18 Implementing a Safe disconnection function
resistance of the temperature sensor increases sharply. The relay detects the change and
indicates motor overtemperature through its output contacts. The opening contacts break
the Safe torque off circuits of the drive, thus disconnecting the power supply from the
motor.
Use an ATEX-compliant protection relay only. The example employs an ABB CM-MSS.41
thermistor motor protection relay. You can find more information on that relay on the
Internet, for example, in the data sheet of the relay (2CDC112216D0201). This relay
enables implementing the manual reset function. When you use it, no drive parameter
needs to be set to Fault.
Include the protection relay test to the start up and acceptance test of the thermal motor
protection circuit. See the relay manual for the relay tests.
Wiring
General wiring instructions
Wire only the sensor circuit into the potentially explosive atmosphere.
Install the drive/inverter module, the Safe torque off circuit, and the protective relay outside
the hazardous zone.
For the STO circuit wiring, use the type of cable specified in the appropriate hardware
manual.
Route the sensor cables away from the motor cable.
We recommend to use shielded sensor cable to minimize electromagnetic interference
from power cables.
Connect the control cable shields to the chassis only.
The installation must comply with the requirements of the relevant standard(s) of EN/IEC
60079 series.
The installation of the sensor circuit in the Ex Zone must comply with the requirements for
the applicable type of protection, such as:
• Ex d (EN/IEC 60079-1),
• Ex eb (IEC 60079-7:2015; Ex e in EN 60079-7:2007 and IEC 60079-7:2006),
• Ex ec (IEC 60079-7:2015; Ex nA in EN/IEC 60079-15:2010).
Wiring diagrams
See the appropriate section.
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