Motor Protection; Gearboxor Shaft Seal Housingprotection; Overload Relays - Grundfos SMD Installation And Operating Instructions Manual

6.3 Motor protection

Mixers and flowmakers are provided with the
following types of motor protection:
• Standard mixers incorporate three bimetallic PTO
thermal switches. See fig. Three thermal switches.
• Standard flowmakers incorporate three PTC
sensors according to DIN 44081/44082. See fig.
Three PTC sensors.
Function of PTO 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 opens the circuit and stops the motor.
When the windings are cooled to normal temperature,
the switch closes the circuit and the motor can be
restarted manually.
See fig. Three thermal switches, section Wiring
diagrams for SMG and SFG.
Thermal switches (F6):
• two conductors, terminals 11 and 12
• maximum operating voltage: 250 V
• maximum switching current: 2.5 A at cos φ = 1
• cut-out temperature: 150 °C.
Function of PTC sensors
When overheated, the motor stops. Automatic
restarting is not permitted. This requires a thermistor
trigger unit with a reconnection suppressor in the
control circuit of the motor contactor.
See wiring diagram in fig. Three PTC sensors,
section Wiring diagrams for SMG and SFG.
ϑ1, ϑ2, ϑ3: 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 cut-out temperature (130 °C) R ≥ 4000 Ω.
The voltage at terminals 31 and 32 must
not exceed 2.5 V (AC/DC). Considered
this when conducting tests with an ohm-
meter.
Explosion-proof SMD mixers must be pro-
tected against too high temperature by
PTC or PTO (Klixon) sensors. The sensors
must be connected to a certified signal
converter with the safety level, SIL 1. If the
relay is built in as part of a frequency con-
verter, the converter must also fulfil SIL 1.
6.4 Gearbox or shaft seal
housing protection
The gearbox or shaft seal housing is monitored for
leakage by an incorporated leakage sensor.
The leakage sensor must be connected to a Grundfos
ALR-20/A-Ex relay
The ALR-20/A-Ex relay must be ordered separately.
Part number: 99794613 or 96489569.
If the gearbox or shaft seal housing is not monitored
for leakage, inspect it every 6 months. If the oil
contains water, replace the shaft seal.
For details on SMD cable Ex, see the SE cable
Ex Installation and operating instructions

6.5 Overload relays

Adjust the relay to the rated current stated on the
nameplate.
= 2.5 V
max.
Incorporate electro-thermal all-pole triggers in all six
mains conductors (U1, V1, W1 and U2, V2, W2).
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Connect the pumps to a controller with a
motor protection relay with IEC trip class
10 or 15 or NEMA-equivalent.
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