System Power Connection - GE Mark VIe System Manual

6.8 System Power Connection

Control cabinets are shipped with complete internal cabling. Power cables from the power distribution module to the control
modules, interface modules, and terminal boards are secured by plastic cable cleats located behind the riser brackets. The
mounting brackets and plates cover most of this cabling.
6.8.1 I/O Wiring
I/O connections are made to terminal blocks on the control system terminal boards. Shielding connections to the shield bar
located to the left of the terminal board are displayed in the following figure.
I/O Wiring Shielding Connections to Ground Bar at Terminal Board
The grounded shield bars provide an equipotential ground plane to which all cable shield drain wires should be connected,
with as short a pigtail as practical. The length should not exceed 5 cm (2 in) to reduce the high-frequency impedance of the
shield ground. Reducing the length of the pigtail should take precedence over reducing the length of exposed wire within the
cabinet. Pigtails should not be connected except at the grounding bars provided, to avoid loops and maintain a radial
grounding system. Shields should be insulated up to the pigtail. In most instances, shields should not be connected at the far
end of the cable, to avoid circulating power-frequency currents induced by pickup.
A small capacitor can be used to ground the far end of the shield, producing a hybrid ground system, improving noise
immunity. Shields must continue across junction boxes between the control and the turbine, and should match up with the
signal they are shielding. Avoid hard grounding the shield at the junction boxes, but small capacitors to ground at junction
boxes may improve immunity.
152 GEH-6721_Vol_I_BP GEH-6721_Vol_I Mark VIe and Mark VIeS Control Systems Volume I
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