Grounded Systems

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