F10
Earth Fault Indicator
© Nortech Management Ltd, United Kingdom
2 Operation
2.1 Local Indication
On detection of fault current above the earth fault sensitivity threshold and for
the minimum required duration the F10 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 F10 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.
Manual
The F10 may be reset early, at any time during the indication period, by
pressing the RESET button on the front of the F10. Once the button is
released the F10 will be reset to the ready state.
Electrical
The F10 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.
2.4 Current Transformers
The CT combination to be used is a factory option – check with Nortech for
suitable part numbers. The F10 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 F10 is designed to operate at 45 Amps primary current. Exact operating
sensitivity can be affected by the model of CT used and fault characteristic.
The F10 requires the fault to be present for a minimum of 50ms, the operating
curve can be assumed to be close to definite time.
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