Connecting Power to a DC-Powered Services Gateway

Caution: Do not mix AC and DC power supplies within the same device. Damage to the device might occur.

Warning: Before performing the following procedure, ensure that power is removed from the DC circuit. To ensure that all power is off, locate the circuit breaker on the panel board that services the DC circuit, switch the circuit breaker to the off position, and tape the switch handle of the circuit breaker in the off position.

You connect DC power to the device by attaching power cables from the external DC power sources to the terminal studs on the power supply faceplates. You must provide the power cables (the cable lugs are supplied with the device). For power cable specifications, see DC Power Cable Specifications.

To connect the DC source power cables to the device for each power supply:

1. Switch off the dedicated facility circuit breakers. Ensure that the voltage across the DC power source cable leads is 0 V and that there is no chance that the cable leads might become active during installation.
2. Switch the circuit breaker on the power supply faceplate to the OFF position.
3. Remove the clear plastic cover protecting the terminal studs on the faceplate.
4. Verify that the DC power cables are correctly labeled before making connections to the power supply. In a typical power distribution scheme where the return is connected to chassis ground at the battery plant, you can use a multimeter to verify that the ohm output of the –48V and RTN DC cables to chassis ground. . The cable with very large resistance (indicating an open circuit) to chassis ground will be –48V and the cable with very low resistance (indicating a closed circuit) to chassis ground will be RTN.

   Caution: You must ensure that power connections maintain the proper polarity. The power source cables might be labeled (+) and (–) to indicate their polarity. There is no standard color coding for DC power cables. The color coding used by the external DC power source at your site determines the color coding for the leads on the power cables that attach to the terminal studs on each power supply.

5. Remove the nuts and washers from the terminal studs. (Use a 3/8-in. nut driver or socket wrench.)
6. Secure each power cable lug to the terminal studs, first with the flat washer, then with the nut (see Figure 36). Apply between 23 lb-in. (2.6 Nm) and 25 lb-in. (2.8 Nm) of torque to each nut. .(Use a 3/8-in. nut driver or socket wrench.)
   • Attach the positive (+) DC source power cable lug to the RTN (return) terminal.
   • Attach the negative (–) DC source power cable lug to the –48V (input) terminal.

     Note: The DC power supplies in PEM0 and PEM1 must be powered by dedicated power feeds derived from feed A, and the DC power supplies in PEM2 and PEM3 must be powered by dedicated power feeds derived from feed B. This configuration provides the commonly deployed A/B feed redundancy for the system.

7. Replace the clear plastic cover over the terminal studs on the faceplate.
8. Verify that the power cables are connected correctly, that they are not touching or blocking access to services gateway components, and that they do not drape where people could trip on them.
9. If you are installing two power supplies, repeat Steps Step 2 through Step 8 for the other power supply.

Figure 36: Connecting DC Power to the Services Gateway