F20
Twin Earth Fault Indicator
© Nortech Management Ltd, United Kingdom
Page 5 of 16
2
Operation
2.1
Local Indication
On detection of fault current above the earth fault sensitivity threshold and for
the minimum required duration the F20 will operate as follows: -
1
Flashing LED with an interval of 1.5 seconds for the duration of the
indicating period.
2
Volt free contacts operate during the indicating period.
2.2
Indication Period
The default value is 3 hours flashing when a fault is detected.
Different indication periods may be selected to suit local requirements either
at time of order or in the field using a laptop and the F20 Field Support Kit.
2.3
Reset
Automatic
The indicator returns to the ready state (LED not flashing, volt-free contacts
reset, ready to detect fault current) after the indication period has elapsed.
Each Earth fault element has its own reset timer.
Manual
The F20 may be reset early, at any time during the indication period, by
pressing the RESET button on the front of the F20. Once the button is
released the F20 will be reset to the ready state. Each Earth fault element
has its own reset button.
Electrical
The F20 may be reset early, at any time during the indication period, by either
a DC pulse (from a telecontrol RTU) or on restoration of a local AC supply.
Electrical reset signals reset both EF elements.
2.4
Current Transformers
The CT combinations to be used is a factory option
–
check with Nortech for
suitable part numbers. The F20 is designed for use with either:
Core Balanced CT
One 60/1 core balance CT having a minimum rating of 1.5VA and an accuracy
of 10% up to 4 times primary current (10P4).
Switchgear Phase CTs
Three single phase CT (typically 500:1) supplied with the Ring Main Unit.
These CT arrangements should be tested by Nortech to confirm suitability
prior to use.
2.5
Sensitivity
The F20 is designed to operate at 45 Amps primary current. Exact operating
sensitivity can be affected by the model of CT used and fault characteristic.
