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DOE-HDBK-1092-2004
4.5.1
GROUNDED SYSTEMS
Grounded systems are equipped with a grounded conductor that is required to be run to each
service disconnecting means. The grounded conductor can be used as a current-carrying
conductor to accommodate all neutral related loads. It can also be used as an equipment
grounding conductor to clear ground faults ahead of the service disconnecting means.
A network of equipment grounding conductors is routed from the service equipment enclosure
to all metal enclosures throughout the electrical system. The equipment grounding conductor
carries fault currents from the point of the fault to the grounded bus in the service equipment
where it is transferred to the grounded conductor. The grounded conductor carries the fault
current back to the source and returns over the faulted phase and trips open the overcurrent
protection device.
Note: A system is considered grounded if the supplying source, such as a transformer or
generator is grounded in addition to the grounding means on the supply side of the service
equipment disconnecting device for separately derived systems.
The neutral of any grounded system serves two main purposes: (1) it permits the utilization of
line-to-neutral voltage and thus will serve as a current-carrying conductor to carry any neutral
current, and (2) it plays a vital role in providing a low-impedance path for the flow of fault
currents to facilitate the operation of the overcurrent devices in the circuit. (See Figure 4-2.)
Consideration should be given to the sizing of the neutral conductor for certain loads due to the
presence of harmonic currents.
NEC 250.130
Figure 4-2. A grounded system is equipped with a grounded (neutral) conductor
routed between the supply transformer and the service equipment.
4-4


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