The answer depends on the type of modules used within the chassis. For chassis with passive modules, the DC power connection is for the TL (Tracer Lamps) or LEDs. These TLs or LEDs are activated when a connector is inserted into a monitor port and have no impact on the data being transmitted. Telect recommends connecting power to take advantage of the TL/LED functionality, but power has no impact on the transmission of data through a passive module. 

When using our "Active Modules" within the DSX-3 BCS and DSX-3 BCS II chassis, power is required. Loss of power would be service affecting. 

The BCS chassis include:  010-0000-1401, 010-0000-1471, 010-0000-1448, 010-0000-0401, 010-0000-0471
The BCS II chassis include: 010-0000-1401 BCS, 010-0000-2401 BCS, 010-0000-3201 BCS, 010-0000-0471 BCS, 010-0000-1471 BCS

These BCS modules are active:
Repeater Modules: 710-8401-0002, 710-8401-0005

These BCS II modules are active:
Repeater Modules: 710-3201-0002, 710-3201-0005
Ethernet extensions: 710-3201-1301-E, 710-3201-1302-E, 710-3201-2301-E, 710-3201-2302-E
T3/E3/STS-1 Extensions: 710-3201-1001-U, 710-3201-1002-U, 710-3201-2001-U, 710-3201-2002-U
Single-Fiber T3 Extension Modules: 710-3201-4222-U
 
Certain chassis have dual power inputs (A and B sides) for redundancy. The TL LEDs pull power only from the A side. When active modules are used, Telect highly recommends connecting both the "A" and "B" side power inputs to take advantage of redundant power sources.