F20
Twin Earth Fault Indicator
© Nortech Management Ltd, United Kingdom
Page 9 of 16
4
Installation
4.1
Physical
The F20 has an outer polycarbonate enclosure. The electronics are
encapsulated in the lid. The LED and buttons are located on the front of the
F20.
The F20 should be mounted for good visibility and as close as practical to the
CT.
4.2
CT earthing
For safety reasons, it is normal practice for the CT to be mounted in a
position over the cable sheath or screening tape, and in accordance
with local safety regulations.
When an earth fault occurs in a cable network the majority of return current
will flow through the cable sheath, thus resulting in a null output from the
core balance CT, as shown in the figure below.
INCORRECT Earthing
Incorrect Earthing
This effect can be prevented if the cable earthing connection between the
cable and adjacent switch is routed through the core balance CT shown below.
Correct Earthing
Correct Earthing
Where single core cables are used, each sheath earth-wire must be routed
through the single core balance CT.
