Joe, Short-Circuit Tests NOTE: The short-circuit tests that follow are intended to be performed only on out-of-service equipment. NOTE: Discrete equipment assemblies that have been listed by an NRTL to UL 60950[31] generally need not be subjected to the short circuit tests in Section 9.10.1 and Section 9.10.2 and are considered compliant with this section. However, if the EUT has a DC or AC power source rated at >20 VA which would not be required to be tested as part of the NRTL listing program, it shall be tested as described in Section 9.10.1 and Section 9.10.2 as appropriate. 9.10.1 DC Power Sources R9-27 [92] Except as noted below, at least one short-circuit test shall be performed on each type of dc power source having a rated power rating of greater than twenty (20) VA associated with the network equipment. Typical types of dc supplies are rectifiers, rectifiers and associated battery, and dc-to-dc converters. The short circuit test need not be applied for a source consisting of a battery or a string of batteries that is not equipped with an overcurrent protective device. If the output of a rectifier or similar source is normally connected in parallel with batteries, the batteries shall be disconnected during the fault current tests on this source. The short-circuit tests need not be applied for a source that solely provides power to a single telecommunications port if an equivalent short-circuit would be performed in accordance with Section 4.6.5. These tests shall verify that the fault-current path will safely conduct the fault current resulting from the short circuit, and in the case of power supplies required to be grounded (R9-9 [79]), shall verify that the supplies are solidly grounded. For ungrounded power supplies, the short circuit shall be initiated between the positive and negative output terminals. The short circuit shall first be initiated at the power supply output terminals, and repeated at the load if the load is remote from the power supply output terminals. For grounded power supplies, short circuits shall be initiated between the ungrounded side of the source and the return conductor, and between the ungrounded side of the source and the metalwork of the enclosure. Suggested points to initiate the short circuits are at points on the output circuit that are farthest from the source and downstream from over-current devices intended to protect equipment and wiring. Short-circuit tests shall be applied to embedded dc power supplies that are mounted on (on-board) and intended to power individual circuit packs, as well as to supplies intended to power a complete shelf or rack of circuit packs. For onboard power supplies, the short circuit shall first be applied at the power supply output terminals, and repeated downstream (within the circuit pack) from the power supply output to ensure that printed wiring paths and components will not be damaged or become a fire hazard. A representative sample of test points shall be chosen to cover variations in wiring path lengths and affected components. Where the architecture includes a separate power supply for an entire shelf or rack of circuit packs, the short shall first be applied at the output terminals of the power supply, and repeated at a point within the individual circuit pack(s) being powered. If there are a number of circuit pack types or configurations, then a representative sample of each type or configuration shall be tested. For both grounded and ungrounded power supplies, conformance to this requirement shall be demonstrated by the following conditions. The EUT shall not become a fire, fragmentation, or electrical safety hazard as described in Section 4. There shall be no damage to any component of the fault current path. The circuit pack, module, or sub-assembly where the short-circuit is applied, including any power supplies within the unit assembly, need not be in full working order after the short-circuit is removed. Damage to other circuit cards, modules, and subassemblies within the unit assembly shall not occur. Damage to other equipment or wiring shall not occur. Fuse replacement is permitted. A power supply that supplies multiple units shall be restorable by operator intervention (e.g. fuse replacement) after the removal of the short-circuit, except where the short is applied upstream of the protective circuit for the power supply. Each short circuit shall be applied for one minute. When the supply ceases delivering current (e.g., overcurrent protection operates) the short circuit can be removed. If, after one minute, the supply continues to deliver non-negligible (>1A) current into the short circuit, the short circuit shall be maintained until the current ceases or for 15 minutes, whichever occurs first. If the circuit is interrupted by opening of a component other than a NRTL listed or recognized fuse, the test shall be repeated twice using new components as necessary.
Compiled from Issue 3 GR-1089 Alain Servais Compliance Engineer -----Original Message----- From: j...@aol.com [mailto:j...@aol.com] Sent: Monday, November 25, 2002 1:25 PM To: emc-p...@majordomo.ieee.org; t...@world.std.com Subject: Short circuit tests in GR-1089 << File: Short circuit tests in GR-1089.TXT >> Hello All: I am hoping that some of you can help clarify the intent of requirement R9-20 in Telcordia GR-1089. Taken literally, the requirement says that there shall be no damage to equipment, conductors, or components when the DC power supply is shorted at the load. This could even be interpreted to preclude the use of a fuse that has to be replaced. One test lab has told me that as long as no fire hazard is created from this test, it is considered to have been passed. Needless to say, this differs a bit from the literal interpretation. I guess it would help if I had a better feel for the overall goal of the short circuit testing. Any insight on this would be most appreciated. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com ============================================================ The information contained in this message may be privileged and confidential and protected from disclosure. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that any reproduction, dissemination or distribution of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by replying to the message and deleting it from your computer. Thank you. Tellabs ============================================================ ------------------------------------------- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
