Hi Rich, Thanks for the feedback. In the application I have in mind the non-PELV is nominal 24VDC. Obviously this voltage is within PELV limits however the cabling for this application is such the 24VDC circuit runs along with 208VAC, sharing the same connectors and wire troughs and physical separation is not practical. There is only basic insulation on both 208VAC and 24VDC wiring and the connectors do not have any special insulation ratings between contacts. I'm not sure if the basic insulation on the 208V together with the basic insulation on the 24V wiring would meet the requirement of maintaining a PELV voltage in the event of a single fault on one of the basic insulations or not. I'm even less sure of the ability of a single fault in the connector housing to maintain PELV voltage. The source of the 24VDC is a transformer and I've not confirmed if it meets the requirements for safety isolating transformer. This is an existing application being reviewed and I'm going on the assumption that the 24VDC circuit is not PELV.
The 24VDC circuit does not need to be PELV by itself however it interfaces to a PELV circuit via an existing optocoupler. Physical clearances on the PCB layout and optocoupler pins are greater than 3.0mm so no concerns there. The only component in question is the internals of the optocoupler itself. The opto data sheet does not publish internal clearance specs on the opto, only that it is UL 1577 approved for single protection and the input/output isolation voltage is min 5000V @60sec. So it would seem the opto meets the voltage requirements of IEC 60664-1. I'm just not clear if the UL single protection rating is sufficient for this application. If it takes a single fault to get 208V on the opto and a second fault at the opto to get hazardous voltage to the PELV side then perhaps the opto is OK as is in this application. The opto is also available with an IEC60747-5-5 rating with VDE mark as an option. The OEM says the only difference with these optos is an additional non-destructive production line voltage test on each opto. -Dave From: Richard Nute [mailto:[email protected]] Sent: Sunday, June 28, 2015 6:36 PM To: Nyffenegger, Dave; [email protected] Subject: RE: [PSES] Optos for PELV isolation Hi Dave: The optocoupler must be rated for the voltage across the optocoupler. If the high voltage side is subject to transient overvoltages, then the optocoupler must be rated to withstand the transient overvoltages. IEC 60664-1 defines transient withstand voltages for mains circuits. If the high voltage side is 120 volts, then the withstand must be 1500 volts peak. If 220, 230, or 240 volts, the withstand must be 2500 volts peak. If the optocoupler is required to be reinforced (or double) insulation (and it most likely is), then the withstand voltages are 2500 volts peak and 4000 volts peak. The clearance across the optocoupler must be at least 0.5 mm for basic insulation and 1.5 mm for reinforced insulation for 120 volts. Clearance must be at least 1.5 mm for basic insulation and 3.0 mm for reinforced insulation for 220-230-240 volts. (Creepage cannot be less than clearance). These numbers may not be the same as specified in 60204, 61558, 60747, or UL 1577 (but they are close). IEC 60664-1 is the basic safety standard which all other standards must use. Not all standards committees have followed this rule, nor have they necessarily understood IEC 60664 series. Good luck, and best regards, Rich From: Nyffenegger, Dave [mailto:[email protected]] Sent: Friday, June 26, 2015 10:50 AM To: [email protected] Subject: [PSES] Optos for PELV isolation Hi Folks, I'm trying to determine the appropriate ratings for optocouplers to meet PELV isolation requirements from non-PELV low voltage circuits. EN 60204-1:2006+A1:2009 6.4.1 c states "live parts of PELV circuits shall be electrically separated from other live circuits. Electrical separation shall be not less than that required between the primary and secondary circuits of a safety isolating transformer (see IEC 61558-1 and IEC 61558-2-6 );" The IEC 61558 standards are written for transformers and I'm not sure how that translates into specifications available for optos or to UL 1577 or EN/IEC60747-5-5 that some optos are approved to. I have seen UL reports testing optos to UL 1577 "single protection" or and "double protection" isolators. UL 1577 itself doesn't clearly define "single" and "double protection" and I'm currently waiting to hear back from UL on that. I am using optos to switch on a non-PELV circuit from a PELV circuit. Does anyone know if optos approved to UL 1577 Single protection and/or Double protection and/or EN/IEC60747-5-5 meet the EN 60204-1 requirements for PELV isolation from non-PELV circuits? Thanks -Dave David P. Nyffenegger, PMP, SM-IEEE Product Development Manager Bell and Howell 3791 South Alston Avenue Durham, NC 27713 Phone: 919.767.6419 Web: www.bellhowell.net<http://www.bellhowell.net/> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
