Opto F+E 3.0

Short-circuit and earth fault indication with fibre optic cables for transferring signals

The Opto F+E 3.0 device is a combined short-circuit and earth fault indicator. It is designed to detect, display and remotely indicate short-circuit currents and earth faults in medium voltage distribution networks. The indicator unit can be used in all medium voltage switchgear installations.

Fibre optic cables provide electrical isolation between the current transformers, mounted on cable/busbar, and the display unit when transferring signals. Due to its measuring principle, the earth fault indication is suitable for low-impedance or solidly earthed neutral networks as well as for radial or open ring networks.

The current transformers (CT) have an integrated trip threshold detection capability. When the pre-set trip current is reached or exceeded, light pulses will be emitted. A fibre optic cable is used to transmit these light pulses from the CT to the Opto. Phase-selectively operated red LEDs start flashing.

After the first tripping incident (e. g. in radial systems) the LEDs begin a phase-selective flash rhythm of: flash / pause / flash.

A second tripping (e. g. ring operated network with auto-reclosing) is indicated by flashing LEDs of the fault-affected phases in a flash-flash / pause / flash-flash rhythm.

Equipment set includes:

  • 1 display unit (plug-in or surface mount housing)
  • 3 phase current transformers
  • 1 summation current sensor
  • 4 fibre optic cables
  • Fibre optic cables for electrical isolation between indicator and current transformers
  • „„High-intensity LED indication
  • „„Single and double flash mode for operation in radial and ring networks
  • „„Remote indication via relay contact
  • „„Current transformer retrofit ready

Your advantages

  • Installation on bare cables and busbars
  • „„New fault detection within reset time

Technical specifications

Earth fault detection methods

Earth short-circuit

Low-impedance/short-term low-impedance earthed ---
Isolated earthed -
Resonant earthed -
Short-circuit trip current

400, 600, 800 or 1,000 A

Response delay short-circuit

40, 60, 80, 100, 200, 300 or 500 ms

Earth short-circuit trip current

10, 20, 40 or 80 A resp.

40, 80, 120 or 160 A

Response delay earth short-circuit

60, 100, 200 ms

Trip current transient method -
Trip current active current cos ɸ -
Response delay active current cos ɸ -
Trip current reactive current sin ɸ -
Response delay reactive current sin ɸ -
Trip current permanent earth fault -
Response delay permanent earth fault -
Trip current pulse detection -

Short-circuit: 3 red LEDs (L1, L2, L3), earth fault: 1 yellow LED, flashing period 2 s, double flash sequence 0.3 s with flashing period 3 s

Relay contacts 2
Remote contact

Potential-free permanent or momentary contact

Contact capacity: 380 V AC/5 A/1250 VA max.

220 V DC/5 A/150 W max.

RS485/Modbus-RTU -
USB port -
Binary inputs -
Manual reset ---
Remote reset ---
Automatic time reset ---
Reset via interface -
Reset on current restoration -
Reset on voltage restoration ---
Reset on restoration of auxiliary supply ---
Reset via Explorer Software -
Internal power supply

Long-life lithium cell, active flashing time >1,000 h, shelf life ≥20 years

External auxiliary supply 12 – 110 V DC ±10 % or 24 – 60 V AC (±10 %), 50 – 60 Hz (optional)
CT powered -

Polycarbonate, IP40 (plug-in housing), IP65 (surface mount housing)

Temperature range -30 to +70 °C
Cable diameter -

1. Phase-selective short-circuit indication

2. Separate earth fault indicator

3. Setting options via DIP switches

4. Connection of fibre optic cables

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