ATEX-certified motor thermal protection function with PTC thermistor relays (+L513+Q971) 17
Operation principle
Without an FSO module
1. When the motor temperature rises to the thermistor wake-up level, the resistance of
the thermistor increases sharply.
2. The PTC thermistor relay detects the change and indicates motor overtemperature
through its output contacts.
3. The opening contacts of the PTC relay(s) open the STO circuit of the drive. This
prevents the drive from generating the torque required to rotate the motor.
4. The drive generates an STO indication (parameter 31.22, see page 44).
5. If the auxiliary contacts of the PTC relays are wired to a digital input, the loss of the
signal triggers a motor overtemperature indication in the drive (see page 44).
6. After the motor temperature has decreased to normal, the user resets the PTC relay(s)
using remote reset buttons (or the buttons on the PTC relays themselves). See the
circuit diagrams of the delivery.
7. Optional
: The user resets the drive faults either from the reset source defined by the
user (parameter 31.11, see page 45) or locally with the drive control panel:
• the STO fault in the drive (if configured with drive parameter 31.22, see page 44)
• the motor overtemperature fault in the drive (if configured, see page 44).
WARNING! We recommend that you do not use the autoreset setting (that is,
short-circuit the reset switch terminals of the PTC relay) with a safety device
protecting an Ex motor.
00 ACS880 ATEX cabinet.book Page 17 Tuesday, May 28, 2019 10:25 AM
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