I believe that Juan has a legitimate gripe. Standards are written by
subcommitties and working groups whose agendas, biases or professional
viewpoints can color the process. Sometimes one standard is intended
to be a relaxed version of a more comprehensive document. EN 61010
(electrical safety for laboratory instruments) is case in point.
'1010 appears to be a relaxed edition of IEC 950 or EN 60950. The
easing of requirements exists because the equipment operators are
assumed to be knowledgeable persons who are unlikely to KNOWINGLY do
something life-threatening. The requirements are also eased because
laboratory equipment sometimes needs to generate dangerous conditions
in order to perform its intended function (e.g., transient surge
generators).
Sometimes the relaxation goes too far, or the people making the
changes don't reckon with the cultural biases of some of the users or
safety agency personnel.
My particular peeve is that the concept of "operational insulation"
contained in IEC 380/435/950 and EN60950 is altogether lacking in
EN61010. This means that the least-safe insulation category in
EN61010 is basic insulation. Operational insulation is defined as
that "insulation needed for the correct operation of the equipment".
Basic insulation is defined by '950 and '1010 as insulation to
provide basic protection against electrical shock. The concept of
operational insulation was devised to accomodate those situations in
which no shock hazard exists (e.g., circuits within a closed, earthed
metal container) where there was no need for the thicker insulation
that would guarantee safety against electrical shock to homo sapiens.
I have had several arguments with safety examiners regarding
compliance with EN61010 in cases where operational insulation is all
that is required -- cases in which no human access is possible, where
if insulation breakdown occurs, the equipment fails and just stops
working. It does not catch fire. No harm to humans results from
this breakdown. The examiners take the stance that since operational
insulation is not addressed by '1010, the most rudimentary form of
insulation must be basic insulation. This adds bulk to the wiring
and clearance/creepage burdens to the other components. It is, I
reason, an unjustified rationalization of an oversight in the
standard. Rather than use common sense and working the issue, the
examiners are taking the position that if it doesn't say you MAY do
such-and-such --- then you are forbidden to do it.
I'd appreciate some feedback on this particular example. It's not
the first time that I've felt jerked around by an agency taking what
amounts to an arbitrary position on conditions not covered by the
standard.
Juan's plea for a single safety standard may not be achieveable, but
certainly coordination between standards groups and harmonization of
standards could be improved.
PAG
______________________________ Forward Header __________________________________
Subject: One safety standard?!
Author: =?iso-8859-1?Q?Juan_Pedro_Pe=F1a?= <[email protected]> at Internet
List-Post: [email protected]
Date: 9/27/96 08:24
Hello everybody (from Malaga)!
Thank you for your comments, particularly to Rich Nute for his clear exposition.
I have seen the argumentation about IEC 601. I did not include IEC 601 because
it is the standard
in which, perhaps, I better understand the differences. But, of course, you can
write IEC 601 like
IEC 950 + complements, though the complementary standard should be rather large.
However, I could include many other standard I didn't for simplification
reasons. For example, the
standards considered of electrical appliances (not electronic) like IEC 335.
Long time ago,
electrical and electronic appliance was absolutely separated. That is not true
at this moment.
Electronic is included in almost all the appliances and you can find motors and
other electrical
components in many electronic appliances. One example of the mixture is the
electronic insects
killer (IEC 335-2-59), included in the scope of IEC 335 although it is an
electronic appliance.
However, normalization committees are absolutely separated. The result is
different tests to check
the same requirements (putting out particular requirements).
We could speak about many other standards like IEC 924, IEC 928, IEC 730, IEC
215, IEC 1046, etc.
But my main problem is to find justification to the differences. Let me go back
to flammability
requirements. Rich is right, abnormal conditions are checked in each standard
then, you can get some
warranties about the fire risk. However, description of how to test abnormal
conditions are much more
extensive in IEC 950 than in other standards. So, some one can infer that
flammability requirements in IEC
950 could be weaker. But it is the opposite. For one equipment on the border
between IEC 950 and IEC 65,
supposed it pass all abnormal tests, if IEC 950 is applied, the manufacturer has
to used good and expensive
plastic materials (minimum HB class, V1 for fire enclosure). But if IEC 65 is
applied, the manufacturer can
save a good money in plastic quality. In my position like a testing laboratory,
it is difficult to explain to my
clients so big difference.
In the future, I will put in your consideration some other important differences
between standards with
difficult justification. I hope that normalization committees read and answer.
Thank for your comments.
========================================================
Juan P. Pena / Electrical Safety Area
Company: CETECOM, S.A. (http://www.pta.es/ing/empresas/cetecom.html)
e-mail: [email protected]
The opinions expressed are personal, not necessarily of my company.
========================================================
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