Dan, Read on below R9-20 and the requirement is clarified significantly. The requirements are DEFINITELY applicable to the outputs of your DC/DC converters (a.k.a. "embedded DC power supplies"):
If your 48V feeds into a power supply circuit pack/module which then supplies the 3.3, 5, 12, etc... V to the other circuit packs, you must first short the outputs of each individual DC/DC converter (within the common power circuit pack/module) and then (provided you have a passing result from the first test) place shorts on each type of circuit pack that is powered from the common power supply circuit pack/module. (Think of a Compact PCI chassis for an example of this scenario). You must perform the test on each output. If you have your DC/DC converters on each individual circuit pack (most complex telecom type boxes), You must first directly short the outputs of each DC/DC Converter and then move the shorts out to a remote location on the board (Replace a power cap with a short in somewhere on the far corner of the board). This must be done for every type of and each output on the DC/DC modules. Also, if you have DC/DC's of greater than 150W, the outputs are required to be referenced to chassis (R9-9), so you will also need to short the non-referenced side of the outputs to chassis. This test checks the bonding path to ensure that it is sufficient to carry any resulting fault current. The reference path must not be damaged. It should be noted that (contrary to R9-20) many RBOCs do allow damage (damage free is effectively an 'Objective'). They have applied the "fire, fragmentation, or electrical safety hazard" performance criteria to the short circuit test. The product does not necessarily have to function after the test, it just can't catch the cheesecloth on fire or smoke too much (although I've never actually seen a product catch fire, so I haven't looked into this last cheesecloth/smoke bit too much). I hope this helps, Dave Heald -----Original Message----- From: Roman, Dan [mailto:[email protected]] Sent: Thursday, September 12, 2002 8:24 AM To: EMC-pstc List Subject: NEBS - Bonding and Grounding NEBS Gurus, Do the 1089 bonding and grounding DC short circuit tests apply down to the component level in a system or are they limited to the power supply or some other demarcation point? If it applies anywhere in the system it seems to me that you'd never finish testing. You'd have to test the power supply, backplane, mother board, daughter cards, IC dies...sort of like doing the UL 15W test for home entertainment equipment. Reading through section 9 and specifically 9.8 it seems they are keying on the power supplied directly from the CBN and not that power indirectly derived from the CBN after DC to DC converters. Where is the demarcation point if there is one? Do labs that test to NEBS handle this consistently? Thanks in advance. Dan Roman Compliance Engineer Intel ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
