Calculating Power Requirements for the SRX5400 Firewall

The information in this topic helps you determine which power supply configurations are suitable for various firewall configurations, as well as which configurations are not suitable because output power is exceeded. You determine suitability by subtracting the total power draw from the maximum output of the power supplies. Afterward, the required input current is calculated. Finally, you calculate the thermal output.

We recommend that you provision power according to the maximum input current listed in the power supply electrical specifications (see SRX5400 Firewall AC Power Supply Specifications and SRX5400 Firewall DC Power Supply Specifications).

Use the following procedures to calculate the power requirement:

1. Calculate the power requirement.

2. Evaluate the power budget.

3. Calculate input power.

4. Calculate thermal output (BTUs) for cooling requirements.

The following sample configuration shows an SRX5400 Firewall chassis with various power supplies and:

• Two SRX5K-SPC-4-15-320 (SPC2) Services Processing Card (SPC) (slots 1 and 2)

• One SRX5K-MPC (IOC2) with two MICs installed in it (slot 1/0)

• One switch control board SRX5K-SCB (SCB1) or SRX5K-SCBE (SCB2) and one Routing Engine SRX5K-RE-13-20 (RE1) or SRX5K­RE-1800X4 (RE2) installed in it (SCB slot 0)

1. Calculate the power requirements (usage) as shown in Table 1.

   Table 1: Sample Power Requirements for an SRX5400 Firewall

   Chassis Component	Part Number	Power Requirement
   Base system	SRX5400-CHAS	40 W
   Fan tray	SRX5400-FAN	75 W
   MPC - slot 1/0	IOC2 SRX-MIC-2X40-QSFP SRX-QSFP-40G-SR4	570 W
   SPC - slots 1 and 2	SCP2	585 W * 2 = 1170 W
   SCB 0	SCB1 with RE1 Or	150 W 90 W
   	SCB2 with RE2	>150 W 90 W
   Total power requirement		2095 W
   Total power requirement excluding cooling system		2020 W

2. Evaluate the power budget. In this step, we check the required power against the maximum output power of available power supply options.

   Note:

   The power for the cooling system comes from a different tap on the power supply, reserved for the cooling system only. The cooling system power requirement does not need to be deducted from the output power budget of the power supply.

   Table 2 lists the power supplies, their maximum output power, and unused power (or a power deficit) for an AC-powered firewall. Table 3 lists the power supplies, their maximum output power, and unused power (or a power deficit) for a DC-powered firewall.

   Table 2: Calculating Power Budget, AC-Powered Chassis

   Maximum Output Power of Power Supply	Maximum Output Power for System	Unused Power
   1167 W (low-line)	1167W x 2 = 2334 W (2+1 Redundancy)	2334 - 2095 = 239W
   2050 W (high-line)	2050 x 2 = 4100 W (2+1 Redundancy)	4100 - 2095 = 2005W

   Table 3: Calculating Power Budget, DC Powered Chassis

   Maximum Output Power of Power Supply	Maximum Output Power for System	Unused Power
   2400 W (DIP=0)	2400 W (1+1 Redundancy)	2400 - 2095 = 305 W
   2600 W (DIP=1)	2600W (1+1 Redundancy)	2600 - 2095 = 505 W

3. Calculate input power. In this step, the input power requirements for the example configuration are calculated. To do this, divide the total output requirement by the efficiency of the power supply as shown in Table 4 Here we include the power drawn by the cooling system.

   Table 4: Calculating System Input Power

   Power Supply	Power Supply Efficiency1	Input Power Requirement
   SRX5400 AC	89 %	2095/0.89 = 2354 W
   SRX5400 DC	~98 %	2095/0.98 = 2138 W

   ¹ These values are at full load and nominal voltage.

4. Calculate thermal output (BTUs) for the system. To calculate this value, multiply the total input power requirement (in watts) by 3.41 as shown in Table 5.

   Table 5: Calculating System Thermal Output

   Power Supply	Thermal Output (BTUs per hour)
   SRX5400 AC	2354 * 3.41 = 8027 BTU/hr
   SRX5400 DC	2138 * 3.41 = 7291 BTU/hr

The following sample configuration shows an SRX5400 Firewall chassis with various power supplies and:

• Two SRX5K-SPC-4-15-320 (SPC2) Services Processing Card (SPC) (slots 1 and 2)

• One IOC3 (SRX5K-MPC3-40G10G or SRX5K-MPC3-100G10G) (slot 1/0)

• One switch control board SRX5K-SCB3 (SCB3) and one Routing Engine RE2 installed in SCB slot 0

1. Calculate the power requirements (usage) as shown in Table 6.

   Table 6: Sample Power Requirements for an SRX5400 Firewall with SCB3, IOC3, and RE2

   Chassis Component	Part Number	Power Requirement
   Base system	SRX5400-CHAS	40 W
   Fan tray	SRX5400-FAN	75 W
   MPC - slot 1/0	IOC3	607 W
   SPC - slots 1 and 2	SCP2	585 W * 2 = 1170 W
   SCB 0	SCB3 RE2	300 W 90 W
   Total power requirement		2282 W
   Total power requirement excluding cooling system		2207 W

2. Evaluate the power budget. In this step, we check the required power against the maximum output power of available power supply options.

   Note:

   The power for the cooling system comes from a different tap on the power supply, reserved for the cooling system only. The cooling system power requirement does not need to be deducted from the output power budget of the power supply.

   Table 7 lists the power supplies, their maximum output power, and unused power (or a power deficit) for an AC-powered firewall. Table 8 lists the power supplies, their maximum output power, and unused power (or a power deficit) for an AC-powered firewall.

   Table 7: Calculating Power Budget, AC-Powered Chassis

   Maximum Output Power of Power Supply	Maximum Output Power for System	Unused Power
   1167 W (low-line)	1167 x 2 = 2334 W (2+1 Redundancy)	2334 - 2282 = 52W
   2050 W (high-line)	2050 x 2 = 4100 W (2+1 Redundancy)	4100 - 2282 = 1818 W

   Table 8: Calculating Power Budget, DC Powered Chassis

   Maximum Output Power of Power Supply	Maximum Output Power for System	Unused Power
   2400 W (DIP=0)	2400W (1+1 Redundancy)	2400 - 2282 = 118W
   2600 W (DIP=1)	2600W (1+1 Redundancy)	2600 - 2282 = 318 W

3. Calculate input power. In this step, the input power requirements for the example configuration are calculated. To do this, divide the total output requirement by the efficiency of the power supply as shown in Table 9 Here we include the power drawn by the cooling system.

   Table 9: Calculating System Input Power

   Power Supply	Power Supply Efficiency1	Input Power Requirement
   SRX5400 AC	89 %	2282/0.89 = 2564 W
   SRX5400 DC	~98 %	2282/0.98 = 2329 W

   ¹ These values are at full load and nominal voltage.

4. Calculate thermal output (BTUs) for the system. To calculate this value, multiply the total input power requirement (in watts) by 3.41 as shown in Table 10.

   Table 10: Calculating System Thermal Output

   Power Supply	Thermal Output (BTUs per hour)
   SRX5400 AC	2564 * 3.41 = 8743 BTU/hr
   SRX5400 DC	2329 * 3.41 = 7941 BTU/hr