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7.1 Motor protection
The pumps are provided with the following type of motor
protection:
Standard SRP pumps incorporate three bimetallic PTO thermal
switches (PTO = Protection Thermique á Ouverture). See fig. 17.
Explosion-proof SRP pumps incorporate three PTC sensors
(temperature sensors) according to DIN 44 081. See fig. 18.
Function of thermal switches
The motor is protected against overheating by three thermal
switches connected in series, one switch in each winding.
When the maximum winding temperature is reached, the switch
will open the circuit and stop the motor.
When the windings have cooled to normal temperature, the
switch will close the circuit and the motor can be restarted.
Manual restarting is necessary.
See wiring diagram in fig. 17, section
Thermal switches (F6)
• Two conductors (terminals 11 and 12).
• Maximum operating voltage of switch: 250 V.
• Maximum switching current: 2.5 A at cos
φ
= 1.
• Cutting-out temperature: 150 °C.
Function of PTC sensors
The motor is protected against overheating by three thermal
sensors connected in series, one in each winding. When
overheated, the motor will stop. Automatic restarting is not
permitted in such cases. This requires a thermistor trigger unit
with a reconnection suppressor in the control circuit of the motor
contactor.
See wiring diagram in fig. 18, section
ϑ
1,
ϑ
2,
ϑ
3: PTC sensors:
• Two conductors (terminals 31 and 32).
• Maximum voltage at the terminals: U
max.
= 2.5 V (AC/DC).
• Resistance between terminals 31 and 32:
- at room temperature R = 150 to 750
Ω
.
- at cutting-out temperature (130 °C) R
≥
4000
Ω
.
7.2 Gearbox protection
The gearbox is monitored for the ingress of water by a leak
sensor incorporated in the gearbox.
If the monitoring function is required, the leak sensor must be
connected to a Grundfos relay, type ALR-20/A-Ex.
The ALR-20/A-Ex relay must be ordered separately.
Product number: 96489569.
For longer distance, use an additional, screened cable.
An external alarm indicator, if any, must be connected to the
potential-free outputs, terminals 1 and 3 or 4, respectively.
Maximum load: 250 V, 5 A.
When the ALR-20/A-Ex relay is connected, a current of up to
10 mA will flow through the leak sensor (terminals 21 and 22).
If water penetrates into the oil chamber, the relay will trigger an
alarm signal and/or switch off the motor.
See wiring diagram in fig. 17 or 18, section
.
Leak sensor
• Two conductors (terminals 21 and 22).
• Maximum operating voltage: Approx. 12 V.
• Maximum current: 1 to 10 mA.
To adjust the sensitivity of the ALR-20/A relay, proceed as
follows:
1. Turn adjusting screw (pos. a) on the relay until indicator light
(pos. b) illuminates.
2. Turn the adjusting screw in the opposite direction until the
indicator light goes out.
3. Continue to turn the adjusting screw 60 ° (same direction as
instep 2).
Note
For transmission tests at terminals 31 and 32, the
test voltage must not exceed 2.5 V (AC/DC).
Use an ohmmeter for the test.
Warning
Explosion-proof pumps must be protected
against too high temperature by means of PTC
sensors. The sensors must be connected to a
certified signal converter.
Warning
Explosion-proof pumps must be connected to the
Grundfos relay, type ALR-20/A Ex.
Classification: II (2)G [Ex ib] IIC
Product number: 96489569
Note
The cable between the relay and the pumps must
be maximum 50 m.
Warning
If the supply cable to the sensor is lengthened,
comply with the ATEX directive as well as the
EN 60079-0 and EN 60079-14 standards for the
intrinsically safe circuit.
The terminal connections of the intrinsically safe
and the not intrinsically safe circuits must be
separated and must be clearly distinguishable.
The operator must make sure that all installation
work is done in conformity with the relevant
standards.
