12
Installation and maintenance - Three-phase induction motors
4850 en - 2018.11 / f
ASSEMBLY
It must be emphasized that these sensors cannot be used to carry out direct adjustments to the motor operating cycles.
Type
Operating
principle
Operating
curve
Breaking
capacity (A)
Protection provided
Mounting
Number required*
Normally closed
thermostat
PTO
bimetallic strip,
indirectly heated
operates on opening (0)
I
O
NRT
T
I
F
NRT
T
R
NRT
T
V
T
R
T
1.6 at 250 V
with cos
ϕ
0.6
general surveillance
for non-transient
overloads
Mounted on control
circuit
2 or 3 in series
Normally open
thermostat
PTF
bimetallic strip,
indirectly heated,
contact on closing (F)
1.6 at 250 V
with cos
ϕ
0.6
general surveillance
for non-transient
overloads
Mounted on control
circuit
2 or 3 in parallel
Positive temperature
coefficient thermistor
PTC
Variable non-linear
resistor, indirectly
heated
0
general surveillance
for transient
overloads
Mounted with associated
relay on control circuit
3 in series
Thermocouples
T
(T<150°C)
Constantan copper
K
(T<1000°C)
Copper Copper-Nickel
Peltier effect
0
continuous
surveillance
at hot spots
at regular intervals
Mounted on control
panels with associated
reading device
(or recording device)
1 per hot spot
Platinum resistance
thermometer
PT 100
Variable linear
resistance,
indirectly heated
0
high accuracy
continuous
surveillance
at key hot spots
Mounted on control
panels with associated
reading device
(or recording device)
1 per hot spot
- NRT: nominal running temperature.
- The NRTs are chosen according to the position of the sensor in the motor and the temperature rise class.
* The number of devices affects the protection of the windings.
Alarm and early warning
All protective equipment can be backed up by another type of
protection (with different NRTs): The first device will then act as
an early warning (light or sound signals given without shutting
down the power circuits), and the second device will be the
alarm (shutting down the power circuits).
Warning: Depending on the type of protection,
the motor may remain powered-up. Ensure that
the mains supply is disconnected before any work is
carried out in the terminal box or in the cabinet.
Protection against condensation: space heaters
Identification: 1 red label
A glass fibre flexible resistor is fixed on 1 or 2 coil end turns.
This resistor heats the machines when stopped and thus
prevents condensation inside the machines.
Power supply: 230V single-phase unless otherwise specified
by the customer.
If the drain plugs at the bottom of the motor have not been
removed at the time of installation, they must be opened
approximately every 6 months.
Warning: Check that the space heaters are
powered down before any work is carried out in
the terminal box or in the cabinet.
