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Appendix
Glossary
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Degree of pollution
A conventional classification for the degree of pollution to be ex-
pected in the micro-environment. Pollution refers to any foreign,
solid, liquid or gaseous substance that might change the voltage
endurance or surface resistance.
Degree of protection
The degree of protection of a device specifies the scope of pro-
tection. The scope of protection comprises the protection of per-
sons against contact with live parts and the protection of electri-
cal devices against the penetration of foreign bodies and water
by means of enclosures and encapsulation.
The degree of protection is expressed internationally by a com-
bination of letters (IP = International Protection) and numbers.
The first number defines the degree of contact and foreign body
protection, the second the water protection.
Dynamic short-circuit strength
Mechanical strength against short-circuit loads at switching de-
vices and particularly for busbars in switchgear assemblies and
distribution boards. (Short-circuit strength)
Electric arcs
Sparking that always occurs when an electrical circuit is turned
on at voltages > 15 V. The strength of the arc depends
on, among other things, the type and level of the load, the power
factor, as well as the phase relation of the voltage curve at the
instant of the contact separation. Temperatures of 10 000 °C to
15 000
°C can occur at the center of an arc, which may cause
the contact material to vaporize. Because the electric arc has a
direct influence on the service life of the contact, it is essential to
take measures to ensure that the arc is kept small and/or that it
is extinguished as quickly as possible.
Electromagnetic compatibility (EMC)
Electromagnetic compatibility (EMC) is the ability of an electrical
device to function perfectly in its electromagnetic environment,
i.e. without being unacceptably influenced by it or vice versa.
Encapsulation
Enclosure for the protection of electrical devices. If offers en-
closed equipment protection against harmful environmental in-
fluences (degrees of protection) and protection against direct
contact (protective measures).
Enclosure
Component that protects the equipment against certain external
influences and which offers degree of protection of at least IP 2X
against direct contact from any direction.
Equipment (electrical)
Technical products or their components insofar as their function
and design serve the use of electrical energy. This includes
products that generate, transmit, distribute, store, measure,
monitor, control or convert electrical energy.
EVU / VNB
German abbreviation for electric utility companies, i.e. the pro-
viders of electrical energy (power stations).
Fault current (differential current)
A fault current is the current that flows due to an insulation fault.
For example, it is measured as the differential between the cur-
rents flowing into the system over a measuring device and those
flowing out over the same device (DIN VDE 0664).
Fault voltage
Voltage that occurs between exposed, conductive components
that do not belong to the main circuit, or between these compo-
nents and the earth. Persons coming into contact with faulty ma-
chines or plants who are also, for example, standing on conduc-
tive flooring, will be subjected to a partial fault voltage, the so-
called touch voltage.
Function classes
These specify which current range the fuse link can switch off
(
operational classes).
Functional extra-low voltage
Protective measure, during which the circuits are operated with
a rated voltage of up to 50 V alternating voltage or 120 V direct
voltage, but which do not fulfill the requirements of safety extra-
low voltage (SELV) and are therefore subject to further condi-
tions. With functional extra-low voltages, a distinction is made
between with and without safe isolation.
Fuse
Protective device that serves to open the circuit in which it is in-
stalled if the current exceeds a specified value for a prescribed
duration. It does this by melting one or more fuse elements, thus
interrupting the current in accordance with the respective trip-
ping characteristic.
Note:
The fuse covers all components that are part of the complete
protective device.
Fuse element
Specially shaped conductors made of copper (in special cases
of silver) in the fuse body of the fuse link. It melts in the case of
overloads or short circuits due to joule heat. Key features are the
solder area and limiters. The solder area melts in the event of a
non-permissible overload, the limiters are defined fusing points
in the event of short circuits.
Fuse link
The fuse link is the part of the fuse that holds one or more fuse
elements and which must be replaced after the fuse has been
tripped in order to restart the device. The current interruption
and all associated actions are carried out inside an enclosed
melting chamber filled with quartz sand.
Ground
Designation for the conductive earth whose electrical potential is
set to zero. According to DIN VDE 0100 Part 200 the word
ground is the designation for the place as well as the material.
Group p.f. correction
With group p.f. correction, the correction device is assigned a
load group. This may comprise motors or fluorescent lamps that
are connected to the system over a common contactor or other
switching devices.
Impedance (Z)
Impedance (Z) is the sum of the resistors in a circuit at the rated
current. It is made up of the resistance (R) and inductive resis-
tance/reactance (
).
The specified values refer to the rat-
ed frequency.
Individual p.f. correction
For individual p.f. correction, the capacitors are connected di-
rectly to the terminals of the individual loads and switched on to-
gether with these over a common switching device.
Inherently ground-fault-proof
Equipment or conducting paths are inherently earth-fault-proof
when, through the application of suitable measures under pre-
scribed operating conditions, no ground faults (short-circuits to
frame) are to be expected (inherently short-circuit-proof).
Inherently short-circuit-proof
Equipment or conducting paths are inherently short-circuit-proof
when, through the application of suitable measures under pre-
scribed operating conditions, no short-circuit faults are to be ex-
pected (inherently short-circuit-proof).
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© Siemens AG 2008