P28 Branch Circuit Protection; 125 V Dc Power Protection; 125 V Dc Branch Circuit Protection - GE Mark VIeS System Manual

P28 Branch Circuit Protection

Branch circuit protection, starting at the terminal board and working back toward the power source, is displayed below:
• Terminal boards supplying output power to field devices provide individual branch circuit protection using a small three
terminal regulator. The regulator includes a thermal shut down feature that responds quickly to any overload condition.
• All I/O packs have a fast acting solid-state circuit breaker at the power input point. This breaker ensures that any problem
with a connected terminal board can not propagate to other system components.
• The pack circuit breaker is used as a soft-start feature for the pack. Hot-plugging the 28 V dc power into a pack results in
a very gradual turn-on of the pack. This ensures no other system component can be affected.
• The JPDS board does not use fuses. It is rated for Class I Division 2 (potentially explosive atmosphere) and the use of
fuses is not desired. The JPDS wiring is protected by self-restarting devices rate at 1.4 A.
• Each power supply has current limiting on the output. When JPDS is used for distribution, this current limit protects
branch circuit wiring. Multiple supplies, exceeding 500 W, use JPDS with external fuses.
Distribution component design provides control power branch circuit protection. Specific areas that require monitoring are:
• Supply current limit protecting wiring cannot exceed 500 W. The maximum allowable wire size must be used in the
Mate-N-Lok connectors.
• Maximum allowable wire sizes must also include wiring to Ethernet switches and control rack power supplies.
• Parallel or single 28 V supplies, yielding a total capability greater than 500 W, must include branch circuit protection
using JPDG where the protection is included, or JPDS with added external branch circuit protection.

10.1.3.2 125 V dc Power Protection

Characteristics for using a 125 V dc battery as a power source for the PDM are as follows:
• A nominal 125 V dc battery is used as a dc power source for the PDM.
• The maximum voltage the dc battery can feed to the system is 140 V dc.
• The 125 V dc input to 28 V dc output supply, used to supply control electronics, can function down to 70 V dc. Field
devices must be reviewed on an individual basis.
Note The Mark VIeS control systems can go into over-voltage shutdown should the supplied dc power exceed 145 V dc.
• The 125 V dc battery must be floating with respect to earth. This arrangement eliminates a hard ground on both the
positive and negative bus. A single ground fault applied to the system can pass current defined by the centering resistor
value and dc bus magnitude. Shift in bus voltage, in respect to earth, can then be detected to indicate a ground fault.
• Ground fault current in a floating battery system is defined by the fixed centering resistance value. The control system is
classified as non-hazardous Live because the ground fault current is below dangerous levels.
• The DACA module is designed to coordinate power delivery with a 125 V dc battery. One or two DACA modules,
powered by a reliable ac power source, could be used to provide backup power if battery failure occurs.

125 V dc Branch Circuit Protection

JPDD provides branch circuit protection for the 125 V dc power system. JPDD has six switched and fused dc outputs (12
fuses of type depending on
304 GEH-6855_Vol_II
board revision).
GEH-6855_Vol_II Mark VIeS Functional Safety Systems Volume II
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