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).

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. Remove the clear plastic cover protecting the terminal studs on the faceplate.
3. 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.

4. Remove the screws and square washers from the terminals. Use a number-2 Phillips screwdriver.
5. Secure each power cable lug to the terminals, first with the square washer, then with the screw. Apply between 23 lb-in. (2.6 Nm) and 25 lb-in. (2.8 Nm) of torque to each screw.
   • Secure each positive (+) DC source power cable lug to a RTN (return) terminal.
   • Secure each negative (–) DC source power cable lug to a –48V (input) terminal.
6. Replace the clear plastic cover over the terminal studs on the faceplate.
7. 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.
8. If you are installing multiple power supplies, repeat steps Step 1 through Step 7 for the other power supplies.

Figure 4: Connecting to DC Power, SRX 3400

Figure 5: Connecting to DC Power, SRX 3600