Common Systems Connection Standards AT&T Services, Inc
Date: August 31, 2007 ATT-TP-76450, Issue 9
Copyright ©2004 – 2006, AT&T Knowledge Ventures
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Page 10
Circuit Breakers - Only thermal magnetic and magnetic type DC circuit breakers are
acceptable. Circuit breakers should adhere to all applicable UL and ANSI standards. DC Circuit
breakers that are labeled 100% are full load rated and may be sized at the same capacity as
the List 2X drain.
• NOTE: Due to the circuit protection strategy deployment found in AT&T companies,
the use of circuit breakers placed in the power architecture should be avoided when a
fuse provides the next step of protection (generally found at the BDFB). It is
recommended that circuit breakers be protected by circuit breakers, fuses with fuses
or fuses protected by circuit breakers. The use of circuit breakers placed in the
embedded power distribution units found in network elements should be avoided.
The preferred method of circuit protection at this level is fuses.
2.6.1 All fuses and circuit breakers shall meet Quality Level III as defined by Telcordia
SR-332.
2.6.2 Filtered Battery
All Network Elements requiring “Filtered Battery” shall provide the filtering within the Network
Element. (Filtered DC power PDUs are not provided by AT&T to remove excessive levels of
transient noise generated within the Network Element).
2.7 Individually Mounted PDU
Even though not recommended as a choice by AT&T, some Network Elements designed by
various manufacturers require specific PDUs that include unique characteristics needed to
serve their specific network device. These “special PDUs” must meet all the same design
criteria identified in this document as well as the ATT-TP-76200 NEBS publication. If accepted,
this “special PDU” would be listed as part of the Network Element approval, purely as an
integral part of the package and its approval is exclusive to the associated network element.
Furthermore, this “special PDU” should be reviewed by the Common Systems Technical Staff
to insure its integrity.
2.8 NE Integrated Power Distribution
Defined as; power distribution that is integrated within the framework of the network element
(e.g. #5 ESS PDF frame). Generally speaking, NEs requiring more that 200 amps of DC power
need this type of power distribution. The NEs are commonly found in large multiple interrelated-
bays.
These type devices are considered equipment specific and should meet the requirements as
listed in Section 1 of this document as well as the ATT-TP-76200 NEBS publication.
Additionally, AT&T recommends the use of fuses in lieu of breakers in these applications.
2.9 Direct BDFB Power Delivery
