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• AC Power Supply in an EX8200 Switch
• DC Power Supply in an EX8200 Switch
• Understanding Power Management on EX Series Switches

Calculating Power Requirements for an EX8208 Switch

Use the information in this topic to calculate power consumption, system thermal output, and number of power supplies required for different EX8208 switch configurations.

Before you begin these calculations:

• Ensure you understand the different switch configurations. See EX8208 Switch Configurations.
• Ensure that you know the power requirements of different switch components. See Power Requirements for EX8208 Switch Components.

This topic describes these tasks:

• Calculating the Power Consumption of Your EX8208 Switch Configuration
• Calculating System Thermal Output for Your EX8208 Switch Configuration
• Calculating the Number of Power Supplies Required for Your EX8208 Switch Configuration

Calculating the Power Consumption of Your EX8208 Switch Configuration

Use the following procedure to determine the maximum power you need to supply to the switch. To calculate maximum system power consumption, you first determine the combined maximum internal power requirements of all the switch components and then divide this result by the power supply efficiency.

To calculate maximum system power consumption:

1. Determine the maximum power consumption of the base chassis components (that is, the components other than the line cards):
   • Use Table 1 if your switch is configured for N+1 power redundancy or if your switch is configured for N+N power redundancy and is running JUNOS Release 10.1 or earlier.
   • Use Table 2 only if your switch is running JUNOS Release 10.2 or later and power management is configured for N+N power redundancy.

   Note: In JUNOS Release 10.2 or later, if power management is configured for N+N redundancy, the maximum fan speed is lowered, reducing the chassis’ maximum power consumption.

   Table 1: Chassis Power Consumption for N+1 Configurations and for N+N Configurations Running JUNOS Release 10.1 or Earlier

   Chassis Component	Base Configuration	Redundant Configuration
   Fan tray	1100 W	1100 W
   Switch Fabric and Routing Engine (SRE) module	200 W	200 W
   Second SRE module	—	200 W
   Switch Fabric module	100 W	100 W
   Total	1400 W	1600 W

   Table 2: Chassis Power Consumption for N+N Configurations Running JUNOS Release 10.2 or Later

   Chassis Component	Base Configuration	Redundant Configuration
   Fan tray	700 W	700 W
   SRE module	200 W	200 W
   SRE module	—	200 W
   SF module	100 W	100 W
   Total	1000 W	1200 W

2. Calculate the maximum internal power consumption of the entire switch by adding in the power requirements of each line card.

   For example, for a switch fully loaded with 8-port SFP+ line cards and using N+1 power redundancy, the maximum internal power consumption:

   = (chassis watts) + 8 (8-port SFP+ line card watts)

   = (1600 W + 8 (450 W))

   = (1600 W + 3600 W)

   = 5200 W

3. Calculate the maximum system power consumption by dividing the maximum internal power consumption by the efficiency of the power supply. This accounts for the loss of energy within the power supply.

   Note: The efficiency of a 2000 W AC power supply is approximately 90 percent when input voltage is high line (200–240 VAC). The efficiency of a 2000 W AC power supply is approximately 87 percent when input voltage is low line (100–120 VAC).

   For example, for a switch fully loaded with 8-port SFP+ line cards and using N+1 power redundancy with high-line input voltage, the maximum system power consumption:

   = (maximum internal power consumption) / (power supply efficiency)

   = (5200 W) / (0.90)

   = 5778 W

Calculating System Thermal Output for Your EX8208 Switch Configuration

Use the following procedure to calculate the system thermal output in British thermal units (BTU) per hour for your switch configuration.

To calculate the system thermal output:

1. Determine the maximum system power consumption of your switch in watts. See Calculating the Power Consumption of Your EX8208 Switch Configuration for how to do so.
2. Multiply the maximum system power consumption by 3.41.

   For example, for a switch fully loaded with 8-port SFP+ line cards and using N+1 power redundancy with high-line input voltage, the system thermal output:

   = (maximum system power consumption) x (3.41)

   = (5778 W) x (3.41) =

   = 19,703 BTU/hr

Note: Using the maximum system power consumption values to calculate the system thermal output often results in overprovisioning the cooling systems. Typical power consumption is about one-third lower than these calculated values.

Calculating the Number of Power Supplies Required for Your EX8208 Switch Configuration

Use this procedure to calculate the number of power supplies required by your switch configuration. The required power configuration for EX8208 switches is N+1. You can optionally configure your switch for N+N configuration. For example, you might want dual power feed redundancy with AC power supplies, which requires an N+N configuration.

To calculate the number of power supplies required for your switch configuration:

1. Determine the power requirement of the base chassis (that is, the combined power requirements of the fan tray, SRE module or modules, and the SF module) by consulting Table 3.

   The watt values shown in Table 3 are the amount of power reserved by power management for the chassis in its power budget. It uses these values when calculating used and available power and when determining whether sufficient power exists to meet N, N+1, or N+N requirements.

   Starting with JUNOS Release 10.2, when power management is configured for N+N power redundancy, it reserves less power for the chassis so that more power is available for line cards.

   Table 3: Power Reserved for the Chassis

   	JUNOS Release 10.1 or Earlier	JUNOS Release 10.2 or Later
   N+1 Configuration	1600 W	1600 W
   N+N Configuration	1600 W	1200 W

   Note: The amount of power that power management reserves for the chassis is a set value that does not vary depending on chassis components installed. The reserved power is the same for base and redundant configurations and for switches that do not have all base chassis components installed.

2. To the power reserved for the chassis, add the power requirements of the line cards.

   For line card power requirements, refer to Power Requirements for EX8208 Switch Components.

   For example, for a switch fully loaded with 8-port SFP+ line cards and using N+1 power redundancy, the total power requirement:

   = reserved chassis power + 8 (8–port SFP + line cards)

   = 1600 W + 8 (450) W

   = 1600 W + 3600 W

   = 5200 W

   For a switch fully loaded with 8-port SFP+ line cards, using N+N power redundancy, and running JUNOS Release 10.2, the total power requirement:

   = reserved chassis power + 8 (8–port SFP + line cards)

   = 1200 W + 8 (450) W

   = 1200 W + 3600 W

   = 4800 W

3. Calculate the number of power supplies (N) required to meet the total power requirement by dividing the total power requirement by the output wattage of one power supply and then rounding up.

   Note: If the input voltage is high line (200–220 VAC), the output wattage of a 2000 W AC power supply is 2000 W. If the input voltage is low line (100–120 VAC), the output wattage of a 2000 W AC power supply is 1200 W.

   For example, for a switch fully loaded with 8-port SFP+ line cards and using N+1 power redundancy with high-line input voltage, the required power supplies (N):

   = (total power requirement) / (output wattage of power supply)

   = (5200 W) / (2000 W)

   = 2.6

   = 3 (rounded up)

   For a switch fully loaded with 8-port SFP+ line cards, using N+N power redundancy with high-line input voltage, and running JUNOS Release 10.2, the required power supplies (N):

   = (total power requirement) / (output wattage of power supply)

   = (4800 W) / (2000 W)

   = 2.4

   = 3 (rounded up)

4. Add the number of power supplies needed to achieve the required power redundancy:
   • To achieve N+1 power redundancy, add a single power supply.

     For example, for a switch fully loaded with 8-port SFP+ line cards and using high-line input voltage, the total number of power supplies:

     = N + 1

     = 3 + 1

     = 4

   • To achieve N+N power redundancy, add N power supplies.

     For example, for a switch fully loaded with 8-port SFP+ line cards and using high-line input voltage, the total number of power supplies:

     = N + N

     = 3 + 3

     = 6

Note: We recommend that you maintain N +1 or N+N power supplies in your switch at all times. Replace failed power supplies immediately to prevent unexpected failures. Power management raises a minor alarm if the number of online power supplies in your switch is less than the number required to maintain the configured power redundancy (N+1 in JUNOS Release 10.1 or earlier; N+1 or N+N in JUNOS Release 10.2 or later). If the problem is not corrected in 5 minutes, a major alarm is issued. Power management raises a major alarm if the number of online power supplies in your switch is less than N power supplies. If your switch is running JUNOS Release 10.1 or earlier, all line cards are powered off. If your switch is running JUNOS Release 10.2 or later, power management provides power to line cards in priority order until power is exhausted. The remaining line cards are powered off. If a new line card is installed in an operational switch, power management does not power on the line card if the increased power demand exceeds the total available power, including redundant power. If redundant power is used to power on the line card, a minor alarm is raised, which becomes a major alarm in 5 minutes if the condition is not corrected.