MANUAL MOTOR STARTER GUIDE
APRIL 19
17/80
2.2 Terms and ratings
2.2.1 Rated operational voltage (U
e
)
The rated operational voltage of a manual motor starter is a value of phase-to phase voltage which determines the
possible application of the manual motor starter. This voltage needs to be considered in combination with a rated
operational current.
2.2.2 Rated short-circuit making capacity (I
cm
)
The rated short-circuit making capacity (current, voltage) is the short-circuit current that a manual motor starter can
make at a rated operational voltage, rated frequency and a fixed power factor. It is expressed as the maximum pro-
spective peak current.
2.2.3 Rated short-circuit breaking capacity
The rated short-circuit breaking capacity (current, voltage) is the short-circuit current that a manual motor starter
can break at rated operational voltage, rated frequency and a fixed power factor. It is expressed as the maximum
prospective peak current. It is expressed as the rated ultimate short-circuit breaking capacity or rated service short-
circuit breaking capacity.
2.2.3.1 Rated ultimate short-circuit breaking capacity (I
cu
) acc. to IEC / EN
60947-2
This is the maximum short-circuit breaking capacity (current, voltage) that manual motor starter can interrupt with-
out being damaged. After the short-circuit interruption, in the event of an overload, the manual motor starter is able
to trip with increased tolerances.
2.2.3.2 Rated service short-circuit breaking capacity (I
cs
) acc. to IEC / EN
60947-2
This is the short-circuit breaking capacity (current, voltage) that manual motor starters can repeatedly interrupt
without being damaged. After the short-circuit interruption, the manual motor starter is able to carry the rated oper-
ational current and to trip in the case of an overload.
2.2.3.3 What are the difference between the rated ultimate short-circuit breaking capacity (I
cu
) and rated service
short-circuit breaking capacity (I
cs
)
The difference between rated ultimate short-circuit breaking capacity I
cu
and rated service short-circuit breaking ca-
pacity I
cs
is the test sequence in IEC / EN 60947-2:
−
Part 8.3.4 Test sequence II: Rated service short-circuit breaking capacity
−
Part 8.3.5 Test sequence III: Rated ultimate short-circuit breaking capacity
The test sequence for I
cu
is O-t-CO. In this sequence manual motor starter has to switch off a short-circuit (“O”), re-
main off for 3 minutes (“t”) and then it is switched again on this short-circuit in order to switch it off (“CO”). In this
case the overload characteristic curve can change for a longer period of time and the manual motor starter does not
have the full current-carrying capacity.
The test sequence for I
CS
is O-t-CO-t-CO. In this sequence the manual motor starter hast to switch off the short-cir-
cuit (“O”), have a 3-minute break (“t”), switch on the existing short-circuit and switch it off again (“CO”), have another
3-minute break (“t”), switch on the existing short-circuit again and switch it off again (“CO”). After that, the manual
motor starter must be able to carry the full current and the overload characteristic curve must not change perma-
nently.
2.2.4 Rated short-time withstand current (I
cw
)
The rated short-time current an item of equipment can withstand is the value of the short-time withstand current,
which the equipment can carry without damage under the test conditions specified in the relevant product standard.