150-432-100-02, Revision 02
Appendix B - Functional Operation
HLU-432 List 1
July 18, 2002
59
G
ROUND
F
AULT
D
ETECT
The HLU-432 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 (-135 Vdc) applications, such a 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 Vdc and -135 Vdc). The circuit is constantly active during high (±112 Vdc)
applications.
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.
Whenever 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.
