GE Mark VIeS System Manual page 377

10.6.3.1 Grounding
The Mark VIeS control system divides grounding into protective earth (PE) and functional earth (FE). The PE ground must be
connected to an appropriate earth connection in accordance with all local standards. The minimum grounding must be capable
of carrying 60 A for 60 seconds with no more than a 10 volt drop. The FE grounding must be bonded to the PE grounding at
one point or connected to an independent functional earth grounding system according to local regulations.
The JPDG board is grounded through the sheet metal bracket to the underlying back base. In most cases, this is FE grounding.
The FE ground is used as a local reference point when creating the feedback signals appearing on P2. The use of functional
earth as a ground reference does not affect the accuracy of the ac voltage detection on JAC1.
10.6.3.2 Physical Arrangement
The cabinet location of the JPDG is not critical. Connector P2 receives feedback from other power distribution boards and
passes the signals to the PPDA. The JPDG is vertically mounted, and the PPDA I/O pack is connected to the right side of the
JPDG. All the indicator lights on PPDA I/O pack are easily visible.
10.6.3.3 Ground Fault Detection
The JPDG board supports the use of a wetting voltage dc bus that is centered on ground potential by a high resistance. This
arrangement allows the detection of a ground fault when the positive bus or negative bus voltage goes to ground potential. In
support of this arrangement, the JPDG includes separate voltage feedback sensing for positive and negative power with
respect to ground. When the feedback is provided by a PPDA I/O pack, detection of ground faults is provided to the control
system.
The resistance used to center the dc bus on ground sets the ground detection sensitivity and the flow of ground fault currents.
The JPDG contains centering resistors selected by jumper JP1. If centering resistance is provided elsewhere, this jumper
should be open. The JPDG is designed to insert minimal centering resistance in the system. If JPDG is providing the centering
function, JP1 should be closed. If a JPDE is also used for distribution of the same wetting power along with a JPDG, only one
of the two should have a closed JP1 jumper.
PDM Power Distribution Modules GEH-6855_Vol_II System Guide 377
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