Use the links below to view the aphabetical listing of terms and definitions used on this site
A
accessory = An electrical or mechanical
device that performs a secondary or minor function apart from overcurrent
protection.
accessory cover = A removable cover on the front of a circuit breaker
behind which are mounted the trip unit and all electrical accessories.
adjustable rating plug = A component which plugs into the trip unit, establishing
the ampere rating of the circuit breaker
AIC = Amperes interrupting capacity.
AIR = See amperes interrupting rating.
alarm switch (bell alarm) = See overcurrent
trip switch.
ambient temperature rating = Temperature
at which the continuous current rating (handle rating) of a circuit breaker
is based; the temperature of the air immediately surrounding the circuit
breaker which can affect the thermal (overload) tripping characteristics
of thermal-magnetic circuit breakers. Electronic trip circuit breakers,
however, are insensitive to normal (-10° to 50°C) ambient conditions.
ammeter (local current meter) = A module
that mounts directly to the circuit breaker trip unit and reports RMS
phase and ground fault current values as seen by the trip unit. Current
values are displayed one phase at a time.
ampacity = The current, in amperes, that
a conductor or circuit breaker can carry continuously under the conditions
of use without exceeding its temperature rating.
ampere = The equivalent of one coulomb per
second or the steady current produced by one volt applied across a resistance
of one ohm.
amperes interrupting rating = The highest current at rated voltage that
an overcurrent protective device is intended to interrupt under specified
test conditions (NEC).
ANCE (National Association of Standardization and
Certification for the Electrical Sector) = The standards and certification
agency accredited by the Mexican government.
ANSI® = American National Standards
Institute.
automatic molded case switch = A switch with construction similar to a
molded case circuit breaker except that the switch opens only instantaneously
at a non-adjustable trip point calibrated to protect only the molded case
switch itself.
auxiliary switch = A switch mechanically
operated by the main device for signaling, interlocking, or other purposes.
B
bell alarm = A mechanically-operated switch used to indicate the
main contact position of a circuit breaker, which indicates when a circuit
breaker has tripped. Also see overcurrent trip switch.
BPFE = See electrical closing push button.
branch circuit = The circuit between the
final overcurrent device protecting the circuit and the outlet(s).
BCM = See circuit breaker communications
module.
C
Canadian Standards Association® (CSA®) = Canadian product
safety testing and certification organization.
circuit breaker = A device designed to open
and close a circuit by nonautomatic means and to open the circuit automatically
on an overcurrent without damage to itself when properly applied within
its rating.
circuit breaker communications module (BCM) = A module which, when installed
in a circuit breaker, receives and transmits information on the communication
network.
circuit breaker frame = (1) The circuit
breaker housing which contains the current carrying components, the current
sensing components, and the tripping and operating mechanism. (2) That
portion of an interchangeable trip molded case circuit breaker remaining
when the interchangeable trip unit is removed.
close button = A button for manually closing
the main contacts after the closing springs are charged.
close button cover = A cover which fits
over the close button and blocks access to it. Access to the close button
may be permitted through the use of a tool or rod inserted through a small
hole in the front of the close button cover.
closing coil (shunt close) = A coil which
closes the circuit breaker electrically using an external voltage source
when a specified voltage is applied across the coil.
coil clearing switch = A mechanically-operated
switch in series with the coil of a shunt trip device which breaks the
coil current when the circuit breaker opens.
combination motor controller = One or more
devices assembled to provide disconnecting means, branch circuit protection,
motor control, and motor overload protection for a single motor circuit.
communication network = A network allowing
the flow of information between electrical components, comprised of programmable
controller interface units, protocol software and modems.
conductor = A substance or body that allows
a current of electricity to pass continuously along it.
continuous current rating (handle rating) (ampere
rating) = The designated RMS alternating or direct current in amperes
which a device or assembly will carry continuously in free air without
tripping or exceeding temperature limits.
continuous load = A load where the maximum
current on the circuit is expected to continue.
control circuit = A circuit that carries
the electric signals directing the performance of a controller, and which
does not carry the main power circuit. A control circuit is, in most cases,
limited to 15 amperes.
control transformer = A transformer whose
secondary supplies power to control circuit devices only (excluding loads).
cradle communications module (CCM) = An
external module which allows addressing of the cradle and retention of
the address when the drawout circuit breaker is in the disconnected position
and which is used to transmit information about the position of the circuit
breaker in the cradle to the communication network.
cradle compartment = A compartment containing
all connectors, shields, adapters, barriers, spreaders, shutters, keys
and interlocking devices for a drawout circuit breaker.
CSA® = See Canadian Standards Association.
CT = Current transformer. See also cell
switch.
current path (of a circuit breaker) = The current-carrying conductors
within a circuit breaker between, and including, line and load terminations.
current transformer (current sensor) (CT)
= An instrument to measure current, encircling a conductor carrying the
current to be measured or controlled.
D
demand metering = The metering of power
or current demand seen by a circuit breaker. It is calculated over a fixed
or sliding time window that can be programmed from five to 60 minutes.
Depending on the contract signed with the power supplier, specific programming
makes it possible to avoid or minimize the cost of overrunning the subscribed
power. Maximum demand values are systematically stored and time stamped.
disconnecting contacts = See main disconnecting
contacts and secondary disconnecting contacts.
drawout circuit breaker = An assembly of
a circuit breaker and a supporting structure (cradle) so constructed that
the circuit breaker is supported and can be moved to either the main circuit
connected or disconnected position without removing connections or mounting
supports.
drawout mechanism = A mechanism which engages
the drawout cradle assembly and draws the circuit breaker into or out
of the switchboard. The drawout mechanism includes the drawout mechanism
shaft, drawout levering device arms and a drawout position indicator.
drawout position indicator = An indicating
means which shows the position of the circuit breaker in the drawout structure.
drawout access cover (drawout shaft cover)
= A shutter which allows or restricts access to the drawout shaft.
E
electrical closing push button (BPFE) = A push button used to electrically
close a circuit breaker using a shunt close with communication option.
This takes into account all safety functions that are part of the control
and monitoring system of the installation.
electrical operator (motor operator) = An
electrical device used to open and close a circuit breaker or switch and
reset a circuit breaker. See also spring charging motor.
electronic trip circuit breaker = A circuit
breaker which uses current sensors and electronic circuitry to sense,
measure and respond to current levels.
F
feeder circuit =The conductors and circuitry on the supply side
of the branch circuit overcurrent protective device.
fixed-mounted circuit breaker = A circuit breaker so mounted that
it cannot be removed without removing primary and sometimes secondary
connections and/or mounting supports.
frame size = The largest ampere rating available
in a group of circuit breakers of similar physical configuration.
frequency = The number of cycles per second
for an alternating current system.
frequency rating = The range of frequencies
within which a product can be applied.
G
ground fault = An unintentional current path, through ground, back
to the source.
ground fault delay = The length of time
the circuit breaker trip unit will delay before initiating a trip signal
to the circuit breaker after a ground fault has been detected.
ground fault module = An electronic accessory
used in combination with thermal-magnetic circuit breakers to provide
branch circuit ground fault protection and ground fault indication.
ground fault pickup = The level of ground
fault current at which the trip system begins timing.
H
handle rating = Continuous current rating.
I
IDMTL = Long-time delay curve which can be varied in slope to enhance
selectivity.
IEC® = International Electrotechnical
Commission.
IEEE® = Institute of Electrical and
Electronics Engineers.
Ig = See ground fault pickup.
Ii = See instantaneous pickup.
In = See sensor rating.
individually-mounted circuit breaker = A
circuit breaker so mounted that it cannot be removed without removing
primary and sometimes secondary connections and/or mounting supports.
industrial control panel for general use
= A control panel intended to be installed in accordance with the general
use requirements in Chapter 4 of the National Electrical Code, ANSI/NFPA
70.
instantaneous pickup = The current level
at which the circuit breaker will trip with no intentional time delay.
instantaneous trip = A qualifying term indicating
that no delay is purposely introduced in the tripping action of the circuit
breaker during short-circuit conditions.
insulated case circuit breaker (ICCB) =
UL Standard 489 Listed nonfused molded case circuit breakers which utilize
a two-step stored energy closing mechanism, electronic trip system and
drawout construction.
integral ground fault protection for equipment = Equipment ground fault
protection on grounded neutral systems provided by components internal
to the circuit breaker.
interchangeable trip unit = A trip unit
which can be interchanged by a user among circuit breaker frames of the
same design.
interrupting rating = The highest current
at rated voltage available at the incoming terminals of the circuit breaker.
When the circuit breaker can be used at more than one voltage, the interrupting
rating will be shown on the circuit breaker for each voltage level. The
interrupting rating of a circuit breaker must be equal to or greater than
the available short-circuit current at the point at which the circuit
breaker is applied to the system.
inverse time = A qualifying term indicating there is purposely introduced
a delay in the tripping action of the circuit breaker, which delay decreases
as the magnitude of the current increases.
J
K
L
Ir = See long-time pickup.
Isd = See short-time pickup.
I2t = See let-through current.
I2 t IN (I2 t ON) = An inverse time delay
characteristic.
I2 t OUT (I2 t OFF) = A constant time delay
characteristic.
let-through current = The peak current (measured
in amperes) which passes through an overcurrent protective device during
an interruption.
let-through I2t = An expression related
to energy (measured in ampere-squared seconds) which passes through an
overcurrent protective device during an interruption.
limit switch = A switch mechanically operated
by a device.
long-time ampere rating = An adjustment
which, in combination with the installed rating plug, establishes the
continuous current rating of a full function electronic trip circuit breaker.
low voltage power circuit breaker (LVPCB)
= A circuit breaker tested to the ANSI C37 Standards with a two-step stored-energy
mechanism, an electronic trip system, and drawout construction.
M
main disconnecting contacts = Spring-loaded and self-aligning contact
on the rear of a drawout circuit breaker that provide positive electrical
contact when the circuit breaker is in the connected position.
MRO = Maintenance, Repair and Operations
– a classification of an industrial function
MASTERPACT® = The family of universal
power circuit breakers including insulated case circuit breakers and low-voltage
power circuit breakers.
MICROLOGIC® = The family of electronic
trip systems available on molded case circuit breakers, insulated case
circuit breakers and low-voltage power circuit breakers.
miniature circuit breaker (MCB) = A small
circuit breaker which is assembled as an integral unit in a supportive
and enclosed housing of insulating material, rated 150 A or less and used
in 120 V, 120/240 V, 240 V and 480Y/277 V ac systems and dc systems up
to 125 Vdc.
MN = See undervoltage release.
MODBUS® communication network = A communication
network comprised of programmable controller interface units, protocol
software and modems.
molded case circuit breaker (MCCB) = A circuit
breaker which is assembled as an integral unit in a supportive and enclosed
housing of insulating material, generally 20 to 3000 A in size and used
in systems up to 600 Vac and 500 Vdc.
motor circuit protector = A recognized component
of construction similar to a circuit breaker except with no thermal elements
so that it provides shortcircuit protection only.
MX = See shunt trip.
N
National Association of Standardization and Certification
for the Electrical Sector = See ANCE.
NFPA = National Fire Protection Association
– primary sponsor of the National Electrical Code.
NEC = National Electrical Code – Guidelines
for electrical installation processes and procedures. Produced by the
National Fire Protection Association.
NEC ARTICLE 409 = Specific National Electrical
Code Article referencing Industrial Panel electrical requirements
neutral current transformer = A current
transformer which encircles the neutral conductor; required on circuit
breakers with ground fault protection, when applied on a grounded system.
NMX® (Norma Mexicana X) = Listing mark
indicating certification to nonmandatory Mexican safety standards.
NOM = Listing mark indicating certification
to mandatory Mexican safety standards
O
OF = See auxiliary switch.
open/closed indicator = An indicating means
which displays the position (open or closed) of the main contacts.
open industrial control panel = An industrial
control panel that includes internal wiring, field wiring terminals, and
components mounted on a sub-panel without a complete enclosure. The enclosure
is intended to be supplied/completed at the installation.
operating mechanism = An internal mechanical
system which opens and closes the circuit breaker contacts.
OTS = Overcurrent trip switch (alarm switch,
bell alarm). A mechanical switch that operates when the circuit breaker
is tripped by the trip system.
overcurrent = Any current in excess of the
rated continuous current of equipment or the ampacity of a conductor.
overcurrent mechanism = An internal mechanical
system which trips the circuit breaker during an overcurrent.
overcurrent trip element = A device which
detects an overcurrent and transmits the energy necessary to open the
circuit automatically (UL only).
overload delay = The length of time the
circuit breaker will carry a sustained low-level overcurrent before initiating
a trip signal.
P
peak current sensing = A method of determining the current by means
of detecting the current peaks.
peak let-through current = The maximum peak
current flowing in a circuit during an overcurrent condition.
phase barrier = A barrier which provides
phase-to-phase or phase-to-ground isolation.
power circuit = Conductors and components
of branch and feeder circuits.
POWERLOGIC® = The family of electronic
circuit monitoring systems available on molded case circuit breakers,
insulated case circuit breakers and low-voltage power circuit breakers.
POWER-ZONE® = The family of low-voltage
and medium-voltage switchgear.
programmable contact module (M6C and M2C)
= A programmable module which indicates the type of fault and the instantaneous
and delayed threshold overruns. It may be programmed with instantaneous
return to the initial state, without return to the initial state, or with
return to the initial state following a delay.
Q
R
RMS = Root-mean-square.
RMS current sensing = A method of determining
the true RMS current of sinusoidal and non-sinusoidal waveforms by sampling
the current waveform a number of times per cycle, then calculating the
true RMS value.
S
safety shutter = A device that closes to block access to the main
disconnects when the circuit breaker is in the disconnected, test or withdrawn
position.
SCCR = Short Circuit Current Rating
SDE = See overcurrent trip switch.
secondary disconnect contacts = An electrical
plug-on connector in the secondary (control) circuit between a drawout
circuit breaker and its cradle in the switchboard or switchgear.
sensor = The current sensing element within
the circuit breaker which provides the sensing function for that circuit
breaker.
sensor plug = A component used with the
MICROLOGIC trip system to set the sensor size of a circuit breaker.
sensor size = Maximum ampere rating possible
for a specific circuit breaker, based on the size of the current sensor
inside the circuit breaker. Sensor size is less than or equal to frame
size.
SGR = Source ground return system.
short-circuit delay (STD) = The length of time the circuit breaker will
carry a short circuit (current greater than the short-circuit pickup)
before initiating a trip signal.
short-circuit pickup = The current level at which the circuit breaker
shortcircuit delay function begins timing.
STD = Short-time delay.
supplementary protection = A device intended
to provide additional protection subsequent to branch circuit protection.
They have not been evaluated for providing branch circuit protection.
supplementary protector = A manually resettable
device designed to open the circuit automatically on a predetermined value
of time versus current or voltage within an appliance or other electrical
equipment. It is also able to be provided with manual means for opening
or closing the circuit. These devices are able to provide supplementary
protection only.
T
terminal block = The connections for control wiring.
tg = See ground fault delay.
thermal imaging = A trip unit function that
accurately maps the heating and cooling effects of load behavior on rated
conductors to provide thermal protection without nuisance tripping.
thermal-magnetic circuit breaker = A general
purpose term for circuit breakers that use bi-metals and electromagnetic
assemblies to provide both thermal and magnetic overcurrent protection.
thermal memory = Provides continuous temperature
rise status of the wiring for a period of time both before and after the
device trips. This allows the circuit breaker to respond to a series of
overload conditions which would otherwise go undetected.
transformer = A static device with primary
winding, connected in series with the conductor (bus) carrying the current
to be measured or controlled within the switchgear.
trip curve = A graphical representation
of the response of a circuit breaker to current over a period of time.
trip indicator = A module that mounts directly
to the circuit breaker trip unit that displays whether the circuit breaker
tripped due to an overload, a shortcircuit or a ground fault condition.
trip indicator reset = A button on the trip
indicator module used to reset the trip indicator.
trip system = A system which consists of
a MICROLOGIC trip unit and current transformers.
trip unit = A programmable device which
measures and times current flowing through the circuit breaker and initiates
a trip signal when appropriate.
U
UL® = See Underwriters Laboratories
Inc.
UL 508A = Specific Underwriters Laboratories
standards referencing SCCR calculations to obtain the NEC 409 rating for
Industrial Control Panels.
Underwriters Laboratories Inc.® (UL®) = An independent, not-for-profit
standards development, product safety testing and certification organization.
V
W
withstand rating = The level of RMS symmetrical current that a
circuit breaker can carry with the contacts in a closed position for a
stated period of time–usually stated in cycles.
Y
Z
zero-blind time = Metering method used by the MICROLOGIC® H
trip unit where a dedicated metering data chain is separate from the protection
data chain so that a greater number of data samples can be used for metering.
This increases the number of samples taken per time period, which in turn
gives the H trip unit a higher degree of metering accuracy.
zero-sequence ground fault sensing = A means
of providing equipment ground fault protection utilizing an external sensor
(surrounding all phase and neutral conductors).
zone-selective interlocking (ZSI) = A communication
capability between electronic trip systems and ground fault relays which
permits a short circuit or ground fault to be isolated and cleared by
the nearest upstream device with no intentional time delay.
ZSI = Zone-selective interlocking.
Electrical equipment should be installed, operated, serviced, and maintained only by qualified personnel. No responsibility is assumed by Schneider Electric for any consequences arising out of the use of this material.