Littelfuse, Inc. SE-330AU Series – Neutral-Earthing-Resistor Monitor SE-330AU-25-01

The SE-330AU is an advanced earth-fault and earthing-resistor monitoring relay designed for low- and medium-voltage transformers and generators. It continuously monitors neutral current, neutral-to-earth voltage, and neutral-to-earth resistance, ensuring the integrity of the neutral-earthing resistor (NER). This monitoring is critical, as a failure in the NER can compromise earth-fault protection. The device complies with AS/NZS 2081.3:2002 and features four relay outputs along with an analog output. It includes a mini USB port for configuration and data viewing, and an onboard micro SD card for long-term data logging. The SE-330AU can detect resistor failures with or without an earth fault present and is suitable for systems up to 35 kV. It utilizes a 5- or 30-A primary current transformer with a pickup-setting range of 0.125 to 30 A, incorporating DFT filtering to prevent false trips from harmonic noise. The product also supports various communication options, including DeviceNet and IEC 61850, and features a fail-safe operating mode. It is designed for panel or surface mounting and comes with a five-year warranty.