John Fragalla
Dell's John Fragala

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Amps of a HPC System is derived from the equation Wattage divided by Voltage (A = W/V). The Wattage, or just Watts, is usually the highest power consumption measured when running Linpack, as discussed in Part 2 of this blog. The voltage depends on the customer’s data center, but typical voltage used in the United States (US) is 208V. Amps is a critical measurement needed for a HPC system because it helps size the appropriate rack Power Distributions Units (PDUs) that is compatible with a customer’s data center.

Rack PDUs come in different configurations, ranging from single phase power, to three phase power, and different amps per phase, such as 30A to 60A. Each HPC component, such as the compute nodes, switches, storage, has different circuit types, such as C13 or C19. When racking HPC components in a rack, one must find the appropriate rack PDUs to support the correct type of circuits to power up each of the HPC components. The decision between single phase or three phase power, and the amps per phase, is typically dictated by what is configured and support in each of the customer’s data center.

After deciding on the correct rack PDU with the correct circuit type and type of power supported in the data center, another aspect to consider on the rack PDUs are breakers protecting a branch of circuits. Typically, these breakers are 20A, and in some cases in the US, they are de-rated by 80% to 16A due to UL specification. On the rack PDUs, 16A to 20A is the maximum amount of amps that breaker can support before tripping the breaker. The HPC component amps can be plugged into each branch of circuits without exceed 16A or 20A, depending on the breaker capacity and if they are de-rated.

In some cases, depending on the amps per rack, one might need multiple rack PDUs per rack to balance the load across circuit breakers and phases to ensure, under peak load when running Linpack, no breakers are exceeding the maximum specification.

In Part 4 of this blog, the next important topic to discuss for a HPC system is Cubic Feet per Minute (CFM), which is a measurement of air flow a HPC system produces from component fans.

Read HPC Power and Cooling: Power Consumption - Part 1
Read HPC Power and Cooling: Power Consumption - Part 2

-- John Fragalla

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