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Common Systems Connection Standards AT&T Services, Inc
Date: August 31, 2007 ATT-TP-76450, Issue 9
Copyright ©2004 – 2006, AT&T Knowledge Ventures
All rights reserved
Page 5
2 DC Power Interconnection Standards
2.1 GENERAL
2.1.1 Nominal -48v DC
Nominal –48v DC is the standard platform for power delivery to any Network Element (NE).
Manufacturers should comply with this requirement by providing their equipment internally with
various inverters and converters to meet this condition. The design criterion of the DC power is
based on a normal operating voltage of approximately -50v to -56v DC, with nominal rating of -
48v DC and low voltages of -42.6v DC measured at the termination point of the network
element.
2.1.1.1 AC Powered Equipment
AC powered equipment will only be considered for approval in the AT&T Telco network when
the inverter is embedded as part of the total equipment package.
2.1.2 Redundant Power Feeds
Redundant power feeders are required for all equipment serving network elements. The term
network element refers to all switching, transport, data, operator services equipment, and any
adjuncts for those elements.
Each element/shelf/circuit pack, whichever is the smallest independent load device of the NE,
shall obtain power from at least two power feeds. Furthermore, the return path from the power
units shall have individual return cabling from the source.
The use of “OR-ing” diode technology to combine power feeders may be used to power a
network element from two power sources provided all the following requirements are met:
a) Appropriately sized over-current protection devices shall be present in each power
path to the unit, within the network element.
b) Diodes shall also be included in each power path return of the unit.
c) The maximum steady state current to be handled by the diode shall be limited to 50%
of the diode’s maximum steady state current rating.
d) Current transients shall not exceed the maximum rated value for the diode.
e) The maximum reverse voltage across the diode shall be limited to 70% of the diode’s
peak inverse voltage rating
NE shall be designed to accept diverse power cable routing with inputs on each side of the NE.
2.1 Power Feeds
Redundant power feeder information must be provided in the supplier's response
documentation to be in compliance with this item. Power feeds (supply and return ) provided by
manufacturer’s shop wired configurations shall be paired and closely coupled.