HP DL360 Power basics for IT professionals - Page 42

UL: Underwriters Laboratories, an alternating waveform in the other winding. As such

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Shielded-type cable: A cable in which the conductors (wires) are enclosed in a conducting envelope constructed so that virtually every point on the surface of the insulation is at ground potential. Short circuit: An undesired electrical connection or crossover between two or more components (such as a live wire touching a ground, a neutral wire, or a device's metal casing). Single-phase power: The 120V electric current that is standard in U.S. homes. Spike: A brief instance of high voltage or current. Supply air: The incoming air flow of air conditioning provided to cool a data center. Surge: A sudden increase in voltage (volts) or current (amperes). Surge protector: A protected power outlet that, when placed between electronic equipment and the electric power supply, guards against a power surge by breaking the circuit. Temperature rating: The maximum temperature at which an insulating material may be used in continuous operation without loss of its basic properties, or the maximum temperature at which an electrical device may be used in continuous operation without failure of its capacity specifications. Terminal: Any device attached to the conductor (wire) by crimping, soldering or welding. Three-phase power: The 120V/240V electric current that is standard in U.S. office buildings and data centers. Three-wire single-phase power: Commonly used in North America for single-family residential and light commercial facilities. Three-wire single-phase power is sometimes incorrectly referred to as "twophase" power because it has two live conductors. A connection across two live wires delivers 240V for heavy or heating appliances with less current and smaller conductors than necessary at 120V. No individual conductor carries more than 120V over ground, so less insulation is required than for single-ended 240V power. Tolerance: The acceptable range of variance above or below the specified power rating or any other standard or specification of measurement. Transformer: An electrical device that transfers energy from one electrical circuit to another by different magnetic couplings (ferrite coils or windings) without moving parts. A transformer is used to convert between high and low voltages and between low and high currents. (If the voltage goes up, the current must go down, and vice versa.) An alternating waveform applied to one winding induces an alternating waveform in the other winding. As such, the transformer is an important element in the transition (typically at efficiencies of 95 percent) between high-voltage power transmission via central generating stations and low-voltage power used by homes and businesses. Two-phase power: Used in some factories in the early 1900s, two-phase power was usually supplied using four wires, two for each phase. (Less frequently, three wires were used, with a common wire with a larger-diameter conductor.) Because three-phase power provides smoother operation and requires smaller conductors for the same voltage and overall amount of power, it has all but replaced two-phase power. (Three-wire 120V/240V single-phase power in the United States is sometimes incorrectly called "two-phase.") U: A standard unit for designating the height of a computer, rack-mount server, or server blade chassis; 1U is equivalent to 44 millimeters or 1.75 inches, with multiples possible (2U, 3U, 4U and so on). UL: Underwriters Laboratories Underwriters Laboratories: UL is the nonprofit organization that operates a listing service for electrical and electronic materials and equipment in the United States. 42

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Shielded-type cable: A cable in which the conductors (wires) are enclosed in a conducting envelope
constructed so that virtually every point on the surface of the insulation is at ground potential.
Short circuit: An undesired electrical connection or crossover between two or more components (such
as a live wire touching a ground, a neutral wire, or a device’s metal casing).
Single-phase power: The 120V electric current that is standard in U.S. homes.
Spike: A brief instance of high voltage or current.
Supply air: The incoming air flow of air conditioning provided to cool a data center.
Surge: A sudden increase in voltage (volts) or current (amperes).
Surge protector: A protected power outlet that, when placed between electronic equipment and the
electric power supply, guards against a power surge by breaking the circuit.
Temperature rating: The maximum temperature at which an insulating material may be used in
continuous operation without loss of its basic properties, or the maximum temperature at which an
electrical device may be used in continuous operation without failure of its capacity specifications.
Terminal: Any device attached to the conductor (wire) by crimping, soldering or welding.
Three-phase power: The 120V/240V electric current that is standard in U.S. office buildings and data
centers.
Three-wire single-phase power: Commonly used in North America for single-family residential and
light commercial facilities. Three-wire single-phase power is sometimes incorrectly referred to as "two-
phase" power because it has two live conductors. A connection across two live wires delivers 240V
for heavy or heating appliances with less current and smaller conductors than necessary at 120V. No
individual conductor carries more than 120V over ground, so less insulation is required than for
single-ended 240V power.
Tolerance: The acceptable range of variance above or below the specified power rating or any other
standard or specification of measurement.
Transformer: An electrical device that transfers energy from one electrical circuit to another by
different magnetic couplings (ferrite coils or windings) without moving parts. A transformer is used to
convert between high and low voltages and between low and high currents. (If the voltage goes up,
the current must go down, and vice versa.) An alternating waveform applied to one winding induces
an alternating waveform in the other winding. As such, the transformer is an important element in the
transition (typically at efficiencies of 95 percent) between high-voltage power transmission via central
generating stations and low-voltage power used by homes and businesses.
Two-phase power: Used in some factories in the early 1900s, two-phase power was usually supplied
using four wires, two for each phase. (Less frequently, three wires were used, with a common wire
with a larger-diameter conductor.) Because three-phase power provides smoother operation and
requires smaller conductors for the same voltage and overall amount of power, it has all but replaced
two-phase power. (Three-wire 120V/240V single-phase power in the United States is sometimes
incorrectly called "two-phase.")
U: A standard unit for designating the height of a computer, rack-mount server, or server blade
chassis; 1U is equivalent to 44 millimeters or 1.75 inches, with multiples possible (2U, 3U, 4U and so
on).
UL: Underwriters Laboratories
Underwriters Laboratories: UL is the nonprofit organization that operates a listing service for electrical
and electronic materials and equipment in the United States.
42