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Dimensions
Section 12
11
Choice of motor supply cable size
When selecting the cable size the starting current of the motor and the permissible
voltage drop must be taken into account. The cable must be capable of carrying a
permanent service current at least equal to the sum of In + Is/3 where:
In = rated current
Is = starting current (4 - 8 In) depending on the motor.
Voltage drop
The permissible voltage drop from the start of the installation to the motor in
question is 6% for public distribution systems. If the torque of the machine to be
driven is low during starting it is only necessary to check the voltage drop for the
rated current of the motor. If the starting torque is high (grinding mills, goods lifts,
etc.) the voltage drop should be checked for the starting current.
P25M motor circuit breaker
This protects motors against overloads and short circuits. P25M type circuit breaker
has on each pole a thermal release for protection against overloads and a magnetic
release for protection against short circuits. For high short circuit currents use the
limiter block, Ref. 21115. For ratings from 0.16A - 10A. 415V or from 0.16 - 18A,
240V; in this case the breaking capacity of the P25M circuit breaker is unlimited.
Applications
The P25M circuit breaker is particularly suitable for protecting
small machine tools
and similar machines, with
local control.
Thermal release settings
The thermal releases are supplied set to the bottom value of the setting range.
Simultaneous setting of the thermal releases can be carried out by opening the cover
and adjusting the dial on the front face of the P25M. It is recommended that the
thermal releases be set to the current that the motor absorbs in normal service and
not to its rated current so as to provide effective close protection.
Ambient temperature compensation
Close protection against thermal overload is enhanced by thermal releases which are
ambient temperature compensated over the range - 20°C - +60°C. During overload
conditions, tripping is delayed at lower ambient temperatures, from - 20°C - +20°C,
and is accelerated at higher ambient temperatures, from 20°C - +60°C.
Protection of the line supplying the motor
Every circuit and every motor must be protected against overloads and short
circuits.
Phase failure protection
The P25M protects each phase separately and interrupts all three phases in the
event of a loss of phase. Single phasing sensitivity is achieved by means of a
differential trip which accelerates tripping should phase failure occur.
P25M circuit breakers
Motor
protection