I do not know what "makes sense". LPS requirements are also
defined in several UL safety standards that are based on NEC, for
example, UL1012 ('Limited voltage limited energy') and UL508
('Limited voltage limited current'). In general, the NEC severely
limits allowable materials, external and connected to the power
source, that exceed specific, voltage, current, and/or VA levels.IEC60364 also limits materials that may be used with a power source that exceed certain voltage, current, and/or VA levels. The ability to "pass safety" is dependent on the requirements of the end-use equipment. <Jerk Mode> As all of these limits are clearly and specifically delineated in safety standards, one could assume that the OP has not read the standard, or will not purchase the standard. </Jerk Mode> <Free Advice Mode> It worries me that some regulatory people seem do safety engineering the same way that some design people do software engineering - ad hoc and non-reproducible. For each new model series, whether a component power supply or end-use equipment, I do the following for the design engineer at start of project: 1. using applicable safety stds, I build a list of tables, limits, and construction requirements and link each requirement to a clause. 2. using applicable emc stds, I tabulate a list of emission limits and immunity test levels, and link to the clause in the product family std. 3. I grab a revision 'X1' schematic, do some basic calculations, and red-line the schematic and PCB layout as soon as available. 4. Even if I do not submit test data to an agency or test house, I NEVER send a sample to the safety or EMC labs without performing in-house tests that indicate conformity to all checked clauses that I checked in the applicable CBTR form - so I always know that there is a good margin. 5. When a test house or safety agency rejects my data, or indicates a failed sample, I NEVER accept their requirements or test data at face value. 6. I never accept a passing agency report at face value. I verify that all agency test data will support all applicable clauses in the safety std. 7. When I do HALT at end of design cycle - I consider a test condition that results in the unit not meeting a rating or spacing requirement to be a fail level - it is NOT an operational limit. </Free Advice Mode> From: [email protected] [mailto:[email protected]]On Behalf Of Christine Rodham Sent: Wednesday, January 21, 2009 12:38 PM To: [email protected] Subject: Re: Safety Experts: Limited Voltage Pwr Supplies vs. Non-Limited Voltage Power Supplies List Members, Thanks for all the great replies! Would it make sense to see if the end product can pass safety with the non-LPS power supply? Is the the LPS clause just a CB scheme requirement or is it required for NRTL approval also? Best regards, Christine Rodham Christine Rodham <[email protected]> wrote: Hi List Members, We have a vendor that provides us a unit that uses an external power supply ( 90- 240VAC) The power supply is labeled LPS after the model number which means: Limited Voltage Power Supply. They recently changed vendors to another power supply with the EXACT same rating Except it was not marked as a LIMITED voltage power supply. Our supplier says this is not a compliance / safety issue because both supplies are recognized by UL and have the same voltage and current rating. So the $64,0000 dollar question is can you use a non- LPS in place of a LPS if they have the same rating? Thanks in advance, Thank you in advance! Christine Rodham - 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html 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]>
