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Connect Power to a DC-Powered QFX5120 Switch

 

We ship the QFX5120 switches with two power supplies preinstalled. Each power supply is a hot-removable and hot-insertable field-replaceable unit (FRU) when the second power supply is installed and running: You can install power supplies in the slots next to the fan modules without powering off the switch or disrupting switch functions.

Note

The battery returns of the DC power supply must be connected as an isolated DC return (DC-I).

Before you connect DC power to the switch:

  • Ensure that you have taken the necessary precautions to prevent electrostatic discharge (ESD) damage (see Prevention of Electrostatic Discharge Damage).

  • Ensure that you have connected the switch chassis to earth ground (see Connect the QFX5120 Switch to Earth Ground).

    Caution

    Before you connect power to the switch, a licensed electrician must attach a cable lug to the grounding and power cables that you supply. A cable with an incorrectly attached lug can damage the switch (for example, by causing a short circuit).

    To meet safety and electromagnetic interference (EMI) requirements and to ensure proper operation, you must connect the chassis to earth ground before you connect it to power. For installations that require a separate grounding conductor to the chassis, use the protective earthing terminal on the switch chassis to connect to the earth ground.

Ensure that you have the following parts and tools available:

  • For the DC-powered models QFX5120-32C-DC-AFO and QFX5120-32C-DC-AFI: DC power cable with a plug—provided

  • For the DC-powered models QFX5120-48T-DC-AFO, QFX5120-48T-DC-AFI, QFX5120-48Y-DC-AFO2, and QFX5120-48Y-DC-AFI2: DC power source cables (14–16 AWG) with ring lug (Molex 190700069 or equivalent)—not provided

  • For the DC-powered models QFX5120-48YM-DC-AO and QFX5120-48YM-DC-AI: DC power source cables (14–12 AWG) with ring lug (Molex 190700069 or equivalent)—not provided

  • Number 2 Phillips (+) screwdriver—not provided

  • Multimeter—not provided

To connect power to a DC-powered QFX5120-32C switch:

  1. Wrap and fasten one end of the ESD wrist strap around your bare wrist, and connect the other end of the strap to a site ESD point.
  2. Ensure that the input circuit breaker is open so that the voltage across the DC power source cable leads is 0 V and that the cable leads do not become active while you are connecting DC power.
  3. Ensure that the power supplies are fully inserted in the chassis.
  4. Connect each power supply to the power source by inserting the DC connector of the power cable provided into the power supply (see Figure 1).
    Figure 1: Connect Power to a DC-Powered QFX5120-32C Switch
    Connect Power to a DC-Powered QFX5120-32C Switch
  5. Connect each power cable to the power sources. Secure power source cables to the power supplies by screwing the ring lugs attached to the cables to the appropriate terminals.

    • Connect the ring lug of the green-yellow cable to earth ground.

    • Connect the ring lug of the black cable to the negative (–) DC power source.

    • Connect the ring lug of the red cable to the positive (+) DC power source.

    We’ve designed the QFX5120-32C switch to operate with a DC power supply that has a single, nonredundant feed input. For source redundancy, you must install two DC power supplies in the QFX5120-32C; connect source (A) to one power supply and connect source (B) to the second power supply. This configuration provides the commonly deployed A/B feed redundancy for the system.

    Caution

    The connection between each power source and power supply must include a circuit breaker. Do not connect two sources to a single power supply because doing so can potentially cause circulating current in feed wires whenever there is any difference in the voltage of the two sources.

  6. Close the input circuit breaker.Note

    The QFX5120 switch powers on as soon as power is provided to the power supply. There is no power switch on the QFX5120.

  7. Verify that the LED on the power supply is lit green. If the LED is lit or blinking red, disconnect the power supply from the power source, and replace the power supply (see Remove a Power Supply from a QFX5120 Switch).Caution

    Do not remove the power supply until you have a replacement power supply ready: you must install the replacement power supply within one minute after removing the failed power supply to ensure proper airflow and prevent chassis overheating.

To connect power to a DC-powered QFX5120-48T, QFX5120-48Y, or QFX5120-48YM switch:

  1. Wrap and fasten one end of the ESD wrist strap around your bare wrist, and connect the other end of the strap to a site ESD point.

  2. 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 low resistance (indicating a closed circuit) to chassis ground is positive (+) and will be installed on the V+ (return) DC power input terminal.

    • The cable with very high resistance (indicating an open circuit) to chassis ground is negative (–) and will be installed on the V– (input) DC power input terminal.

    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 coding for DC power cables. The coding used by the external DC power source at your site determines the coding for the leads on the power cables that attach to the DC power input terminals on each power supply.

  3. Ensure that the input circuit breaker is open so that the voltage across the DC power source cable leads is 0 V and that the cable leads do not become active while you are connecting DC power.Note

    The V+ terminals are referred to as +RTN, and the V– terminals are referred to as –48 V in DC Power Wiring Sequence Warning and DC Power Electrical Safety Guidelines.

  4. Ensure that the power supplies are fully inserted in the chassis.
  5. Remove the terminal block cover. The terminal block cover is a piece of clear plastic that snaps into place over the terminal block.
  6. Remove the screws on the terminals using the screwdriver. Save the screws.Warning

    Ensure that the power cables do not block access to device components or drape where people can trip on them.

  7. Connect each power supply to the power sources. Secure power source cables to the power supplies by screwing the ring lugs attached to the cables to the appropriate terminals by using the screw from the terminals (see Figure 2).

    We’ve designed the QFX5120-48T, QFX5120-48Y, and QFX5120-48YM switches to operate with a DC power supply that has a single, nonredundant, feed input. For source redundancy, you must install two DC power supplies in the QFX5120-48T, QFX5120-48Y, and QFX5120-48YM switches; and then connect source (A) to one power supply and connect source (B) to the second power supply. This configuration provides the commonly deployed A/B feed redundancy for the system.

    The terminal block of the power supply has four terminals labeled V+, V+, V–, and V– for connecting DC power source cables labeled positive (+) and negative (–). The V+ terminals are shunted internally together, as are the V– terminals.

    Caution

    The connection between each power source and power supply must include a circuit breaker.

    Do not connect two sources to a single power supply because doing so can potentially cause circulating current in feed wires whenever there is any difference in the voltage of the two sources.

    1. Secure the ring lug of the positive (+) DC power source cable to the V+ terminal on the DC power supply.
    2. Secure the ring lug of the negative (–) DC power source cable to the V– terminal on the DC power supply.
    3. Tighten the screws on the power supply terminals until snug using the screwdriver. Do not overtighten; apply between 5 lb-in. (0.56 Nm) and 6 lb-in. (0.68 Nm) of torque on the screws.
    Caution

    The V+ terminals are shunted internally together, as are the V- terminals. The same polarity terminal can be wired together from the same source to provide an additional current path in a higher power chassis. Do not connect the terminals to different sources.

    Figure 2: Secure Ring Lugs to the Terminals on the QFX5120-48T, QFX5120-48Y, or QFX5120-48YM DC Power Supply
    Secure Ring Lugs to the Terminals on the QFX5120-48T, QFX5120-48Y, or QFX5120-48YM DC Power Supply
  8. Replace the terminal block cover.
  9. Close the input circuit breaker.Note

    The QFX5120 switch powers on as soon as power is provided to the power supply. There is no power switch on the QFX5120.

  10. Verify that the IN and OUT LEDs on the power supply are lit green. If the fault LED (!) is lit, disconnect the power supply from the power source, and replace the power supply (see Remove a Power Supply from a QFX5120 Switch).Caution

    Do not remove the power supply until you have a replacement power supply ready: you must install the replacement power supply within one minute after removing the failed power supply to ensure proper airflow and prevent chassis overheating.