3. Calculate the maximum system power consumption by dividing the maximum internalpower consumption by the efficiency of the power supply. This accounts for the lossof energy within the power supply.NOTE: The efficiency of a 2000 W AC power supply is approximately 90percent when input voltage is high line (200–240 VAC).The efficiency of a 2000 W AC power supply is approximately 87 percentwhen 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 powerredundancy with high-line input voltage, the maximum system power consumption:= (maximum internal power consumption) / (power supply efficiency)= (5200 W) / (0.90)= 5778 WCalculating System Thermal Output for Your J-EX8208 Switch ConfigurationUse the following procedure to calculate the system thermal output in British thermalunits (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 J-EX8208 Switch Configuration” onpage 79 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 powerredundancy with high-line input voltage, the system thermal output:= (maximum system power consumption) x (3.41)= (5778 W) x (3.41) == 19,703 BTU/hrNOTE: Using the maximum system power consumption values to calculatethe system thermal output often results in overprovisioning the coolingsystems. Typical power consumption is about one-third lower than thesecalculated values.Calculating the Number of Power Supplies Required for Your J-EX8208 Switch ConfigurationUse this procedure to calculate the number of power supplies required by your switchconfiguration. The required power configuration for J-EX8208 switches is N+1. You canoptionally configure your switch for N+N configuration. For example, you might wantdual power feed redundancy with AC power supplies, which requires an N+N configuration.81Chapter 7: Planning Power Requirements
