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7. INTERNAL ARC CLASSIFICATION (IAC)
During development of all ABB products, focus is put on
personnel safety. This is why the SafeRing/SafePlus portfolio
was designed and tested for a variety of internal arc scenarios
in order to withstand an internal arc of the same current level
as a maximum short circuit current. The tests show that the
metal enclosure of Safering/SafePlus switchgear is able to
protect personnel standing close to the switchgear during an
internal arc fault.
Causes and effects of IAC
An internal arc is a highly unlikely fault, although it can theore-
tically be caused by various factors, such as:
− Insulation defects due to quality deterioration of the
components. The reasons can be adverse environmental
conditions and a highly polluted atmosphere.
− Inadequate training of the personnel in charge of the instal-
lation, leading to incorrect installation of the cables.
− Breakage or tampering of the safety interlocks.
− Overheating of the contact area, e.g. when the connections
are not sufficiently tightened.
− Short circuits caused by small animals that have entered
into the cable compartment (i.e. through cable entrance).
The energy produced by the internal arc causes the following
phenomena:
− Increase of the internal pressure.
− Increase of the temperature.
− Visual and acoustic effects.
− Mechanical stresses on the switchgear structure.
− Melting, decomposing and evaporation of materials.
Tested according to IEC standard 62271-200
The capability of SafeRing/SafePlus switchgear to withstand
an internal arc is proven by the type test according to Inter-
nal arc classification (IAC) as described in the standard IEC
62271-200 as follows:
Accessibility: A, B or C (switchgear)
A=Accessible to authorized personnel only
B=public access
C=not accessible due to installation
F-Front=Access from the front
L-Lateral=Access from sides
R-Rear=Access from the rear
All test specimens passed the following test criteria according
to the standards:
− Correctly secured doors and covers do not open
− No fragmentation of the enclosure occurs within the time
specified for the test. Projection of small parts, up to an
individual mass of 60 g are accepted
− Arcing does not cause holes in the enclosure of the switch-
gear up to a height of 2 m
− Indicators do not ignite due to the effect of hot gases
− The enclosure remains connected to its earthing point
Arc duration and damage caused
Melting of
Steel
Melting of
Copper
Melting of
Cables
0 100 200 500 ms
kA
2
s
R
L
L
F
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