Sveba-Dahlen PtFL

What does Sveba-Dahlen PtFL mean?

The SD-180's Schneider frequency converter has detected that the PTC thermistor connected to digital input LI6 is either open-circuit or short-circuit, rather than presenting the expected resistance profile. Unlike otFL (which indicates genuine overheating), PtFL signals a wiring or sensor integrity failure — the circuit monitoring the motor's thermal protection has broken down and the converter cannot confirm safe motor temperature.

Symptoms

• Converter display shows 'PtFL' at startup or shortly after beginning operation
• Fault is present even when the motor is cold and has not been running
• Fault does not clear after a cool-down period, unlike genuine overtemperature trips
• No thermal events or physical obstruction evident at the motor
• PTC wiring shows visible damage, disconnection, or moisture contamination

Common causes

• Open circuit in the PTC thermistor itself (thermistor has failed or broken)
• Short circuit across the PTC thermistor due to moisture ingress or insulation failure
• Broken or disconnected wire in the PTC circuit between the motor and LI6 terminal
• Corroded or loose terminal connection at the converter's LI6 input
• Damaged cable sheath allowing conductors to short against the motor frame or conduit

Diagnostic steps

1. 01

   Isolate power and locate PTC wiring

   Isolate the SD-180 at the main switch. Trace the PTC thermistor wiring from the motor terminal box back to the converter's LI6 input terminal, inspecting the full cable run for visible cuts, pinches, or heat damage.

2. 02

   Disconnect PTC and measure thermistor resistance

   Disconnect the PTC leads at both the motor terminal box and the LI6 terminal. At ambient temperature, a serviceable PTC should read a low resistance value; an open-circuit reading (OL/infinite) confirms thermistor failure, while a near-zero reading at cold temperature indicates a short circuit.

3. 03

   Test cable continuity independently

   With the thermistor disconnected at both ends, use a multimeter to test each conductor of the PTC cable for continuity end-to-end, and confirm there is no short between conductors or to earth. Replace the cable if any fault is found.

4. 04

   Inspect LI6 terminal for corrosion or moisture

   At the converter, inspect the LI6 terminal block for corrosion, moisture tracks, or loose wiring. Clean with appropriate electrical contact cleaner, re-terminate securely, and verify the terminal is torqued to specification.

5. 05

   Replace faulty PTC thermistor if confirmed failed

   If the thermistor is confirmed open or short circuit, replace it with an equivalent PTC element matching the motor's thermal class. Reconnect wiring to LI6, clear the PtFL fault via the touchscreen, and perform a supervised restart to confirm the fault is resolved.

When to call a professional

Escalate to a Sveba-Dahlen-authorised service technician if the PtFL fault persists after thermistor and cable replacement, as the fault may lie in the converter's LI6 input circuit internally. Also escalate if the motor terminal box shows signs of moisture ingress, burnt wiring, or winding damage, as motor repair or replacement requires a qualified engineer.