Figure 4-3. An ungrounded system does not have a grounded (neutral) conductor routed between the supply

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phases and ground are subjected to 1.732 times the voltage they would experience on a solidly neutral

grounded system. (See Figure 4-3.)

Note: All ungrounded systems should be equipped with ground detectors and proper maintenance

applied to avoid, as far as practical, the overcurrent of a sustained ground fault on ungrounded

systems. If appropriate maintenance is not provided for ungrounded systems, a grounded system

should be installed to ensure that ground faults will be cleared and the safety of circuits, equipment,

and that personnel safety is ensured.

NEC Section 250-5 (b) Ex. 1-5

OSHA Section 29 CFR 1910.304 (f)

Figure 4-3. An ungrounded system does not have a grounded (neutral) conductor routed between the supply

transformer and the service equipment because the supply transformer is not earth grounded.

4.5.3 HIGH-IMPEDANCE GROUNDING

Electrical systems containing three-phase, three-wire loads, as compared to grounded neutral circuit

conductor loads, can be equipped with a high-impedance grounded system. High-impedance

grounded systems shall not be used unless they are provided with ground fault indicators or alarms,

or both, and qualified personnel are available to quickly locate and eliminate such ground faults.

Ground faults must be promptly removed or the service reliability will be reduced. See NEC Section

250-27 for requirements pertaining to installing a high-impedance grounding system. (See Figure 4-4.)

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