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T - Z

T      [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z]

Technician - Refers to an electronic technician qualified to maintain and repair electronic equipment. Not necessarily qualified to install electrical wiring. Compare to Electrician.

Temperature Derating - Reducing the overall capacity of a power supply to account for an elevated temperature ambient. See Derating.

Terminal Block - An insulating base equipped with terminals for connecting secondary and control wiring. Used on hardwired equipment, such as a UPS, when input plugs and output receptacles are either impractical or unavailable.

Terminal - A connector for attaching a conductor to an electrical apparatus.

Thermal Protection - A device or circuit designed to protect the equipment from damaging temperatures. Some UPS and PDUs are capable of doing this for their connected loads.

Three-Phase Power (3Ø) - Power that is provided by a single source with three outputs with a phase difference of 120° between any two of the three voltages and currents.

Toroidal Inductor - An inductor constructed by placing a winding(s) on a core that has a donut shaped surface. Toroidal cores are available in many magnetic core materials within the four basic types: Ferrite, Powdered iron, Alloy and High Flux, and Tape Wound. Characteristics of toroidal inductors include: self shielding (closed magnetic path), efficient energy transfer, high coupling between windings and early saturation.

Total Harmonic Distortion (THD) - The square root of the sum of the squares of the RMS harmonic voltages or currents divided by the RMS fundamental voltage or current. Typically a supply sine wave is considered acceptable when THD levels are 5% or less. See harmonics, harmonic distortion and distortion. Can also be calculated in the same way for only even harmonics or odd harmonics.

Transducer - A device that senses one form of energy and converts it to another, i.e., temperature to voltage (for monitoring).

Transfer Switch - A switch which will transfer current from one circuit path to another without interrupting the flow of the current. A switch used to transfer a load between a UPS and its bypass source.

Transfer Time - The amount of time it takes to sense a power failure and to switch the load to inverter power. Applicable to standby or offline UPS units. True online UPS do not have an interruption in the power to the load.

Transformer - (T) A device that raises or lowers the voltage of an alternating current electrical source.

Transient - The fast radical change in a smooth sine wave that occurs in both voltage and current waveforms during the transition from one steady-state operating condition to another. Transients take place when there is a rapid voltage peak of up to 20,000 volts with a duration of 10 microseconds to 100 microseconds. They are commonly caused by arcing faults and static discharge. In addition, major power system switching disturbances initiated by the utilities to correct line problems may happen several times a day. Effects can include memory loss, data error, data loss and component stress.

Transient Response Time - The time from a step change in load, voltage or other parameters until the power supply output recovers to nominal specification.

Transient Suppression - See Surge Suppressor.

Transverse Mode Noise - Normal mode. An undesirable voltage which appears from line to line of a power line.

Transverse Mode Noise Rejection (TMNR) - The ability of an electronic device, like a UPS, to block transverse mode noise between input and output.

Trickle Charging - With the trickle charging process, the battery receives a constant voltage feeding a low current. Constant use of this method dries the electrolyte and corrodes the plate, reducing potential battery service life by up to 50 percent.

Two-Phase Power (2Ø) - Power which is provided by a single source with two outputs which may be 180 degrees out of phase or 120 degrees out of phase.

Turns Ratio - The ratio of the primary voltage (or turns) to the secondary voltage (or turns) in a transformer.

TÜV - A European safety agency that sets standards for product safety. See CE, UL, ETL, CSA and VDE.

TVSS - Acronym for Transient Voltage Surge Suppressor. Another term for surge suppressor taken from the UL designation for this type of product. See Surge Suppressor.

U      [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z]

xU - x Rack Units. Each Rack Unit is 1.75 inches in height. Width depends on the rack width, i.e. 19 or 23-inch width. Most rack equipment panel heights are in full rack units, not fractional, i.e. 3U.

UL - Underwriter’s Laboratories, Inc. A US independent safety agency that sets standards for product safety. See ETL, CSA, CE, VDE and TÜV.

UL Listed - A UL Listed product has met to applicable UL Standard for that class of equipment. Listed products are typically end products and not components.

UL Recognized - A UL Recognized device has met to applicable UL Standard for that class of device. Recognized components are typically parts that go into making the finished product.

Undervoltage - By definition, it is voltage at 90% or less of the normal level for more than one minute.  Sometimes it is called a brownout.

UPS - Uninterruptible Power Supply or System or Source. A system designed to automatically provide power, without delay or transients, when the normal power supply is incapable of supplying acceptable power. Some UPSs also filter and/or regulate utility power.

UPS Topology - Overall term describing the internal circuitry of a UPS. There are three basic UPS topologies: standby (off-line), line-interactive, and online.

User-Replaceable Batteries - User replaceable batteries allow the user to easily exchange UPS batteries, once the unit has been turned off.

V      [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z]

VA - Volt-Amperes, product of volts times amperes, vectorial sum of Watts and VARs. Voltage (V) multiplied by the current (ampere); apparent power. For instance, a device rated at 10 amps and 120 V has a VA rating of 1200 or 1.2 kVA.

VAC - Voltage Alternating Current. The voltage measurement in an AC system.

VAR - Volt-Ampere Reactive, the reactive component of the VA.

VDC - Voltage Direct Current. The voltage measurement in an DC system.

VDE - A European safety agency that sets standards for product safety. See CE, UL, ETL, CSA and TÜV.

Voltage (volt or V) - The International System of Units measure of the potential difference between two electrical points, i.e. between line and neutral conductors. Voltage is the electrical pressure which forces the current to flow in a conductor such as a wire.

W      [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z]

WAN - Wide Area Network. A network which encompasses interconnectivity between devices over a wide geographic area.

Watt (W) - The unit of power in the International System of Units equivalent to 1 joule per second. The unit of measure for true power. Watts = VA x Power Factor

Watt-hour (Wh) - Electrical energy equivalent to 1 watt acting for 1 hour. This is also equivalent to 3.4136 BTUs (1 watt-hour = 1 joule/second x 3600 seconds/hour x 1 BTU/1054.6 joules = 3.416 BTUs).

WYE (Y) Connection  - A three-phase source of load connection, with a single common junction and three phase lines out or in.

X      [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z]

Y      [A B C D E F G H I J K L M N O P Q R S T U V W XY Z]

Z      [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z]

Zero Voltage Switching (Zero Crossing Switching) - Technique in which the power switch in a converter turns on and off when there is a zero voltage across it. This minimized switching transient noise output from the converter.