Design
The earth fault indicator type EFL-A consists of:
1.) reading instrument
2.) sensor
3.) connection cable
The electronics of the reading instrument are encorporated in a square housing. The electronics are fully sealed and thus they are protected against damaging or environmental influences. At the front of the reading instrument there is a screw closure, which can be opened for changing the battery. The reading instrument has the protection class IP 65, so it can be applied indoors and outdoors.
For mounting the earth fault indicator,
only two drillings with a diameter of 4 mm must be inserted. The housing must then be fixed via 2 pcs. of screws M4.
Function
The sensor is mounted around all the three conductors of the cable, in order to detect the sum current of the conductors (cores) L1, L2, L3. Normally, the sum current is about 0A. If there is an earth fault in one of
the conductors, the summary current will increase due to this asymetric situation. This increased current will be detected and transmitted to the reading instrument for evaluation. The earth fault will be indicated, if the fault current exceeds the preadjusted operating point.
In order to avoid wrong indications caused by current peaks (e.g. due to switching processes), the indicator is equipped with a setting for minimum impulse duration. All impulses from the sensor are checked. For example, the indicator is adjusted to a minimum impuse duration of 80 ms. If the incoming impulse is shorter than 80 ms, no earth fault will be indicated. If the incoming impulse is longer than 80 ms and exceeds
the operating point, an earth fault is indicated.
This minimum impulse duration can be adjusted in the range of 40 to 300 ms.
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