I can see one reason for a capacitance limit AND a current limit. Consider two sets of terminals with identical peak current specifications. However, one set of terminals has internal capacitance such that it will remain charged and capable of that peak current much longer after the product has been turned off.
In my mind, the second set of terminals are more hazardous because many users may start thinking that the hazard has cleared, once the product has been turned off. These users could get quite a surprise! So, specification of a current limit and capacitance limit set both a limit on how much current can be delivered by terminals and a limit on how long after turnoff this current could still be delivered. I can't read the minds of the standards bodies (I'm not really sure if I'd want to)...so I'm not sure if this reasoning is correct. But it does stand to some logic. However, with the exception of Leonard Nimoy...we all know that logic doesn't always rule. Chris Maxwell, M.Sc Electrical Engineer Critical Imaging LLC www.criticalimaging.net > That is my take on it, why impose a capacitance limit at all if you > already limit the current. But I think perhaps I'm missing the intent of > the capacitance limit. > > In my wishes, and I do mean wishes, I could fail the 7uA limit, and meet > the capacitance and thus be a limited current circuit. > > ________________________________ > > From: [email protected] on behalf of Ralph McDiarmid > Sent: Thu 11/2/2006 12:44 PM > To: [email protected] > Subject: RE: 60950 question > > > > If you meet the peak current limit, wouldn't you also meet the > capacitance limit by necessity? > > Ralph McDiarmid, AScT > Compliance Engineering Group > Xantrex Technology Inc. > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of Kim Boll > Jensen > Sent: Thursday, November 02, 2006 2:21 AM > To: Clif Brick; [email protected] > Subject: SV: RE: 60950 question > > Hi > > First part of 2.4.2 talks about frequency (over OR under 1 kHz) next > part > talks about voltage (over OR under 450 Vac) so it must be an AND between > those two requirements (current limit AND Capacitance). This is how CSA > told > me about the requirements 8 yeasr ago. > > Best regards, > > Kim Boll Jensen > Bolls Radgivning > Ved Gadekaret 11F > DK-3660 Stenlose > > Tlf.: 48 18 35 66 > Fax: 48 18 35 30 > Mobil: 22 99 69 91 > > E-mail: [email protected] > web: www.bolls.dk > > -----Oprindelig meddelelse----- > Fra: [email protected] [mailto:[email protected]]Pa vegne af Clif Brick > Sendt: 1. november 2006 17:41 > Til: [email protected] > Emne: [Norton AntiSpam] RE: 60950 question > > > John, > > In this case, I'm not sure that 'and' makes sense. If it were 'and', > then one would need to be certain, in spite of having a result lower > than .7mA, that the circuit capacitance met the additional requirements. > That isn't standard practice as far as I'm aware. > > There is a great difference between a sinusoidal, continuous current > that exceeds let go and a current that MUST end due to lack of capacity > or stored energy. > > In the sense of IEC 479-2, I think it's pretty clear that OR would make > sense here, as there wouldn't be enough energy to cause burns, not a > long enough current to exceed let go, and not a waveform likely to cause > fibrillation. > > I don't know, I'm just trying to learn. > > Thanks, > > Clif > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of John > Woodgate > Sent: Wednesday, November 01, 2006 10:43 AM > To: [email protected] > Subject: Re: 60950 question > > In message > <4be0b2b96f73e3448c6f86309fc15ca605ac5...@iticpm01.innotek-inc.com>, > dated Wed, 1 Nov 2006, Clif Brick <[email protected]> writes > >>My question is one of understanding whether or not I must AND or OR the > >>seperate clauses in 2.4.2. > > This is a problem that keeps coming up in many standards. Editing > committees should take careful note of it. It is worse with bulleted > lists, which can be totally ambiguous with respect to 'AND' or 'OR'. But > in the plain text of 2.4.2, one has to assume that the requirements are > 'AND'. > > What does the Annex D measurement give as a result? If you don't have > the instrument, you can do a SPICE simulation. > -- > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk > Swine wave - a waveform whose spectrum is exceptionally difficult to > calculate. > John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. 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