Use of shock hazard limits in terms of voltage in product safety standards is already a simplification. See IEC 60479-1 and -2. You can find the free preview of IEC 60479-1 here <https://webstore.iec.ch/preview/info_iec60479-1%7Bed1.0%7Den.pdf>, with a good high level discussion in the scope.
On Mon, Feb 26, 2024 at 2:26 PM Ralph McDiarmid <[email protected]> wrote: > I suspect many of the standards committee have merely adopted the Vpeak > limit from other standards without giving it much thought. Note that > 42.4Vpk is just root2 x 30Vrms. That seems to be all there is to it and I > doubt it’s mere coincidence. (60Vdc/30Vrms/42.4Vpk found in several > standards) > > > > I went back to first principles, did the integration of a d.c pulsed > waveform and then again for an a.c. waveform with same amplitude, same duty > ratio. I found a much higher effective value (RMS) with the a.c. waveform > having sample amplitude and pulse duty ratio. For example, Root2 higher > for 50% duty cycle and Root10 higher for 10% duty cycle. > > > > Now, the NRTL won’t be interested in any of that, but you need to weigh > the intent of the standard versus any other risk analysis might do above > and beyond the “letter of the law” before deciding on whether those > terminals are in fact shock hazardous. It’s your product, your call, your > corporate reputation, so whatever the decision, it needs to be justified > with due diligence. > > > > I would say your power supply output as described satisfies the criteria > of “limit values for accessible parts” as defined in IEC61010 3rd > edition. (33 Vrms, 33xroot2 Vpeak, and 70 Vdc ) A project holder at an > NRTL might disagree. > > > > Ralph > > > > *From:* Richard Nute <[email protected]> > *Sent:* Monday, February 26, 2024 12:08 PM > *To:* [email protected] > *Subject:* Re: [PSES] 61010-1 hazardous live classification > > > > > > Hi James: > > > > In the pulse mode, 46 volts peak exceeds the 42.4 volts peak limit. In > accordance with the 61010 standard, the voltage cannot be accessible in the > pulse mode. > > > > However, the pulse mode is dc (the current does not reverse). The RMS of > such a pulse is 46 times the square root of the duty cycle. The shorter > the duty cycle, the less human sensation of the pulse. Chances are that > the pulse is not detectable by a human finger any more than 60 volts DC. > But the standard does not allow such a determination. > > > > You are stuck. > > > > Best regards, > > Richard Nute > > Bend, Oregon, USA > > > > > > *From:* James Pawson (U3C) <[email protected]> > *Sent:* Monday, February 26, 2024 5:38 AM > *To:* [email protected] > *Subject:* [PSES] 61010-1 hazardous live classification > > > > Hello all, > > > > I hope this safety question is a fairly simple one for you, it being > Monday after all… > > > > 1. A piece of equipment with a power supply output for driving a lamp. > It has two modes, DC and pulsed. > 2. Both of the output voltage connections are on accessible terminals > (checked using finger probe) > 3. Classifying voltages as per EN 61010-1 clause 6.3.1 (limit values > for accessible parts, normal operating conditions) > 4. DC mode runs at 46Vdc maximum. This is less than 60Vdc so is not > Hazardous Live > 5. Pulse mode runs at 46Vdc pulsed (frequency up to 1kHz, duty cycle > can vary down to 0.01%) which is an AC waveform greater than 42.4V peak so > is Hazardous Live > 6. The output from the equipment is low impedance so is more than > capable of sourcing the required 0.7mA through the IEC 60990 body model. > > > > Quick sketch attached to illustrate the concept. I even ran a SPICE > simulation to make sure I wasn’t getting something wrong. > > > > I would appreciate the sanity check! > > > > All the best > > James > > > ------------------------------ > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://ewh.ieee.org/soc/pses/listrules.html For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher: <[email protected]> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
