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DOE-HDBK-1092-98
system disconnecting means or overcurrent devices. Where the main system disconnecting means
is adjacent to the generator, converter, or transformer supplying a separately derived system, the
grounding connection to the system grounded conductor can be made at or ahead of the system
disconnecting means.
The preferred grounding electrode for a separately derived system is the nearest effectively grounded
structural metal member of the building or the nearest effectively grounded water pipe. If neither is
available, concrete-encased electrodes or made electrodes are permitted.
In a grounded, separately derived system, the equipment grounding conductors shall be bonded to
the system-grounded conductor and to the grounding electrode at or ahead of the main system
disconnecting means or overcurrent protection device. The equipment grounding conductor should
always be connected to the enclosure of the supply transformer, generator, or converter.
The grounding electrode conductor, the main bonding jumper, the grounded conductor, and the
equipment grounding conductor are calculated, sized, and selected by the rules listed in Sections 4.7
through 4.10. (See Figure 4-7.)
NEC Section 250- 26
OSHA Section 29 CFR 1910.304 (f) (3) (ii)
Figure 4-7. The grounded (neutral) conductor can be used to carry both normal neutral current and abnormal
ground fault current.
4.13 GROUNDING ELECTRODE SYSTEM
If 10 ft or more of metal water pipe is in the earth, the water pipe is considered the grounding
electrode, but it shall be supplemented by an additional electrode. NEC Section 250-81 lists four
types of electrodes. If one or all are available, they shall be bonded together to make up the grounding
electrode system. The bonding jumper that connects these electrodes shall be at least as large as the
4-16


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