 |
250.62 Grounding Electrode Conductor—Material. |
The grounding electrode conductor, or its jumpers, can be solid or stranded, insulated or bare, and it must be copper, except aluminum is permitted if . . . |
| |
250.64 Grounding Electrode Conductor Installation. |
(A) Aluminum Grounding Electrode Conductor. Aluminum grounding electrode conductors cannot be in contact with earth, masonry, or subjected to . . . |
| |
250.66 Grounding Electrode Conductor—Size. |
Except for a ground rod electrode [250.66(A)], a concrete-encased electrode [250.66(B)], or a ground ring electrode [250.66(C)], the grounding electro . . . |
| |
250.68 Grounding Electrode Conductor Termination. |
(A) Attachment Fitting. The grounding electrode attachment fitting must be accessible.
Exception 1: The grounding electrode attachment . . . |
| |
250.70 Grounding Electrode Conductor Termination Fitting. |
The grounding electrode conductor must terminate to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed cla . . . |
| |
250.50 Grounding Electrode System. |
All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure must be bonded together to form th . . . |
| |
250.52 Grounding (Earthing) Electrodes. |
(A) Electrodes Permitted for Grounding.
(1) Underground Metal Water Pipe Electrode. Underground metal water pipe in direct contact . . . |
| |
250.52 Grounding (Earthing) Electrodes Continued |
(6) Ground Plate Electrode. A buried iron or steel plate with not less than 1⁄4 in. of thickness, or a nonferrous (copper) metal plate no . . . |
| |
250.53 Installation of Grounding Electrode System. |
(A) Ground Rod Electrodes. Where practicable, ground rods must be embedded below permanent moisture level and must be free from nonconductive . . . |
| |
250.54 Supplementary Electrodes. |
A supplementary electrode is an electrode that is not required by the NEC. This electrode is not required to be bonded to the building or structure gr . . . |
| |
250.56 Resistance of Ground Rod Electrode. |
When the resistance of a single ground rod is over 25 ohms, an additional electrode is required to augment the ground rod electrode, and it must be in . . . |
| |
250.58 Common Grounding (Earthing) Electrode. |
Where a building or structure is supplied with multiple services or feeders as permitted by 225.30 and 230.2, the same electrode must be used to groun . . . |
| |
250.60 Lightning Protection System Grounding (Earthing) Electrode. |
The grounding electrode for a lightning protection system cannot be used for the building or structure grounding electrode system as required by 250.5 . . . |
| |
250.80 Service Enclosures. |
Metal raceways and enclosures containing service conductors must be grounded (bonded) to an effective ground-fault current path [250.4(A)(5)].
E . . . |
| |
250.86 Other Enclosures. |
Metal raceways and enclosures containing electrical conductors that operate at over 50V [250.112(I)] must be grounded (bonded) to an effective ground- . . . |
| |
250.92 Service Bonding. |
(A) Equipment and Raceways. The following metal parts must be service bonded to an effective ground-fault current path in accordance with 250 . . . |
| |
250.106 Lightning Protection System. |
Where a lightning protection system is installed, the lightning protection system must be bonded to the building or structure grounding electrode syst . . . |
| |
250.92 Service Bonding Continued |
(2) Threaded Fittings or Entries. Raceways containing service conductors are considered bonded to an effective ground-fault current path by thr . . . |
| |
250.94 Grounding (Bonding) of Communications Systems. |
An accessible bonding point must be provided at service equipment or the disconnecting means of separate buildings or structures for communications sy . . . |
| |
250.96 Bonding Other Enclosures. |
(A) Maintaining Effective Ground-Fault Current Path. All metal parts intended to serve as the effective ground-fault current path, such as ra . . . |
| |
250.97 Bonding 277V/480V. |
Metal raceways or cables, containing 277V or 480V circuits, terminating at ringed knockouts must be bonded to the metal enclosure with a bonding jumpe . . . |
| |
250.100 Bonding—Hazardous (Classified) Locations. |
Because of the explosive conditions associated with electrical installations in hazardous (classified) locations, electrical continuity of the effecti . . . |
| |
250.102 Bonding Jumper. |
(A) Bonding Material. Bonding jumpers must be of copper.
(B) Bonding Jumper Attachment. Bonding jumpers must terminate by exother . . . |
| |
250.104 Bonding of Piping Systems and Exposed Structural Metal. |
Author’s Comment: To remove dangerous voltage on metal parts from a ground fault, electrically conductive metal water piping systems, met . . . |
| |
250.104 Bonding of Piping Systems and Exposed Structural Metal Continued |
(D) Separately Derived Systems. Metal water pipe systems and structural metal that forms a building frame must be bonded in accordance with ( . . . |
| |
250.118 Types of Equipment Grounding (Bonding) Conductors. |
The equipment grounding (bonding) conductor, which serves as the effective ground-fault current path to the source, must be one or a combination of th . . . |
| |
250.118 Types of Equipment Grounding (Bonding) Conductors Continued |
(9) The copper metal sheath of Type MI cable.
(10) Type MC cable where listed and identified for grounding as follows:
a. Interlocked Type MC . . . |
| |
250.119 Identification of Equipment Grounding (Bonding) Conductor. |
Unless required to be insulated, equipment grounding (bonding) conductors can be bare.
Author’s Comment: Equipment grounding (bonding) . . . |
| |
250.122 Sizing Equipment Grounding (Bonding) Conductor. |
(A) General. The equipment grounding (bonding) conductor must be sized in accordance with Table 250.122, based on the ampere rating of the ci . . . |
| |
250.122 Sizing Equipment Grounding (Bonding) Conductor Continued |
(B) Increased in Size. When ungrounded circuit conductors are increased in size for any reason, the equipment grounding (bonding) conductor m . . . |
| |
250.126 Identification of Wiring Device Terminals. |
The terminal for the equipment grounding (bonding) conductor must be a:
(1) Green screw, hexagonal head, and not readily removable. Figure 250 . . . |
| |
250.130 Equipment Grounding (Bonding) Conductor Connections. |
(A) For Grounded Systems. The service disconnecting means supplied by a grounded utility system must have the grounded neutral service conduc . . . |
| |
250.134 Grounding (Bonding)—Fixed Equipment. |
Metal parts of fixed electrical equipment, raceways, and enclosures must be grounded (bonded) to an effective ground-fault current path in accordance . . . |
| |
250.140 Grounding (Bonding)—Ranges, Ovens, and Clothes Dryers. |
The frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet boxes that are part of the circuit for th . . . |
| |
250.142 Use of Grounded Neutral Conductor for Equipment Grounding (Bonding). |
Author’s Comment: To remove dangerous voltage on metal parts from a ground fault, the metal parts of electrical raceways, cables, enclosu . . . |
| |
250.146 Connecting Receptacle Grounding Terminal to Box |
Receptacles must have their grounding contacts connected to an effective ground-fault current path by bonding the receptacle’s grounding terminal to a . . . |
| |
250.146 Connecting Receptacle Grounding Terminal to Box Continued |
(C) Floor Boxes. Listed floor boxes are permitted to establish the bonding path between the device yoke and a grounded (bonded) outlet box.
. . . |
| |
250.148 Continuity and Attachment of Equipment Grounding (Bonding) Conductors to Boxes. |
Equipment grounding (bonding) conductors associated with circuit conductors that are spliced or terminated on equipment within a metal outlet box, mus . . . |
| |
250.20 Systems Required to be Grounded and Bonded |
Alternating-current systems (power supplies) must be grounded and bonded as provided in (A), (B), (C), or (D).
Author’s Comment: System grounding, th . . . |
| |
250.32 Buildings or Structures Supplied by a Feeder or Branch Circuit. |
(A) Grounding Electrode. To provide a path to earth for lightning, each building or structure must have its disconnecting means [225.31] grou . . . |
| |
250.32 Buildings or Structures Supplied by a Feeder or Branch Circuit Continued |
The equipment grounding (bonding) conductor, if of the wire type, must be sized in accordance with 250.122, based on the rating of the feeder protecti . . . |
| |
250.34 Generators—Portable and Vehicle-Mounted |
(A) Portable Generators. The frame of a portable generator isn’t required to be grounded to the earth if: Figure 250–88
(1) The g . . . |
| |
250.36 High-Impedance Grounded Neutral Systems. |
To limit fault current to a very low value, high-impedance grounded neutral systems have a resistor installed between the system and the metal parts o . . . |
| |
250.20 Systems Required to be Grounded and Bonded Continued |
(D) Separately Derived Systems. Separately derived systems that are required to be grounded (bonded) by 250.20(A) or (B), must be grounded an . . . |
| |
250.24 Grounding and Bonding at Service Equipment. |
(A) Grounding. Services supplied from a utility transformer that is grounded to the earth must have the grounded neutral conductor grounded t . . . |
| |
250.24 Grounding and Bonding at Service Equipment Continued |
(C) Grounded Neutral Conductor Required. Because electric utilities aren’t required to provide an equipment grounding (bonding) conductor to . . . |
| |
250.24 Grounding and Bonding at Service Equipment Continued |
Author’s Comments:
• A ground-fault cannot be cleared to remove dangerous voltage on the metal parts, metal piping, and structural steel . . . |
| |
250.28 Main Bonding Jumper and System Bonding Jumper. |
(2) Parallel Grounded Neutral Conductor. Where service conductors are paralleled, a grounded neutral conductor must be installed in each racewa . . . |
| |
250.30 Grounding and Bonding of Separately Derived AC Systems. |
Author’s Comment: A separately derived system is a premises wiring system with no direct electrical connection to conductors originating . . . |
| |
250.30 Grounding and Bonding of Separately Derived AC Systems Continued |
The system bonding jumper can be installed at the separately derived system, the first system disconnecting means, or any point in between the separat . . . |
| |
250.30 Grounding and Bonding of Separately Derived AC Systems Continued |
To prevent objectionable current from flowing onto metal parts of electrical equipment, as well as metal piping and structural steel, the grounding el . . . |
| |
250.6 Objectionable Current Continued |
Fire Hazard. When objectionable current flows on metal parts, a fire could occur because of elevated temperature, which can ignite adjacent com . . . |
| |
250.8 Termination of Grounding and Bonding Conductors. |
The termination of equipment grounding and bonding conductors must be by exothermic welding, listed pressure connectors of the set screw or compressio . . . |
| |
250.2 Definitions. |
Author’s Comment: Why is grounding so difficult to understand? One reason is because many do not understand the definition of many import . . . |
| |
250.2 Definitions Continued |
Ground (Earth) [100]. Earth or a conductive body that is connected to earth. Figure 250–6
Grounded [100]. Connected to eart . . . |
| |
250.2 Definitions Continued |
Grounding (Earthing) Electrode [100]. A device that establishes an electrical connection to the earth. Figure 250–11
Autho . . . |
| |
250.4 General Requirements for Grounding and Bonding. |
(A) Solidly Grounded Systems.
(1) Grounding Electrical Systems to the Earth. High-voltage system windings are grounded to the earth . . . |
| |
250.4 General Requirements for Grounding and Bonding Continued |
(4) Bonding Conductive Materials to an Effective Ground-Fault Current Path. To remove dangerous voltage from ground faults, electrically conduc . . . |
| |
250.4 General Requirements for Grounding and Bonding Continued |
To understand how a ground rod is useless in reducing touch voltage to a safe level, let’s answer the following questions:
What is touch volta . . . |
| |
250.6 Objectionable Current. |
(A) Preventing Objectionable Current. To prevent a fire, electric shock, or improper operation of circuit-protection devices or sensitive equ . . . |
| |
250.6 Objectionable Current Continued |
Wiring Errors
Objectionable current will flow on metal parts when the grounded neutral conductor from one system is connected to a circuit . . . |
