Hi All,
>From personal experience I can tell you that the involuntary reaction to a shock can have serious consequences to the sales of a company. In a former life - a previous employer OEM'd a PC from a Korean Company. The PC had all the relevant marks but somehow the resistor that was supposed to bleed off the caps didn't make it into production. A customer , moving said model from one location to another, touched the mains terminals and felt a shock. The customer fell over, the PC landed on the customer, the customer sued and the story ended up in the papers. The sales of PCs essentially died after that. - All for the sake of one resistor. Best Regards Charles Grasso Senior Compliance Engineer Echostar Communications Corp. Tel: 303-706-5467 Fax: 303-799-6222 Cell: 303-204-2974 Email: charles.gra...@echostar.com; <mailto:charles.gra...@echostar.com; %20> Email Alternate: chasgra...@ieee.org <mailto:chasgra...@ieee.org> -----Original Message----- From: John Allen [mailto:john.al...@era.co.uk] Sent: Wednesday, September 18, 2002 11:11 AM To: emc-p...@majordomo.ieee.org Subject: Question: Discharge capacitance 0.1 uF 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) ---------------------------------------------------------------------- Replies to this message may be posted in the following public forum: Question: <http://ieeepstc.mindcruiser.com/direct/topic/a/ID509830> Discharge capacitance 0.1 uF
