Rack Power – Power Distribution Units (PDU)

Today’s Data center are filled with power and storage devices with increase in power needs. We have to select the best rack Power Distribution Units (PDU) for that environment. In this blog, I will share some basic power terms and few details about rack PDU. 

• Ampere (Amp): It measures the amount of electrical current flowing through a circuit during a specific time period. It is also known as Amps. 
• Volt (V): It is equal to the difference of electric potential between two points on a conducting wire. 
• Volt-Amps (VA): It is the voltage multiplied by amps (Voltage * Amps). This rating is the apparent power, which represents the maximum power that a device can draw. Kilovolt-Amps (KVA) is the measure of VA in thousands. i.e. 2000 VA = 2KVA. 
• Watt (W): It is the measure of real power drawn by load equipment. It is used as the measurement of both power and heat generated by the equipment. 
• Power Factor: It is the ratio of real power to the apparent power. In other words, it can also be described as the power that is being being supplied Vs the power that is consumed. Most modern IT equipment has the power factor of 1, which means that the equipment efficiently uses the power supply and factors less than 1 signifies the less efficient equipment. 
• Circuit Breaker: It is a switch that protects electrical equipment from damage caused by overload or short circuit.

Data Center power is distributed with 208V single phase, high line power. Also it can be distributed with three phase power. Three phase power is used because of its efficiency and power delivering. The National Electrical Code (NEC) is the United States standard for safe insulation of electrical wire in an equipment. It states that, PDU cannot allow a continuous measure load that exceeds more than 80 % of the connector or cable rating. NEC defines the continuous load as 3 hours or longer. This is sometimes referred to as Derated Load, i.e. a 30 AMP rack PDU can only carry a maximum continuous load of 24 AMP. The NEC rated load on a rack PDU needs to be considered when data center operators want to provide power redundancy for their equipment. Without power redundancy, if the rack PDU fails the all equipment’s will shut down. To prevent this all important servers and infrastructure equipment should have multiple power supply and plugins to at least two different PDUs. Best practice is, never go above 50% of the PDU capacity. This is called PDU power balancing and provides power redundancy.  

In my next blog, I will share some details about how to select the rack PDU for your data center. Stay Tuned.......