Hi Folks
The issue I raised - and as supported by Charles Grasso, etc - is not the
the "shock" is an "unpleasant experience", but that the
secondary/consequential effects of the shock can be a "dangerous
experience".
It must be realised that "Joe Public" cannot - and cannot be expected to -
really distinguish between a shock that severely hurts/kills him and one
which just gives him the "unpleasant experience". In his eyes, both were
unexpected and hurt him, and made him unhappy with the equipment and its
supplier (vis Charles' comment). Furthmore, if he is then hurt (say a broken
foot or a very bruised shin)by the secondary reaction effect then he is
going to become even less happy - and maybe start sueing somebody.
Finally, my personal opinion is that:
a) Many of the requirements in most of the safety standards are there to
protect against issues and hypothetical faults and conditions that do rarely
- if ever - actually cause any problems.
[In the types of products (medical products excepted)with which most of us
deal: how many incidents do we really get from inadequate creepage and
clearance distances, from X-ray emissions over the limits stated in the
standards, or from inadequate labelling on the rating plate?];
b) If the injury that can be caused by this type of shock were directly
attributable to the equipment itself (e.g. it traps your foot in it and
breaks it) then the standard would (or at least should) prohibit that
happening as it is a directly foreseeable consquence of a design safety
defect. Therefore any other consequences and directly atttributable similar
levels of effects which are foreseeable from the designer's standpoint, but
with which the equipment user is unlikely to be familiar,should also be
adequately dealt with in the standards. Otherwise the standards-writing
bodies could (and should?) be held responsible for not preparing standards
that address all the relevant hazards from the equipment.
John Allen
Technical Consultant
Electromagnetics, Safety and Reliability Group
ERA Technology Ltd
Cleeve Rd
Leatherhead
Surrey KT22 7SA
Tel: +44 (0) 1372-367025 (Direct)
+44 (0) 1372-367000 (Switchboard)
Fax: +44 (0) 1372-367102 (Fax)
-----Original Message-----
From: Rich Nute [mailto:ri...@sdd.hp.com]
Sent: 20 September 2002 00:00
To: g.grem...@cetest.nl
Cc: emc-p...@majordomo.ieee.org; emc-p...@majordomo.ieee.org;
emc-p...@majordomo.ieee.org; emc-p...@majordomo.ieee.org
Subject: Changing our safety standards (was 0.1 uF discharge)
Hi Gert:
> I also tried the discharge between two fingers, and found the result to
> be unpleasant at least.
> Time to change standards.......
Now we must ask the question:
Is the purpose of the standard to prevent
injury or to prevent an unpleasant experience?
I presume that you would want to adjust the various
values of current (in our standards) so that either
there is no sensation, or the sensations of the
various conditions are the same.
If you try the same test with 3.5 mA leakage
current, I believe you will also find the result
to be unpleasant.
Here's another test:
Using a 2-wire external power supply with a
barrel-type output connector (such as the type
power supply used with a laptop computer), rub
the metal barrel lightly on the inside of your
forearm.
I believe you will find this unpleasant.
Simply, we cannot eliminate the sensation of
electric current -- from an ac voltage source --
through a capacitance. Somewhere, someone will
sense the current. We *may* be able to eliminate
the sensation of electric current from a charged
capacitor by selecting small-value capacitors.
But, is that the purpose of our safety standards --
to eliminate sensation of electric current? What
should be the body response criterion used in
safety standards?
Best regards,
Rich
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