Regarding Case 1 (and any other where voltages do not exceed the limits in 6.3.1/6.3.2), it may be simpler to apply the fault testing in 9.1a)2) rather than apply Basic Insulation. Of course a wrinkle would be if your unlimited low voltage circuit is accessible, requiring you to deal with the fire hazard in any external equipment the circuit could be connected to (and possibly needing additional fault testing). If you do go for Basic Insulation, then it seems that table 5 should be used for clearance per 6.7.3.1a), since none of the exceptions in 6.7.3.1b) seem to apply. Of course that table starts out at 50V. I would use the 50V value from column 3 - 0.53mm.
Case 2 - seems about the same as Case 1, though you haven't specified the secondary voltage. Case 3 - Regarding separation from the output of the inverter and its 5V supply, I'm not sure that spacings are required here. Is the 5V accessible? What happens if the output of the inverter is shorted to the input - are hazardous voltages per 6.3.1 accessible for any length of time? Regarding clearances from the output of the inverter to other circuits, the same basic rules apply as for Cases 1 and 2 - table 5 would be the correct choice unless any of the exceptions in 6.7.3.1b) apply. Assuming the mains voltage to the transformer with the 5V secondary is 230V and OV cat II, then column 3 of table 5 would be appropriate. Scott Aldous Compliance Engineer Advanced Energy Tel: 970-407-6872 Fax: 970-407-5872 From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of iun...@servomex.com Sent: Tuesday, November 13, 2007 3:49 AM To: emc-p...@ieee.org Subject: EN 61010-1 - Clearances Dear All, I have three questions regarding the calculation of clearances in accordance with the requirements of EN 61010-1. Can anybody out there help please? Case 1 - Mains input transformer (230 Vac rms, Over-voltage category 2) supplies an ac to dc converter providing +15 Vdc output (not energy limited). To generate an energy limited supply, an appropriately approved PCB (Pollution degree 1, CTA> 175) mounted current limiting device is fitted in series with the dc supply. How do I determine the clearances around the unlimited +15 Vdc supply and the current limiting device? Which of the tables included in EN 61010-1 are appropriate and why? Case 2 - PCB mounted mains transformer (230 Vac rms, Over voltage category 2) is protected by an appropriately approved PCB mounted current limiting device in series with the secondary windings. How do I determine the clearance distances around the tracks from the secondary winding up to the current limiting device? Which of the tables included in EN 61010-1 are appropriate and why? Case 3 - I am looking at designing a push-pull inverter powered by a 5 Vdc supply derived from a mains transformer. What are the EN 61010-1 rules governing the clearances around the outputs from this inverter and the separation of the 5 V dc input and ac output circuits? Many thanks in anticipation of your help. Ian Unwin Servomex Group Limited, Jarvis Brook, Crowborough, East Sussex, TN6 3DU, England. e-mail: i...@servomex.com Company Registered in England: No.2170458 VAT No.: GB 522 6077 63 Register now at http://www.servomex.com/zap.html for an opportunity to win a great prize in our quarterly draw. 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