The DGF7-18 is a microprocessor based ground fault unit for use on solidly grounded or resistance
grounded systems. This innovative digital electronic unit measures ground fault current using a built-in 28
mm zero sequence Current Sensor (CS), or an external CS. External CSs with different cable windows,
round or square and split core, and various current ratios are available.
The system will react to alternating current (AC) only and will reject direct current (DC) signals. Accuracy
will be maintained over a frequency range of 45 - 400 Hz, making it suitable for variable frequency drive
applications. The DGF7-18 is a Class A device as defined in the IEC 60755 standard; it is therefore fully
characterized for operation with sinusoidal AC and pulsating DC currents.
The maximum system operating voltage for the DGF7-18 is 660 V when passing the system power
conductors through the built-in CS. However, by using any GFS external CS and insulating the busbars, or
by using any suitably rated, commercially available, interposing CT and passing the secondary lead
through the built-in CS, the unit can be used on any system voltage.
The DGF7-18 houses a non-isolated universal power supply from 24 - 240 V AC or DC and is equipped
with form ‘Z’ (4-wire) isolated N.O. and N.C. contacts to operate the upstream protection device and to
indicate a failure of the system. The unit will operate in one of two modes: Non-Failsafe or Pulsed Trip/
The Ground Fault Current Trip level (30 mA – 6 A, 8 steps) and Trip Delay Time (20 ms (instantaneous),
500 ms) are set on a front accessible dipswitch array.
By double clicking the remote ‘RESET’ button a functional test of the DGF7-18 is invoked. A single press
of a N.O. remote ‘RESET’ button resets the unit after a trip. It is not necessary to press a N.C. remote
‘RESET’ to invoke Auto Reset.
A green LED indicates three functions: slow flashing denotes Control Voltage is present; steady on after a
test was invoked; fast blinking denotes the unit has sensed a ground fault current higher than the Trip
Level for a period longer than the Trip Delay Time and that the output contacts have operated.
A 10 point Pull-apart terminal block simplifies connection of field wiring.
To insure that the DGF7-18 will function in severe circumstances, it is encapsulated in polyurethane
(PUR) to make sure it is not vulnerable to mechanical shock, vibration nor weather.