Thanks Rich, that's basically the approach I've been taking, just wanted to determine whether the opto meets reinforced insulation. The UL standard just defines test criteria for double protection not construction requirements that I am used to seeing so that makes it hard to compare to other requirements/standards. The standard doesn't define single protection, I guess the assumption is the rest of the standard applies to single protection. The standard requires the opto be "subjected to 50 discharges from a 0.0005 microfarad capacitor that has been charged to a potential of 20 kV between the short-circuited input and short circuited output terminals." and then pass a breakdown test between input and output to be rated double protection. The only other hint is a definition "Optical isolators employed in some unique audio, video and similar applications bridging reinforced insulation."
The opto OEM has both single and double protection optos in their UL listing file. When I asked them about this they stated "Double protection has independent insulation applied in addition to basic insulation in order to ensure protection against electrical shock in the event of failure of basic insulation." If I assume that is accurate it would seem I would need an opto classified as UL 1577 double protection (if going by the UL approval). I'm waiting to hear back from UL for further clarification and to see if there is any comparison to IEC60747-5-5. -Dave From: Richard Nute [mailto:[email protected]] Sent: Sunday, June 28, 2015 10:15 PM To: Nyffenegger, Dave; [email protected] Subject: RE: [PSES] Optos for PELV isolation Hi Dave: Based on what you have said, I would treat (for safety purposes) the non-PELV as 208 volts. Clearances don't exist within an optocoupler as there is no air within the optocoupler. Likewise, there is no creepage distances within an optocoupler. (Creepage is the interface between solid and air insulation, and since there is no air within the optocoupler there can be no creepage within the coupler.) I don't know what "UL single protection" means. However, since the rated withstand is 5000 volts, one can surmise that the internal insulation is homogeneous solid insulation (i.e., with no air gaps - which would otherwise break down since air is about 3000 volts/mm). If IEC 60664-1 is applied, such solid insulation would qualify for reinforced insulation. If you assume that the non-PELV is 208 volts and the opto is reinforced insulation, then the construction is okay (complies with the requirements of 60664-1). Best regards, Rich From: Nyffenegger, Dave [mailto:[email protected]] Sent: Sunday, June 28, 2015 4:33 PM To: [email protected]; [email protected] Subject: RE: [PSES] Optos for PELV isolation 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 - ---------------------------------------------------------------- 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]>
