Dave Osborne
wibbled on Thursday 17 December 2009 19:37


By introducing an earth wire (or indeed armour/screening) into the
interior of the unit, you would then effectively make it a Class I
appliance. You would then have to make an electrical safety reassessment
of the product design. Depending on the nature of the product this could
be straightforward or it could be virtually impossible to achieve
without extensive design reworking.

Yes - I agree with all of that in spirit. But I don't make formal electrical
assessments when I build mains devices from scratch, other than common
sense, sensible design and good workmanship. I've applied more consideration
in my devices to making sure that a SELV part cannot reasonably contact a
mains part (due to wire falling off) than I've observed in at least one
appliance I took to bits once which had all the relevant markings on it.

I've built Class I and Class II appliances and applied the relevant
engineering considerations to both.

My argument is that in this scenario, we have introduced an extraneous
metallic part - yes. But that part is earthed by design. I see very little
that can go wrong.

OK - if we were selling this to the general public, one would expect to make
a formalised assessment. However, as always, this is a one off for personal
use. It is of course down to whether the OP feels happy with doing such
stuff (this is a DIY group), but being aware of the cautions given I think
he's got reasonable grounds to make a judgement.

I'm merely presenting the engineering argument "what could go wrong"?

(As I said, I intended the SY flex to connect between the mains supply and a
recepticle in the car - but as we're starting to discuss the case of
modifying a Class II device, then why not - it's interesting.)

If we reduce the argument further, noone should put a plug on a class I
device because they might wire it incorrectly?

I'll just add, this is a "friendly argument" AFAIC as there's no way for you
to deduce that from the tone of my tapping ;-

Cheers

Tim

--
Tim Watts

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