Alex, 1. What is the correct method to test for a Limited Power source in determining what enclosure is required?
Peter: The correct method for inherently limited power source is to measure the output current (Isc) after 60 seconds of operation with the load adjusted to maintain the Isc current limit (8.0 A). In your case the PTC serves as the impedance limiting the current flow. I do not understand why the Isc (8A load) lab failed you since you did not exceed the 8A and the result should have been acceptable. 2. If a fire enclosure was needed what is the minimum plastic rating i.e. 94V0, V1 or what? Peter: Sounds like you have a movable equipment with a total mass < 18 kg. For a fire enclosure, you need a 94V-1 enclosure or one that can withstsnd the tests of Clause A.2 3. I cannot put a 5A fuse in the product, the lab says that the overcurrent protective device must be outwith the non-fire enclosure in order to stop the non compliant energy source entering the enclosure. Is this correct? Peter: I assume you mean you cannot put a max. 5 A or less to meet the Isc of less than or = 1000/Uoc for power sources not inherently limited. The rated current values of the overcurrent protector in Table 9 are for devices located in the secondary. If the fuse is located in the primary, the max values of Table 9 should be adjusted based on the pri/sec windings turns ratio. For example, if a transformer has a 5:1 turns ratio, then the max values of the rated currents for the overcurrent devices in the primary should be adjusted to 1/5 of the values shown, or in your case 1/5 (5 A) = 1 A The fuse and transformer must be within the fire enclosure. You can get away with it if your fuse is within an appliance inlet in the primary, your leads are PVC, TFE, PTFE, FEP or neoprene and the transformer itself (except laminations) has its own fire enclosure. There are many transformer constructions with bobbin/cover constructions which would meet the fire enclosure requirements. For reference, see 4.7.2.1 (parts requiring fire enclosures) and 4.7.2.2 (parts not requiring fire enclosures). 4. Similarly, I cannot use a resettable fuse in the product to meet these requirements? Peter: You have a PTC within the transformer; make sure it is approved and meets the tests in IEC 60730-1, clauses 15, 17, J15 and J17. 5. Does the PTC used in the power supply need to meet the IEC 60730-1? Peter: Only the parts specified above. Summary: It seems you wish to use a cheap enclosure material (94HB). Get a fused applied inlet. Install a fuse value based on the transformer pri/sec turns ratio as mentioned above. Use a transformer with a 94V-1 fire enclosure over the windings and make sure its' wires are PVC, TFE, PTFE, FEP or neoprene. With the fuse bypassed, make sure you meet the limit for Isc (A) and S (VA) in Table 9 in the standard. You are all set and ready. This e-mail message may contain privileged or confidential information. If you are not the intended recipient, you may not disclose, use, disseminate, distribute, copy or rely upon this message or attachment in any way. If you received this e-mail message in error, please return by forwarding the message and its attachments to the sender. PETER S. MERGUERIAN Technical Director I.T.L. (Product Testing) Ltd. 26 Hacharoshet St., POB 211 Or Yehuda 60251, Israel Tel: + 972-(0)3-5339022 Fax: + 972-(0)3-5339019 Mobile: + 972-(0)54-838175 http://www.itl.co.il http://www.i-spec.com -----Original Message----- From: Alex McNeil [mailto:alex.mcn...@ingenicofortronic.com] Sent: Friday, August 30, 2002 11:25 AM To: 'emc-p...@majordomo.ieee.org' Subject: EN60950-1 Sect 2.5 Limited Power sources Hi group, I have a query on the understanding of the above section. I thought I fully understood it until I used a different lab for Product Safety Compliance testing (both accredited!). We use a linear (basically a transformer with a PTC thermistor) class II SELV O/P stand alone power supply rated 10Vac, 5A. One of the labs tested the O/P Isc with a direct application of the sc. The other lab tested the O/P Isc by applying a load of 8A. The results were therefore interpreted differently. Isc (direct) = 30A falling to 0A within 30secs. Considered a PASS (8A for < 1min) Isc (8A load) = 8A for > 2mins. Considered a FAIL (8A > 1min) This has a crucial bearing on whether I need a fire enclosure or not for my all plastic enclosure! 1. What is the correct method to test for a Limited Power source in determining what enclosure is required? 2. If a fire enclosure was needed what is the minimum plastic rating i.e. 94V0, V1 or what? 3. I cannot put a 5A fuse in the product, the lab says that the overcurrent protective device must be outwith the non-fire enclosure in order to stop the non compliant energy source entering the enclosure. Is this correct? 4. Similarly, I cannot use a resettable fuse in the product to meet these requirements? 5. Does the PTC used in the power supply need to meet the IEC 60730-1? I would very much appreciate clarification on this matter. THANKS!! Kind Regards Alex McNeil Principal Engineer Tel: +44 (0)131 479 8375 Fax: +44 (0)131 479 8321 email: alex.mcn...@ingenicofortronic.com ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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