Neutral Earth Resistor Monitor

SE-330AU Series

Added to List
  • Compliant with Australian standards 
  • Additional features with new revision
  • Detects resistor failure with or without an earth fault present


The Littelfuse SE-330AU is an advanced earth fault and neutral earthing resistor monitoring relay for low and medium-voltage transformers and generators. It monitors neutral current, neutral-to-earth voltage, and neutral-to-earth resistance. 

The SE-330AU earth fault function complies with AS/NZS 2081.3:2002.

One of the leading types of neutral earthing products, the relay provides continuous monitoring of the neutral-to-earth path to verify that the neutral-earthing resistor (NER) is intact. This is of utmost importance – an open NER renders current-sensing earth fault protection inoperative and could result in a false belief that the system is functioning properly.

We are the exclusive NSW supplier of Littelfuse protection relays and controls for the protection, safe control and distribution of electrical power in industrial applications.

Resistor Monitoring

Combines the measured values of resistance, current, and voltage to continuously determine that the NER is intact. It is able to detect a resistor failure with or without an earth fault present. Sensing resistors are matched to the system voltage and are used to monitor NGRs on systems up to 35 kV.

Earth Fault Monitoring

Uses a 5- or 30-A-primary current transformer to provide a pickup-setting range of 0.125 to 5 A or 0.75 to 30 A to comply with AS/NZS 2081.3:2002. DFT filtering ensures that false trips due to harmonic noise from adjustable-speed drives do not occur. Open-CT detection is provided.

New revision additional features

100 trip records with date and time stamp - A mini-USB interface to view measured values, configure settings and check event records using SE-MON330 v3.2 or later - An on-board microSD card (included) can be used for long term data logging and firmware upgrades - Earth fault trip level is adjustable from 0.125 to 5A (EFCT) or 0.75 to 30A (CS30). When set to MEM, the earth fault trip level is adjustable from 2 to 100% in 1% increments of the CT-primary rating. SE-MON330 V3.2 or later is required. - Dual Ethernet ports are optionally available with support for fiber and RJ45 interfaces - IEC 61850 protocol is optionally available

Computer to relay connection

Connect the SE-330AU to the network using a standard Ethernet patch cable. Use of a crossover cable to connect the SE-330AU directly to the computer running IP-Config is not recommended. A typical router will assign an IP address to all connected computers that are using DHCP. The SE-330AU does not support the use of DHCP. If the SE-330AU is being set-up for first time, it is recommended to only have one SE-330AU connected to the network to prevent communication errors.

Datasheets and Manuals

Changes to SE-330SE-330 Datasheet (updated version)SE-330 Manual (updated version)SE-330 Manual (previous version)SE-330 DeviceNet Electronic Datasheet EDS (new version)SE-330 DeviceNet Electronic Datasheet EDS (previous version)SE-330 EthernetIP electronic Datasheet (new version)SE-330 EthernetIP electronic Datasheet (previous version)SE-330 DeviceNet Manual (previous version) SE-330 EthernetIP Manual (previous version) SE-330 Profibus Manual (previous version)

Software and Manuals

SE-MON330 v4.0 Software SE-MON330 v4.0 Software Manual

CAD Drawings and Models

ER-15Kv 3D ModelER-25kv CAD DrawingER-600VC CAD Drawing

GF Trip-Level Settings

0.125 to 30 A

GF Trip-Time Settings

0.1 to 0.5 s

Vn Trip-Level Settings:

20-2,000 Vac (≤5 kV systems) 100-10,000 Vac (>5 kV systems)

Output Contact

Two Form A, Two Form C

Operating Mode


Harmonic Filtering

Standard feature


Front panel push button and remote input




Mini USB (standard); DeviceNet (optional), IEC 61850 (optional), Modbus TCP and EtherNet/IP (optional)

Analog Output

4-20 mA, self or loop powered


H 213 mm, W 98 mm, D 132 mm

Conformal Coating

Standard feature


5 years

Mounting Panel Surface (optional)

Makes Perfect Sense

Exceptional choice, exclusive ranges, high stock levels, excellent value and a passion for expert personal service. Why would you look anywhere else for your electrical, lighting, air conditioning and refrigeration needs?