Juniper MX2008 Hardware Manual page 218

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The information in this topic helps you determine which of the two input ratings for the PSM is suitable
for various configurations. You determine suitability by subtracting the total power draw from the maximum
output of the PSMs. Afterward, you calculate the required input current. Finally, you calculate the thermal
output.
We recommend that you provision power according to the maximum input current listed in the power
system electrical 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.
To calculate the AC power requirements:
1. Calculate the power (usage) using the values (see "MX2008 AC Power Requirements" on page 74).
2. Evaluate the power budget, including the budget for each configuration if applicable, and check the
required power against the maximum output power of available PDM options.