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Standards for a PSU to be considered as "SELV"

Tim Watts
Hi - quick standards question, for hobby purposes only:


Is a declaration of being "Class II" and within the appropriate voltage band, sufficient for a PSU to be considered as SELV for usage scenarios in BS7671?


I'm doing a Raspberry Pi project with my son to PWM drive some 30V LED outdoor fairly lights. So I'm choosing a PSU that's nice and safe.


The candidate PSU I have is this one: 30V PSU (RS) or possibly this one 30V PSU (-10C) for it's lower operating temperature (it's going to be in the shed, occasional drops below 0C possible)


First one is defined as Class II, it's 30V. It also claims medical approval. A whole bunch of quoted standards on the datasheet above. Apart from "Class II", not sure if I should be looking at any particular standard that defines it as meeting SELV PSU requirements. Isolation voltage is given as 4kV?


Second one claims very little but implies Class II by lack of protective conductor pin.


Pretty sure either is a good choice (noting operating temperature limits of the first), but academically I have been curious what defines a SELV PSU if it doesn't actually have the word SELV printed on it?


Many thanks as always for letting me tap the font of knowledge that this forum is :)


Tim


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  • 0
    This issue is set to become more "nebulous".


    BS EN 60950-1 is sometimes used for switch-mode power supplies. It is being replaced by BS EN 62368-1 (which is also replacing BS EN 60065), and the new standard will be in full force in 2020 I understand.


    Now, BS EN 62368-1 does NOT recognise SELV and PELV, and it is not at all clear whether, under all fault conditions conditions, the output of a supply to BS EN 62368-1 might be guaranteed to be "just as safe" as a safety isolating transformer.


    Now, of course a manufacturer that made an SELV (or PELV) supply under BS EN 60950-1 could continue to do so, probably without design change, and certify it to BS EN 62368-1, BUT the important point for those specifying sources for SELV and PELV is that, just by virtue of the product complying with BS EN 62368-1 does not mean you're getting an SELV (or PELV) supply that we used to assume we were getting.


    Would a product only conforming to BS EN 62368-1 (but not BS EN 60950-1) comply with BS 7671 as a source for SELV/PELV?


    Well, possibly it could be argued to be a source according to 414.3 (iv), and is likely to be fine in dry conditions. But I'm not, at present, 100 % sure  (without further investigation) that, under all fault conditions in situations it would protect a person we are trying to protect against shock would be substantially wet / submerged, and unclothed, in the same manner as an SELV/PELV source to 414.3 (i), (ii) or (iii).
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  • 0
    This issue is set to become more "nebulous".


    BS EN 60950-1 is sometimes used for switch-mode power supplies. It is being replaced by BS EN 62368-1 (which is also replacing BS EN 60065), and the new standard will be in full force in 2020 I understand.


    Now, BS EN 62368-1 does NOT recognise SELV and PELV, and it is not at all clear whether, under all fault conditions conditions, the output of a supply to BS EN 62368-1 might be guaranteed to be "just as safe" as a safety isolating transformer.


    Now, of course a manufacturer that made an SELV (or PELV) supply under BS EN 60950-1 could continue to do so, probably without design change, and certify it to BS EN 62368-1, BUT the important point for those specifying sources for SELV and PELV is that, just by virtue of the product complying with BS EN 62368-1 does not mean you're getting an SELV (or PELV) supply that we used to assume we were getting.


    Would a product only conforming to BS EN 62368-1 (but not BS EN 60950-1) comply with BS 7671 as a source for SELV/PELV?


    Well, possibly it could be argued to be a source according to 414.3 (iv), and is likely to be fine in dry conditions. But I'm not, at present, 100 % sure  (without further investigation) that, under all fault conditions in situations it would protect a person we are trying to protect against shock would be substantially wet / submerged, and unclothed, in the same manner as an SELV/PELV source to 414.3 (i), (ii) or (iii).
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