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The STB NIP 2212 NIM
890USE17700 April 2004 39
Selecting a Source Power Supply for the Island’s Logic Power Bus
Logic Power
Requirements
An external 24 VDC power supply is needed as the source for logic power to the
island bus. The external power supply connects to the island’s NIM. This external
supply provides the 24 V input to the built-in 5 V power supply in the NIM.
The NIM delivers the logic power signal to the primary segment only. Special
STB XBE 1200 beginning-of-segment (BOS) modules, located in the first slot of
each extension segment, have their own built-in power supplies, which will provide
logic power to the STB I/O modules in the extension segments. Each BOS module
that you install requires 24 VDC from an external power supply.
Characteristics
of the External
Power Supply
The external power supply needs to deliver 24 VDC source power to the island. The
supply that you select can have a low range limit of 19.2 VDC and a high range limit
of 30 VDC. The external supply must be rated safety extra low voltage (SELV-rated).
The SELV-rating means that SELV isolation is provided between the power supply’s
inputs and outputs, the power bus, and the devices connected to the island bus.
Under normal or single-fault conditions the voltage between any two accessible
parts, or between an accessible part and the protective earth (PE) terminal for Class
1 equipment, will not exceed a safe value (60 VDC max.).
CAUTION
IMPROPER GALVANIC ISOLATION
The power components are not galvanically isolated. They are intended
for use only in systems designed to provide SELV isolation between the
supply inputs or outputs and the load devices or system power bus. You
must use SELV-rated supplies to provide 24 VDC source power to the
NIM.
Failure to follow this precaution can result in injury or equipment
damage.