
Premise/Theory
The control panel internally causes its power negative to float 1 volt below earth ground as shown in the first
diagram below. If any wire attached to the panel shorts to earth ground or a voltage source, it will become the same
reference level as earth ground, causing the panel to see a ground fault.
Normal
operation
1VDC measured
from KP(-) to earth
shorted to
ground.
0VDC measured
from KP(-) to earth
Panel not happy
shorted to
ground.
13VDC measured
from KP(-) to earth
Panel not happy
shorted to ground.
6 VDC measured
from KP(-) to earth
Panel not happy
proper earth ground, it
is unable to sense a short
to earth ground.
1 VDC measured
from KP(-) to earth
Panel is happy
(Despite the real ground fault!)
Terminal 30 not
connected to a
proper ground
Table 3: Ground Fault Voltages
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