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December 20, 2004 Chapter 1: Product Description
LTPH-UM-1261-01 1-5
POWER AND ALARM CONNECTIONS
The HMS-318 List 3 shelf has a separate split input power (TB1) and an Alarms wire-wrap field (TB2). The following
paragraphs provide information about TB1 and TB2.
Safety Precautions
Observe the following general precautions and recommendations in planning the source power requirements for the
HMS-318 List 3 shelf (for additional safety information, please refer to the section describing the “Safety Guidelines”
on page xi):
• Check the power at your site before shelf installation (and periodically after installation) to ensure clean power is
being received.
• Always disconnect the power source and unplug all the power cables before working on the shelf.
• Install proper grounding for the site to avoid damage from lightning and power surges.
Input Power Terminal Block
The 5-position input power terminal block (TB1, see Figure 1-3) provides a central connection point for the CO
primary power feeds (A and B).
Figure 1-3. Input Power Terminal Block (TB1)
HMS-318 List 3 Shelf Input Power Connections
The input power terminal block supports split -48V battery power bussing. Slots 1 through 11 on the HMS-318 List 3
shelf are powered by the -48 Vdc A bus (labeled -48VA). Slots 12 through 22 are powered by the -48 Vdc B bus
(labeled -48VB). The two GND terminals are tied together. In the HMU/HLU configuration, the HMU-319 is diode-
OR’ed to both power busses, to guard against power failure in the event that one power supply is lost. This feature
requires the two ground terminals to be tied together on the HMU card (for proper power and grounding of the HLU-
319 and HMU-319, see “Related Publications” on page 1-ix and choose the most appropriate instruction manual for
your product).
DANGER
To avoid electrical shock, be careful when working near power supplies. Telco equipment uses -
48 Vdc office power.
CAUTION
Before making any power connections (CO primary power feeds A and B) to the HMS-318 List 3
shelf, ensure that the Main CO power breaker is off. Otherwise, severe injury to the installer or
damage to the unit may result.
-48VA
FUSE
1234
5
-48VB
FUSE
BAT RTN
FGND
TB1
15A MAX 15A MAX
USE
SUPPLIED BRIDGE