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Connecting the SRX550 Services Gateway to a DC Power Source


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

A 645 W DC power supply with PoE support is available for the SRX550 Services Gateway.


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 (O), 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 terminals on the power supply faceplate. You must provide the power cables.

The power supply has two sets of terminals, to accommodate a redundant DC power feed. If one feed fails, the services gateway draws its power from the other feed. The terminals for Feed A are labeled A+ and A- . The terminals for Feed B are labeled B+ and B-. You do not need to use both feeds; if you only have one DC power source, or if you do not want to use feed redundancy, you can connect just one feed.

To connect the DC source power cables to the services gateway 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. Attach an electrostatic discharge (ESD) grounding strap to your bare wrist, and connect the strap to the ESD point on the back panel of the chassis.
  3. Remove the clear plastic cover protecting the terminals on the power supply 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 the resistance 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.

    • The cable with very low resistance (indicating a closed circuit) to chassis ground will be RTN.


    The DC cable should be of minimum 14 AWG.


    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 terminals on the power supply.

  5. Connect DC power cables to the A+ and A- terminals:
    1. Remove the screws and square washers from the A+ and A- terminals. Use a Phillips (+) screwdriver, number 2. The square washers are permanently attached to the screws.
    2. Secure each power cable lug to the appropriate terminal with a screw. Apply between 23 lb-in. (2.6 Nm) and 25 lb-in. (2.8 Nm) of torque to each screw.
      • Secure the positive (+) DC source power cable lug to the A+ (return) terminal.

      • Secure the negative (–) DC source power cable lug to the A- (input) terminal.

    Figure 1: Connecting DC Power Cables
    Connecting DC Power Cables
  6. (Optional) If you have two DC power sources and wish to deploy A/B feed redundancy for the services gateway, connect the DC power cables to B+ and B- terminals also.
  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.

The services gateway must be connected to earth ground during normal operation. The protective earthing terminal on the back panel of the chassis is provided to connect the services gateway to ground.