
MANUAL MOTOR STARTER GUIDE
APRIL 19
20/80
2.2.8 Trip-free mechanism
As required by IEC 60947-1, the manual motor starter features a trip-free mechanism. This means that the manual
motor starter trips even if the handle is locked in the “ON” position or held by hand. According to IEC 60204, a supply
disconnecting device also requires a trip-free mechanism.
2.2.9 Phase loss sensitivity
According to IEC 609471-4-1, phase loss sensitivity is a characteristic of an inverse time-delay thermal over-current
release. In the case of a loss of incoming power or a strong imbalance of the phases, this ensures that the manual
motor starter trips.
Timely tripping in the event that a two-phase supply is too long prevents an over current in the remaining phases,
which could damage the motor or other loads.
Limits of operation
No tripping within 2 hours
2 Pole: 1.0 x I
e
1 Pole: 0.9 x I
e
Tripping within 2 hours
2 Pole: 1.15 x I
e
1 Pole: 0 x I
e
Table 6: The information above is based IEC 60947-4-1
During normal operation, the device should be symmetrically loaded on all three poles to prevent early tripping due
to phase loss sensitivity. In order to protect single-phase or direct-current devices, all three main poles have to be
connected in series, see also Chapter: 2.1.7 Single-phase and direct current (DC) loads.
2.2.10 Mechanical and electrical durability
Due to product design characteristics, manual motor starters vary in regard to the number of electrical and mechani-
cal operations which can be sustained over the product life. Below is a comparison between manual motor starters,
contactors and circuit-breakers.
Rating
Manual motor
starters
Contactors
< 100 Amps
Circuit-breakers
Mechanical durability
Up to 100,000
>10,000,000
25,000
Electrical durability
Up to 100,000
>1,000,000
8,000
Table 7: Examples of mechanical and electrical durability
Since molded case circuit-breakers are designed to protect circuits and loads rather than control them, the mechani-
cal and electrical durability of these devices is quite low. Contactors which are designed specifically for load control
have very high mechanical and electrical durability. Manual motor starters which are designed to provide both con-
trol and protection are rated higher than general circuit-breaker types.