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This glossary contains short defini-
tions of technical terms used in this
catalog. Because the terms used in
IEC/EN 60947 can be open to interpre-
tation, it is always advisable to also
refer to the relevant standard. This
applies in particular to the American
National Electrical Code (NEC,
NFPA 70) and the US standards
UL 508, UL 489, UL 508A, and NFPA 79.
The Canadian Electrical Code (CEC)
contains equivalent terms in standards
CSA-C 22.2 No. 5 and CSA-C 22.2
No. 14.
The American English terms are
appended to the glossary in a new
block. The German equivalents of the
American terms are not definitive
equivalents; they are intended merely
as an aid to understanding. Because
these terms often describe concepts
that are not defined in the IEC world,
there is no authorized German
equivalent for them. The explanations
apply to the use of components in
particular in industrial control panels
for machinery to UL 508A and NFPA 79.
Each technical term contains a
reference to the corresponding
standard, e.g. IEC/EN 60947-1. For the
correct translation, the IEV No. of the
electrotechnical glossary (IEC 50:
International Electrotechnical
Vocabulary) is specified,
e.g. IEV 441-17-31.
Altitude
The density of air decreases with increasing altitude, and this reduces its insulating
capacity as well as its heat transfer capability. This affects the rated operational
voltage and rated operational current of switching devices, conductors and motors,
as well as the tripping behavior of thermal overload relays. On request, Eaton can
supply information about the suitability of equipment for operation at altitudes
above the standard-specified 2000 m.
Ambient temperature, enclosed
(
cf. IEV 441-11-13) Temperature at which the switchgear is capable of being oper-
ated within a closed housing. The elevated temperature inside the enclosure due to
the switchgear's heat dissipation must be taken into account here.
Ambient temperature, open
(
cf. IEV 441-11-13) Room temperature (for example of the shopfloor or control room)
in which the switching device is located.
Auxiliary contact
(
IEC 60947-1/IEV 441-15-10) A contact which is included in an auxiliary circuit and is
mechanically operated by the switching device.
Auxiliary switch
(
IEC 60947-1/IEV 441-15-11) Switch containing one or more control or auxiliary con-
tacts and which is mechanically operated by a switching device. Auxiliary switches
can be retrofitted in modular systems of contactors, circuit breakers and motor-pro-
tective circuit breakers, or they are a fixed component of a switching device, e.g.
contactor relay.
They are designated according the functions
•
Making contact as a normally closed contact, normally open contact, change-
over contact or fleeting contact.
•
Function as normal, early, late, drive or trip indicator switches.
Back-of-hand proof
Switchgear is considered as back-of-hand proof if its conductive parts cannot be
touched with a ball with a diameter of 50 mm.
Busbar tag shroud
Design measures incorporated into equipment to prevent direct contact (i.e. with-
out tools) with live parts of a system (finger-proof, back-of-hand proof).
Clearance in air
(
cf. IEC/EN 60947-1; 2.5.46/IEV 441-17-31) The distance between the two conductive
parts at the point at which they are closest to each other. The clearance in air is
determined by the rated impulse withstand voltage, the overvoltage category and
the pollution degree.
Closing delay
The interval of time between the instant of command and the first make operation
of the contacts of the first pole to close. The closing delay is made up of the
response time and the closing time.
Control circuit reliability
The probability with which switching states arise during the lifespan of a contact
that would be interpreted as faults by downstream electronic controllers (PLCs).
Control circuit reliability is expressed in values based on tests using standard limit
values for signals to IEC/EN 61131-2.
Conventional thermal current I
th
(
cf. IEC/EN 60947-1; 4.3.2.1) The maximum value of current that a device is capable
of carrying for a maximum of 8 hours without thermal overloading. As a rule, it
corresponds to the maximum rated operational current.
Coordination type
State of a switchgear assembly (motor starter) during and after testing at rated
conditional short-circuit current:
Type “1” coordination:
-
No hazard to persons and systems.
-
No immediate operational readiness necessary.
-
Damage to the starter permissible.
Type “2” coordination:
-
No hazard to persons and systems.
-
Starter is suitable for further operation.
-
No damage to the starter except slight welding of the switch contacts if these can
be separated easily without significant deformation.
Creepage path/distance
(
cf. IEC/EN 60947-1; 2.5.51/IEV 151-03-37) Shortest distance between two conduct-
ing parts along an insulating material. Is determined by the material’s rated insulat-
ing voltage, the pollution degree and the creepage resistance.
Damp heat, constant
This test subjects the equipment to an ambient temperature of 40 °C at a constant
humidity of 93 %. At set intervals during the test, the electrical and mechanical
function of the equipment are examined.
Damp heat, cyclic
This test subjects the equipment to cyclically changing climatic conditions. A cycle
applies 40 °C at 93 % relative humidity for 12 hours, followed by 12 hours of 25 °C
ambient temperature. At set intervals during the test, the electrical and mechanical
function of the switching device are examined.
Emergency stop
(
cf. Machinery Safety Directive 2006/42/EC) Stopping in an emergency; an action
that stops a process or motion that causes danger.
Emergency stop system
Arrangement of components to avert arising or to reduce existing hazards to per-
sons, damage to machinery or to work in progress. The Emergency-Stop function
must be designed such that machine operation and dangerous machine motion are
halted in an appropriate manner without causing additional danger and without fur-
ther action being required from any person. (emergency stop function EN ISO 13850)
Emergency stop system
(
EN ISO 13850) Manually operated controlgear used for manually triggering an
emergency stop function.
Emergency switching off
Switches off the electrical energy supply to a complete installation or part of an
installation as soon as there is a risk of electric shock or an other risk caused by
electric current.
Finger-proof
A switching device is to be considered as finger-proof if its live parts cannot be
touched when actuating the operating elements. This also applies when operating
adjacent switchgear. The finger-proof area of a push-actuated operating medium is
a circular area of at least 30 mm radius around the actuating element, and vertical
to the direction of actuation. Within this area, hazardous parts should be fitted at
least 80 mm below the level of the actuating area.
Interlocked opposing contacts
(
cf. IEC/EN 60947-5-1, Appendix L) Combination of N/O and N/C contacts in contac-
tor relays that are mechanically connected in such a way that N/C and N/O can
never be closed at the same time. A contact spacing of at least 0.5 mm must be
maintained throughout the contacts’ entire lifespan, even in the event of a fault (for
example welded contacts).
Isolating function
(
cf. IEC/EN 60947-1; 2.1.19) Devices are deemed to possess this isolating function if,
in the open position, their switching contacts achieve the separation distance
specified for the isolation of electrical circuits, and their creepage paths and
clearance distances are of the required magnitude. This allows the power supply of
the entire installation or a section of the installation to be isolated for safety
reasons, for example during maintenance.
Losses
(
cf. IEV 151-03-18) The difference between the input power and the output power of
a device. The main type of loss in switching devices and electrical power distribu-
tion equipment is current heat loss.
Main switches
Correctly called “mains isolating device”. Hand-operatable switch. Mandatory for
machines with electrical equipment. Its purpose is to disconnect the electrical
equipment in order to exclude hazards occurring when cleaning, repairing or main-
taining the machine or during longer downtimes. A power disconnecting device
must:
•
Be an operating element that is externally accessible.
•
Have only one OFF and one ON position with assigned limit stops.
Glossary of terms
Terms from IEC and EN