
150-231-184-05, Revision 05
Appendix B - Functional Operation
HLU-231 List 8D
October 25, 1999
57
G
ROUND
F
AULT
D
ETECT
The HLU-231 has a Ground Fault Detect (GFD) circuit which detects a ground or a resistive path to ground on
any wire of any loop of any span with a non-zero voltage. For low voltage applications (-140 V), this circuit is
active during start-up by applying the bipolar voltage to the loops. It deactivates when going to the nominal
operation mode of unipolar negative voltage (0 V and -140 V). The circuit is constantly active during high voltage
applications (±112 V).
When the circuit is active, the system is compliant with Class A2 requirements of GR-1089. When the circuit is
not active, the system is compliant with Class A3 requirements of GR-1089.
When the GFD circuit detects a grounded loop, the line power is immediately removed from the spans and a PWR
FEED GND alarm is generated and displayed. The power is reapplied 30 seconds later as part of a new start-up
procedure. If the ground condition persists on the span, the power is removed again once the GFD circuit detects
the grounded loop.
The indication of the location of the ground fault can be obtained by monitoring the voltages on the spans on the
HLU side as it sequentially powers devices in subsequent spans.