Electrical Protection; Motor Protection - Grundfos SRG Serie Instrucciones De Instalación Y Funcionamiento

4.5 Electrical protection

4.5.1 Motor protection

The pumps are provided with the following type of
motor protection:
Standard SRG pumps incorporate three bimetallic
PTO thermal switches (PTO = Protection Thermique
á Ouverture). See fig. 11.
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. 11.
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 (optional)
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. 12.
1, 2, 3: PTC sensors:
• Two conductors (terminals 31 and 32).
• Maximum voltage at the terminals: U
(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.
For transmission tests at terminals 31 and
32, the test voltage must not exceed 2.5 V
Note
(AC/DC).
Use an ohmmeter for the test.
4.5.2 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.
The ALR-20/A relay must be ordered separately.
Product number: 96489569.
Note
For a 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 5 and 7 in fig.
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.
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.
= 2.5 V
max.
3. Continue to turn the adjusting screw 60 ° (same
direction as instep 2).
The cable between the relay and the pump
must not be longer than 50 m.
13 connected to wires 21
11 or 12.
Warning
When adjusting the relay, beware of
electric voltage.
13