Tap - A connection brought out of the winding at some point between its extremities, usually to permit changing the voltage or current ratio.

TCC (Time Current Curve) - TCCs are a series of points plotted in a curve on log paper describing the current-time reacting characteristics of a current interrupting device. TCCs are a tool used by engineers to determine coordination and correlation of devices.

Temperature Rise - The temperatures increase over ambient due to load.

Temporary Overvoltage (TOV) - A temporary overvoltage is define as an excursion of power frequency voltage above the normal line-to-ground value. Such excursions are of variable magnitude and duration.

Theatre - A building, or any portion thereof, which is used for public, dramatic, operatic, motion-picture, or other performances.

Thermal Cutout - A device affording protection from excessive current, but not necessarily short-circuit protection, and containing a heating element in addition to, and affecting, a fusible member which opens the circuit.

Three Phase Power - Three separate outputs from a single source. There is a phase difference of 120° between any two of the three voltages and currents.

Time Current Curves (TCC) - A series of points plotted in a curve on log paper describing the current-time reacting characteristics of a current interrupting device; a tool used by engineers to determine coordination and correlation of devices.

Time to Impulse Sparkover - The time between virtual zero of the voltage impulse causing sparkover and the point on the voltage wave at which sparkover occurs.

Tracking - Irreversible degradation of surface material from the formation of conductive carbonized paths.

Transformer - A static electrical device which by electromagnetic induction transfers electrical energy from one circuit to another circuit usually with changed values of voltage and current in the process.

Conventional - A transformer that has no protective equipment (fuses, breakers, arresters). They are used when the protective equipment is provided by a fuse cutout attached to the pole beside the transformer.

CSP (Completely Self-Protected) - A transformer that contains an internal breaker, an expulsion fuse and an arrester.

Dead Front - A transformer that has bushing wells and inserts or one-piece bushings used with elbows. The operator is not exposed to live parts.

Live Front - A transformer that has porcelain bushings with one or two hole spades or eyebolts from primary terminations. The operator is exposed to live parts.

Padmount - A transformer designed for mounting on a concrete pad with underground connecting cables.

Polemount - A transformer designed for mounting on a pole with overhead connecting lines.

Series Isolating - A transformer used in airport series lighting circuits to maintain continuity of
the primary circuit when the continuity of the secondary circuit is interrupted.

Transformer Rated Meter Mounting Device - a meter mounting device with current transformers and with or without test switches mounted in the same enclosure.

Transient - A high amplitude, short duration pulse superimposed on the normal voltage.

Transient Response - The ability of a circuit to faithfully reproduce a transient applied to its input.

Turn Ratio - The ratio of the number of turns in the high voltage winding to that in the low voltage winding.

Type I Nonmetallic Conduit - see definition for Conduit.

Type II Nonmetallic Conduit - see definition for Conduit.