Schneider LF505-S/sp26 Current Transformer Board – Tested ATV600 Sensor

What Is the LF505-S/sp26 Current Transformer Board?

The Schneider LF505-S/sp26 is the current transformer / sensor board used in high-power Altivar ATV610, ATV630, and ATV930 drives, covering the 220–315 kW range. The board’s core sensing element is the LEM LF505-S/SP26 closed-loop Hall-effect current transducer, rated for 500 A nominal with a measurement range of ±800 A. Its function is to provide galvanically isolated, accurate current feedback to the drive’s control board, enabling closed-loop motor control, overcurrent protection, and earth-fault detection.

This is a current measurement and feedback component, not the main control board or the power stage itself. Supplied as a tested replacement unit, it is intended for cases where the current sensing path has been isolated as the fault source after systematic diagnostics.

Technical Specifications

Important Diagnostic Boundary: The LF505-S/sp26 board is not the only possible cause of InF9 or InFC. Schneider’s official guidance for these faults lists bad current sensors, bad control/power board, or a poor ribbon cable connection between them as probable causes. For InFC specifically, the recommended isolation procedure is to disconnect the current transformer of the identified brick and power up; if the fault clears, the sensor is implicated; if it persists, the inverter/AFE power board should be suspected. Replacing the sensor board is appropriate only after this isolation has been performed or strongly indicated.

When to Investigate or Replace the LF505-S/sp26 Board

The board becomes the primary suspect under these conditions:

• InF9 (Internal Error 9 — Current Measurement) — the drive reports that current measurements are incorrect. This can manifest as erratic current readings, false overcurrent trips, or loss of closed-loop control stability.
• InFC (Internal Error 12 — Current Sensor Supply) — the current sensor supply monitoring has detected a low voltage level. This points specifically to the sensor supply path, which includes the transducer board.
• InF9/InFC cleared by disconnecting the sensor — if the fault disappears when the current transformer is disconnected (per Schneider’s isolation procedure), the sensor board is confirmed as the faulty brick.
• Visible damage or abnormal sensor output — physical damage on the board, or measured sensor output that does not track commanded current.

Critical caution: Before replacing this board, check the ribbon cable between the control board and power board, and rule out a control board or power board fault as the source of InF9/InFC. A new sensor board will not resolve the fault if the root cause is an unstable supply or a faulty control board.

Compatibility & Verification

Before ordering, confirm the following:

• Drive model and power rating — confirm the exact ATV610/630/930 MLFB on the nameplate. The 220–315 kW range spans specific power bricks, and the current transformer board is brick-dependent.
• Original board marking — confirm the existing board carries the LF505-S/sp26 designation, and check whether the LEM sensor marking LF505-S/SP26 is visible on the core component.
• Fault isolation — confirm whether InF9/InFC has been isolated to the sensor by disconnection, or whether the control/power board remains a possible cause.
• If uncertain, send a photo of the drive nameplate and the original sensor board label for review before purchase.

Frequently Asked Questions

Is LF505-S/sp26 a Schneider-manufactured board or a LEM sensor?

The core sensing element is a LEM LF505-S/SP26 closed-loop Hall-effect transducer. The board itself is used within Schneider ATV610/630/930 drives. The LEM designation identifies the sensor component; the “sp26” suffix refers to the specific LEM variant.

Does InF9 always mean the current transformer board is faulty?

No. InF9 indicates that current measurements are incorrect. Schneider lists bad current sensors, bad control/power board, and ribbon cable issues as probable causes. The sensor board should be replaced only after the control/power board and wiring have been ruled out.

What is the difference between InF9 and InFC?

InF9 is a current measurement error — the drive sees incorrect current values. InFC is a current sensor supply error — the drive detects that the supply voltage to the current sensors is too low. InFC points more specifically toward the sensor supply path, but can also originate from the power board