Many line filters do indeed have a bleeder resistor built in. There
are a few which do not, and I am familiar with one Delta filter that
does not. We added the bleeder across the terminals of the filter and
it was approved by UL. It just has to be done in accordance with
accepted construction practices.
This particular filter is and IEC plug type so the leads are not
saliently exposed unless the cord is left attached. None the less I
agree with John that it is not a good idea to ignore because one
instance will get you a lot of word-of-mouth bad press and sales are
hard-enough to come by so to speak.
Warren Birmingham
Epsilon-Mu Consultants
(510) 793-4806
email: war...@epsilon-mu.com
website: http://www.epsilon-mu.com
On Wednesday, Sep 18, 2002, at 10:11 US/Pacific, John Allen wrote:
Hello Folks
Tomonori Sato commented "However, I think discharge from 0.1uF
capacitor charged to the mains peak voltage can be quite
uncomfortable."
I believe that to be true from personal experience and from having to
investigate the results of a number of such incidents, and so would
remind member of a point that I made several years ago on this forum:
The primary shock almost certainly will NOT hurt a person, but the
involuntary reaction TO the shock may well have much more
seriousconsequences.
This type of shock is often encountered by people who pick up
equipment which they have just unplugged from the AC mains in order to
carry it elsewhere. If they then touch the pins of the plug there are
numerous reported incidences of them involuntarily dropping the unit -
and that can possibly be on their own feet - and from a height of
about 3ft/1m! If the unit is more than a couple of pounds (about one
kilo) then the injury to t! he feet can be substantial.
Worse situations could occur in industrial equipment when a service
engineer opens a cabinet to perform a service operation - the reaction
from the "shock" could cause him to strike touch other hazardous
electrical or mechanical parts (which probably should also not be
there, I do agree!) which then cause him serious actual injury.
These types of incident do not make the equipment supplier very
"popular" to say the least, and could result in product liability
claims.
The main basis for the claims would be that the supplier had not
adequately assessed the hazards and taken the appropriate simple
precautions which are easily and cheaply available - fit a bleeder
resistor across the capacitor, or use a filter with a resistor already
built in (or with transformer/inductor windings directly across the
capacitor - which achieve the same result) !
Again from personal experience I can say that it is a very
"embarassing" and un! comfortable experience to have to write to an
injured or anno! yed person, or to his employer, to say "sorry, but
that is what the safety standard allows". It is just not good
"business sense".
Therefore, regardless of the requirements of the various standards and
this argument over capacitor value and/or charging voltage, I firmly
believe that the use of bleeder resistors should be considered
effectively mandatory, and have always recommended it to engineers I
have advised on product safety.
Regards
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)
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Replies to this message may be posted in the following public forum:
Question: Discharge capacitance 0.1 uF
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