Article 250: Grounding and Bonding

Article 250 covers the requirements for grounding and bonding of electrical installations. It also specifies the conditions under which guards, isolation, or insulation may be substituted for grounding.

I. General (250.1 Through 250.14)

This part describes the purpose of grounding and bonding, prevention of objectionable currents over the grounding path, effective methods for making grounding and bonding connections, and protection of ground clamps and fittings.

II. System Grounding (250.20 Through 250.36)

This part describes which systems are required to be grounded, which systems are permitted but not required to be grounded, and which systems are prohibited from being grounded.

III. Grounding Electrode System and Grounding Electrode Conductor (250.50 Through 250.70)

This part describes the requirements for grounding electrodes and grounding electrode conductors.

IV. Enclosure, Raceway, and Service Cable Connections (250.80 Through 250.86)

This part describes the requirements for grounding metal enclosures and raceways.

V. Bonding (250.90 Through 250.106)

This part describes the requirements for bonding metal parts of equipment enclosures on both grounded and ungrounded electrical systems, metal piping systems, exposed structural steel, and lightning protection systems.

VI. Equipment Grounding and Equipment Grounding Conductors (250.110 Through 250.126)

This part first describes the requirements for grounding equipment that is fixed in place or connected by permanent wiring methods. Then it describes the requirements for equipment grounding conductors.

VII. Methods of Equipment Grounding (250.130 Through 250.148)

This part describes what is required to be grounded as well as the basic properties of equipment grounding conductors. Other topics covered include the following:

• Raceway or cable armor

• Equipment fastened in place or connected by permanent wiring methods

• Equipment considered effectively grounded

• Frames of ranges and clothes dryers

• Use of a grounded circuit conductor for equipment grounding

• Connecting receptacle grounding terminals

• Isolated grounded receptacles

• Attachment of equipment grounding conductors to boxes

VIII. Direct-Current Systems (250.160 Through 250.169)

This part describes the requirements for grounding direct-current systems. However, where this part does not specifically require or prohibit an aspect of grounding dc systems, another part or section of Article 250 not specifically intended for ac systems may apply.

IX. Instruments, Meters, and Relays (250.170 Through 250.178)

This part provides the requirements for grounding devices such as current and potential transformers, meters, and relays.

X. Grounding of Systems and Circuits of 1 kV and Over (High Voltage) (250.180 Through 250.190)

This part describes the requirements for derived neutral systems, solidly grounded neutral systems, and impedance grounded neutral systems, and for grounding of systems supplying portable or mobile equipment. This includes the requirements for equipment associated with non–current-carrying metal parts of all high-voltage installations.

Table 250.3  Additional Grounding and Bonding Requirements