Grounding

The following are grounding requirements for systems, circuits, and equipment.

Systems to Be Grounded

Systems that supply premises wiring typically must be grounded. Alternating current (AC) systems from 50 volts to 1,000 volts must be grounded under certain circumstances, such as if a service conductor is uninsulated.

Conductors to Be Grounded

The following conductors for AC premises wiring systems must be grounded:

• One conductor of a single-phase, two-wire system
• The neutral conductor of a single-phase, three-wire system
• The common conductor of a multiphase system having one wire common to all phases
• One phase conductor of a multiphase system where one phase is grounded
• The neutral conductor of a multiphase system in which one phase is used as a neutral conductor

Grounding Connections

For a grounded system, a grounding electrode conductor must be used to connect both the equipment grounding conductor and the grounded circuit conductor to the grounding electrode. For an ungrounded service-supplied system, the equipment grounding conductor must be connected to the grounding electrode conductor at the service equipment. Depending on the type of system, different connection requirements apply.

Supports, Enclosures, and Equipment That Must Be Grounded

Metal cable trays, raceways, and enclosures for conductors and metal enclosures for service equipment must be grounded. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and metal outlet or junction boxes that are part of the circuit for these appliances also must be grounded.

Exposed noncurrent-carrying metal parts of fixed equipment, and exposed noncurrent-carrying metal parts of cord- and plug-connected equipment that may become energized must be grounded under certain conditions set out in 29 CFR 1910.304.

Nonelectrical Equipment

The metal parts of various nonelectrical equipment must also be grounded. For example, the hand-operated metal shifting ropes or cables of electric elevators must be grounded.

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