Andy, the problem with 900A is while it destroys the fuse and traces, it creates enough plasma to blow the ultrasonic weld wide open. and even if you will use 32A breaker for backup protection, the event is so fast (2-3ms) it will be all over by the time it reaches the breaker. It usually happens on the first half cycle. Mark
________________________________ From: [email protected] To: [email protected] Subject: RE: [PSES] IEC 60950-1 short circuit test criteria List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Tue, 19 May 2009 09:15:21 +0100 Hi For Direct Plug-In, or Pluggable equipment it is ok to rely on the installation fuse and crucially the installation instructions must state the specifications. The test is performed assuming the installation fuse is as specified. Clause 5.3.1 states that it is permissible to use fuses etc and the approach to testing would be to verify that the specified fuse does operate and that the fuse is an appropriately approved type. The short circuit test current would be the maximum that the fuse would allow without operating – this value would specified in the fuse testing specification; i.e. for miniature fuses IEC 60127 etc. The test is then performed with the protecting fuse short circuited. The breaking capacity of an installation fuse would not be considered as this is dealt with by the installation, not the EUT. If protection is relied upon by a fuse internal to a EUT designed for domestic use, one has to assume there is a limit to the available current; and it would be assumed that an appropriately approved miniature fuse has sufficient breaking capacity for the domestic supply. The highest current domestic circuits are usually 30A in the UK and a 30A supply would probably be used for the short circuit test. Note that using a 900A supply may actually be a less severe test, since the EUT would probably disintegrate and open circuit before temperatures had chance to rise! For welded constructions the EUT would normally be cut open, thermocouples fixed and then the enclosure sealed with tape. You are allowed however to perform the test in the open in certain circumstances, for example if on analysing the circuit and protection, if it seems that a protection device will operate quickly, and temperatures are not likely to get close to the compliance limits. This is a normal procedure, especially when there are several tests to perform. If results indicate otherwise, then a more realistic test can be performed later. A good test lab will normally use engineering judgement, rather than blindly do tests. This reduces the amount of testing time, and destroyed samples, and also produces a better result. See www.ukas.org <http://www.ukas.org/> forUK accredited labs. There are other labs that can do these tests more cheaply and not necessarily to a lower standard. Conformance Ltd can test many products using qualified and experienced engineers, but we are not accredited and only have a 30A supply. Andy Clifford Conformance Ltd - Product safety, approvals and CE-marking consultants The Old Methodist Chapel, Great Hucklow, Buxton, SK17 8RG England Tel. +44 1298 873800, Fax. +44 1298 873801, www.conformance.co.uk Registered in England, Company No. 3478646 ________________________________ From: Mark Gandler [mailto:[email protected]] Sent: 19 May 2009 01:14 To: [email protected] Subject: [PSES] IEC 60950-1 short circuit test criteria Hi, I would like to get your opinion on the test conditions applicable for sections 2.7 and 5.3, primarily for short circuit test. Let's assume it is direct plug-in equipment/AC-DC power adapter. What will be most appropriate power source requirement for performing s.c. test for UK ring? I can find the source which can go as high as 900A while shorted on the primary side and can adjust the phase (which we found at 0 degrees it has the highest effect). Assuming product is going to relay on building installation for backup protection. I would like to get opinions and examples on what would be considered optimum and worst case scenarios. Do you think it is reasonable to expect lab in China or US could adequately represent real life conditions let's say of the power ring in UK? We observed failures just by plugging in short circuited equipment in the standard outlet which could not be reproduced in the lab. what is the common practice for abnormal testing for ultrasoncly welded adapters? do you cut a window then reaseal it, do you test just open PCB? what is the typical circuit breaker in UK? 32A? does every outlet has build in 13A fuse? Last but not the least question: could you please recommend reliable brand name 60950 Safety Lab in UK? (would not hurt if near London)? Thanks a lot for any advise Mark Gandler ________________________________ Windows Live™: Keep your life in sync. 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