Power Definitions

Power Definitions

What is an Amp?

An Amp (or Ampere) is the standard measure of electrical current.  Much like water flowing through a pipe, the Amp is a measure of how much electricity is moving through a wire at a given time.  The Amp draw of a circuit is dependent on the needs of the devices plugged into it, and is limited by the branch circuit protection.

What is a Volt?

A Volt is the standard measure of electrical potential and a fixed value for every circuit. Voltage is measured with respect to a reference point (usually between the two respective conductors of the circuit). Voltage is analogous to pressure in a water pipe. Higher pressures, or higher voltages, allow more energy to flow within a given amount of time for a given wire size. Standard voltages present in most data centers are 120V and 208V in the U.S., and 230V in continental Europe. Some newer U.S. data centers are being designed to utilize 230V.

What is a Watt?

A Watt is the measure of total work performed by the energy consumed in a system. The calculation is: Watts = Volts x Amps x Power Factor.

What is Energy?

Energy is electricty as a raw material, measured in Volts and Amps available to do work.

What is AC?

Alternating Curent, or AC, is energy delivered in a form that can travel the long distances necessary from generating plants to homes and businesses. The term AC reflects the fact that the voltage and current are always changing in value, or alternating between a positive and negative threshold over a centerline.

What is DC?

Direct Current, or DC, is energy that does not alternate over a fixed period of time, but rather has a steady value with reference to zero. DC does not travel great distances well.

What does RMS mean?

RMS stands for Root-Mean-Squared. It is used in conjunction with AC Volts and AC Amps to express an average value. A true RMS calculation takes into account the shape and phases of the wave forms being delivered to a circuit. AC voltage and current are ever-changing values. Using RMS measurements provides useful values.

What is Apparent Power?

Apparent Power is the instantaneous calculation of Volts x Amps.

What is Real Power?

Real Power is the RMS value of Watts.

What is PUE?

PUE stands for Power Use Effectiveness. PUE is a measure of how efficiently power is being used in a data center, and is becoming the standard benchmarking metric in most data centers. PUE is determined by dividing the total facility power use (Building Watts) by the IT equipment load (IT Watts). The power distribution within the building has several points where losses occur (UPS, transformers, wire runs), so the ideal place to measure the IT power load is at the cabinet level within the power strip. These readings can be collected and aggregated to determine the IT power load. Once an initial assessment of PUE has been made, efforts can be made to improve PUE by applying various methods to improve operational efficiencies in the data center.

What is DCiE?

DCIE stands for Data Center Infrastructure Efficiency. DCIE is IT Power divided by Total Facility Power, expressed as a percent (%). DCIE is the inverse of PUE.