Fault Thrower

Part of our Horizon family of products, the Fault Thrower provides a means of deliberately introducing a phase to earth fault in order to ensure remote end tripping of a circuit breaker, assuming pilot wires are not available for inter-tripping.

The need to operate the remote circuit breaker can be due to equipment faults, such as thermal protection or low level fault currents that cannot be detected by the remote protection.

A typical application is with transformer feeders to enable the remote feeder breaker to respond to the transformer local fault detecting relays, such as Buchholz protection,  local earth fault protection etc.

Key Features

  • Superior, proven technology using a single phase vacuum interrupter driven by a magnetic actuator for fault initiation
  • The switch is housed in an aluminium tank, dielectric insulation is provided by SF6 gas
  • Connection to the system is achieved by either a separable connector or open terminal bushing
  • Manual release of the switch is available within the control cubicle housed under the tank
  • The fault is ‘thrown’ through the aluminium tank, two earth points are provided for safely earthing the equipment steel work and to provide a fault path


Rated Voltage kV 38
Short Circuit Making Current kA 25
Impulse Voltage Withstand kV 170
Power Frequency Withstand (Wet & Dry) kV 80
Control Voltage V dc 110 (48 & 220 optional)
Rated Frequency Hz 50 / 60
Rated 3 sec Short-Time Current kA 25
Peak Short Circuit Making Current kA 63
Peak Withstand Current kA 63
Internal Arc (EATS 41-36) kA for 1s 31.5
Fault Making Time 190ms
Endurance at 25kA 50 makes
Temperature Range ˚C -50 to +50
Weight kg 500