason we did accept the 5mA limit is because so much stuff was already on the market.  Trading standards have been confiscating high power electric scooters and similar with high powered class 2 chargers and metal handlebars, but one suspects that is only because the importers haven't the legal muscle of a Toshiba.

The other issue is that the laptop is deemed consumer, whereas PCs are deemed IT and even the IEC accepts that they should be grounded, at least for now.  They have a large document dictating how to earth IT racks for example and if you rack audio equipment (as in a modular synth) then that standard applies.

The problem is what the RoW deems safe, we historically haven't.  Only us (and countries that copy our regs) have fused plugs (again relaxed for low power items against many people's better judgement), shuttered sockets, redundancy in the mains wiring, and an enforced distinction between line and neutral with neutral rigidly connected to ground.  If you look at an older house you still often see the grounding wires that used to be on every radiator, then relaxed to just bathrooms, and now non-existent.  Unfortunately politicians haven't been willing to draw a line in the sand with the IEC regs so standards have dropped and more and more crap gets imported.



________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of rburnett at richieburnett.co.uk <rburnett at richieburnett.co.uk>
Sent: 20 February 2023 10:06
To: A.M. Barrio via Synth-diy <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Signals leaking into the PSU?

> ....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,
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