20
Electrical Connection
In the case of a high start-up frequency, intermittent operation and switching rate, and
to provide optimum protection against 2-phase running, we recommend that motors
are protected by thermal overcurrent relays/motor circuit breakers, in addition to PTC
resistors.
In the event of a shutdown after a fault check whether this is due to one of the
aforementioned causes.
Motor protection with thermal contact
Thermal contacts are temperature-dependent operation elements that automatically
monitor the winding temperature of a motor. Compared to thermal tripping devices and
motor circuit breakers, these devices provide more effective protection under the following
circumstances when installed in the motor winding:
– Insufficient cooling
– Increased ambient temperature
– Extreme speed reduction during control and regulation operations
– Shutdown of the motor in the event of control voltage failure on the line side
– Faulty contacts and cable breakages in the control circuit.
The thermal contact opens when the permissible temperature of the winding is exceeded.
This interrupts the control signal loop of a control unit, for example.
The fan protection drops out and disconnects the motor from the mains.
The motor protection is intrinsically safe.
Connecting electric motors
In order for the unit to operate properly it is important to connect it with a
righthand
rotating field.
• Check the rotating field if necessary with a rotating field meter.
DAMAGE TO THE UNIT!
Correct assignment of the phase sequence to the specified rotational direction must be
checked before the motor is connected. If the wrong connection is made the motor/fan
may be damaged.
The terminals of AC motors are labelled in such a way that the alphabetical sequence
of the terminal designation U1, V1, W1 corresponds with the temporal sequence of the
phases L1, L2, L3 (with clockwise rotation).
The rotational direction can be reversed by exchanging two connecting cables:
– Exchange the connecting cables, e.g. U1 and V1
– Y connection: Exchange the connecting cables, e.g. U1 and V1
– Δ connection: Exchange the connecting cables, e.g. U2 and V2
– Speed 1: Exchange the connecting cables, e.g. 1U and 1V
– Speed 2: Exchange the connecting cables, e.g. 2U and 2V
– Speed 3: Exchange the connecting cables, e.g. 3U and 3V
• Make sure that the supply voltage with mains frequency is between 95 % and 105 %
of the rated voltage. Only then can the motors to operate at their rated output, otherwise
they may be damaged.
To make the connection, proceed as follows:
• Connect the unit according to the wiring diagrams.
Extended motor protection
Shutdown after fault
Single-phase electric motors
with direct on-line starting:
Single-speed electric motors
with Y/Δ starting:
Multi-speed electric motors:
Voltage fluctuations
