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Pre-4100U Series Fire Panels (4100+, 4100A) – The older Simplex 4100 Series Fire panels have the ability to
detect Positive/Negative Earth Ground Faults. Unlike the 4100U Series Fire panels, their Power Supplies do not
have the option to automatically diagnose on which circuit the fault is located. There are, however, methods which
can narrow down the circuits in question.
To begin, when the Earth fault is currently active on the fire panel:
Disconnect the power & comms to the different bays – power down the panel first (sequentially, and one
at a time) until the Earth Fault clears from the system
After locating which bay of cards holds the problem, you will need to disconnect individual cards using the
same methodology.
Once the card in question is located, you will need to test the circuits but keep in mind the fault may be
with the card, but is more likely is out in the field.
The motherboard that the card plugs into can be the source of the Earth Fault – the protection devices on
the motherboard can fail after repeated discharges through them.
When the earth fault is located on a Mapnet or IDNet loop, disconnect one end of the loop from the Loop
card (both + and - terminals), and break the loop in different areas (i.e. line isolators for example) until the
Earth Fault disappears.
NOTE – It is possible for Earth Ground Faults to switch from Positive to Negative Earth Ground Faults (or Vice-
Versa), so when disconnecting circuits it is highly recommended that you remove BOTH the positive and negative
connections for efficient diagnosis.
If you find that all the bays have been checked, and the earth fault appears to be in the main CPU Bay, the Earth
fault will most likely be on the Auxiliary Fuse Distribution Board. The Auxiliary fuse card should be unmounted
(remove 4 screws) & insulate the Fuse Card from the mounting studs with paper or cloth. If the Earth fault
disappears, then the fault lies in the fuse card, otherwise you will need to individually disconnect each of the 24V
power supplies from the Fuse Distribution Board in turn, narrowing the circuit with the Earth Fault. If the Earth
Fault still remains, the fault is in the PSU
PLEASE NOTE – Intermittent Earth Faults can only be diagnosed whilst the fault is active.
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