Fast Speed Ratio - A speed ratio of melting
characteristics from 6-8 (refer to Speed Ratio).
Fault Close Rating - The ability of a switching
device to close into a fault current of a specific magnitude without
Fault Current - The current from the connected
power system that flows in a short circuit.
Fault Indicator- A device which indicates fault
current by sensing the magnetic field caused by current flowing
through the conductor. Once the current is above the fault indicator's
current rating, the fault indicator will trip.
Feeder - Any portion of an electrical circuit
between the service box or other source of supply and the branch
circuit overcurrent devices.
Ferroresonance - A phenomenon characterized by
overvoltages and very irregular wave shapes which are potentially
damaging to a transformer. It typically occurs when there is no
ground on the system except through the transformer connected line
to ground. It is always associated with the excitation of one or
more saturable inductors through capacitance in series with the
inductor. When one or two phases are disconnected from the source
by single-pole fault clearing or switching, it is possible for
the transformer windings connected to the open phases to be excited
through the system capacitances to ground and between phases.
Fire-Resisting when Applied to a Building - Means
constructed of masonry, reinforced concrete, or equivalent materials.
Flashover - A disruptive discharge around or
over the surface of an insulator.
Flat Conductor Cable Type FCC - the following
special terminology applies to the installation of
Type FCC under-carpet wiring systems:
- Bottom shield - a protective layer that is between the floor
and the Type FCC cable to protect the cable from
- Insulating end - an insulator designed to electrically
insulate the exposed ends of Type FCC cables.
Metal tape - a metal overlay to prevent physical damage to
the Type FCC system.
- Top shield - an electrically conductive covering
for under-carpet components of a Type FCC system that
provides a degree of protection against physical damage
and electric shock and may or may not be incorporated
as an integral part of a Type FCC cable assembly.
assembly - an assembly specifically approved for the purpose
of connecting a Type FCC system
to other types of wiring systems.
- Type FCC cable - a cable
consisting of 3 or more flat separated conductors laid flat
and parallel in the same
plane and enclosed within an insulating assembly.
- Type FCC
cable connector - a device used for joining Type FCC cables,
with or without the use of a junction
- Type FCC system - a complete wiring system for installation
only under carpet squares and includes cable and
Flexible Metal Conduit - A metal conduit that
may be easily bent without the use of tools.
Flicker - Impression of fluctuating brightness
or color, occurring when the frequency of the observed variation
lies between a few hertz and the fusion frequencies of the images.
Fluctuation - A surge dip in voltage amplitude,
often caused by load switching or fault clearing.
Follow Current - The current which flows through
an arrester, caused by the power frequency voltage across it, during
and after the passage of surge current.
Frequency - On ac circuits, the designated number
of times per second that polarity alternates from positive to negative
and back again, expressed in Hertz (Hz)
Fulgurite - tunnel-like structure formed when
a current-limiting fuse operates; glass-like structure formed by
the temperature of a high voltage arc when a current-limiting fuse
operates; the fused silica sand that remains after prolonged abnormal
Fuse - A device that will heat up, melt and electrically
open the circuit after a period of prolonged abnormal current flow.
Fuse Arcing Time - The amount of time required
of the fuse to extinguish the arc and clear the circuit; the specific
amount of time required for an interrupter to clear a circuit after
its fusible element has melted.
Fuse, Buttonhead - A relatively common type of
expulsion fuse utilized in open or enclosed cutouts; the name given
to the upper assembly of a distribution fuse link which is then
used in a reusable fuseholder for outdoor cutout applications.
Fuse Canister - Dry well full range current-limiting
fuse holder - loadbreak and non-loadbreak. Fuses are mounted in
an oil tight canister which extends into the tank beneath the oil.
Accessible from the high voltage compartment, the fuse is air insulated.
Fuse, Cartridge - Expulsion type fuse with either
current sensing or dual (current and oil temperature) sensing elements
mounted internally under-oil. Used to remove an apparatus from
the primary circuit in the event of a current fault. Cartridge
fuses have limited interrupting ratings.
Fuse Clearing Time - The total time required
for the fuse to melt and clear the circuit; melting time plus arching
Fuse, Clip-Mounted - A full range current-limiting
fuse mounted in clips in the high voltage compartment.
Fuse, Current Sensing - An expulsion fuse having
elements whose characteristics are not affected by elevated oil
temperatures; a fuse having elements that are made of copper, tin
or silver that will react to current flow only.
Fuse, Dual Sensing - An expulsion transformer
fuse having elements that are sensitive to fault current, load
current and temperature (top oil); a fuse that senses the top oil
temperature of a transformer in addition to the temperature from
the current flow; a fuse that can monitor the aging effects of
elevated transformer hot spot temperatures regardless of cause;
sometimes know as "load" sensing.
Fuse, Electric - An overcurrent protective device
with a circuit opening fusible part that is heated and severed
by the passage of overcurrent through it.
Fuse, Expulsion - A replaceable one-shot current
interrupting device having definite time current characteristics;
a device which has a metal melting element and uses the principles
of heated fibers releasing de-ionizing gases, and alternating current
passing through a zero reference periodically for arc extinction.
Fuse Link - The (metal) fusible element in an
expulsion cutout; the composite construction of materials that
house the fusible element.
Fuse Maximum Interrupting Current - That upper
current level that a fuse can successfully clear with assured reliability;
the maximum current at a specified maximum design voltage that
a fuse if required to clear as specified by the manufacturer.
Fuse Maximum Operating voltage - The maximum
voltage that a fuse can properly operate at with assured clearing.
Fusing Melting Time - The amount of time required
to melt a fusible element at a specific current.
Fuse Minimum Interrupting Current - That lower
limit of current that up0on melting a fuse can be assured of successfully
clearing; a term generally associated with back-up current-limiting
fuses indication the lower limit of current that the fuse can clear
Fuse, Open-Link - An outdoor expulsion fuse for
use in an open-link cutout; a one-shot fuse that is usually suspended
between two spring arms which hold the link in tension; a "flipper" fuse.
Fuse, (silver) Sand - An abbreviated name for
a type of current-limiting fuse that has silver for its element
and sand as its surrounding media (refer to Current-Limiting Fuse).
Fuse Spider - The element support material used
in a current-limiting fuse of various compositions and design.
Fuse, Type D - Refer to D-Link.
Fuse, Type K - A specific type of expulsion fuse
available in button and open-link configurations. The "K" designation
refers to specific time current characteristics, defined by ANSI,
allowing customers to purchase fuses from more than one manufacturer
without adversely affecting the overall operation of the system.
Fuse, Type N - Expulsion fuse links having time
current characteristics unique to and defined by individual fuse
manufacturers. Since the characteristics are unique, various manufacturers'
products cannot be interchangeably used on a distribution system
without adversely affecting its operation. In addition to type "N",
other links that fall into this category are Type H, Type Q, Type
QA, Type KS, Type 200, etc.
Fuse, Type T - A specific type of expulsion fuse
available in button and open-link configurations. The "T" designation
refers to specific time current characteristics as defined by ANSI.
In reference to the type "K" links, the type "T" links
are time delayed or retarded in operating characteristics.
Fuse, Weak Link - A coined name for the cartridge
fuse. The name is take from the thought that the fuse would be
the weakest link in a chain causing the fuse to open the circuit
before equipment is damaged.