Item no. 789-665

Ground resistance signaling module; Ground fault alarm via digital output; Supply voltage: 24 VDC; Module width: 18 mm

Item no. 789-665
Ground resistance signaling module
Short description:
WAGO's module signals a value falling below a non-adjustable, asymmetric isolation resistance between +24 V or 0 V of the supply voltage and ground with a potential-free (Iso OK) contact and status LED. The Iso OK contact can be evaluated via a PLC.
This status is maintained until the next measurement interval.
Operation with Grounded Control Circuit (Functional Potential Equalization)
  • The module establishes an internal connection between the 0 V (X2.2) and ground (X2.1) connections via a semiconductor switch.
  • At 10 s intervals, this connection between 0 V and ground is interrupted for 0.5 s, and the isolation resistance between +24 V (X1.3) or 0 V (X2.2) of the supply voltage and earth (X2.1) is determined.
  • The grounding connection on the module does not meet the requirements of a protective earth terminal (PE). It serves as a functional ground. The measurement method does not involve the module establishing any permanent connection between 0 V and ground.

Operation with Ungrounded Control Circuit
  • In this operating mode, the semiconductor switch to establish a connection between 0 V (X2.2) and ground (X2.1) is deactivated. At 1 s intervals, the isolation resistance offset is determined for 0.5 s.
  • The module does not meet the requirements of an isolation monitoring device per EN 61557-8.

“Iso OK” Contact
  • The potential-free contact serves the purpose of supporting evaluation (e.g., via a PLC) of looming isolation faults.
  • This contact must not be used to switch safety-related products that could cause the circuit to switch off.