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What is Bonding?

Bonding [100]. The permanent joining of metal parts together to form an electrically conductive path that has the capacity to conduct safely any fault current likely to be imposed on it. See Image Above !

Mike's Comment: Bonding is accomplished by the use of conductors, metallic raceways, connectors, couplings, metallic-sheathed cables with fittings, and other devices recognized for this purpose [250.11].

Bonding Jumper [100]. A conductor properly sized in accordance with Article 250 that ensures electrical conductivity between metal parts of the electrical installation.

Effective Ground-Fault Current Path [250.2]. An intentionally constructed, permanent, low-impedance conductive path designed to carry fault current from the point of a ground fault on a wiring system to the electrical supply source.

The effective ground-fault current path is intended to help remove dangerous voltage from a ground fault by opening the circuit overcurrent protective device.

Equipment Grounding Conductor [100]. The low-impedance fault-current path used to bond metal parts of electrical equipment, raceways, and enclosures to the effective ground-fault-current path at service equipment or the source of a separately derived system.

Author’s Comments:
•The purpose of the equipment grounding (bonding) conductor is to provide the low-impedance fault-current path to the electrical supply source to facilitate the operation of circuit overcurrent protection devices in order to remove dangerous ground-fault voltage on conductive parts [250.4(A)(3)]. Fault current returns to the power supply (source), not the earth!

•According to 250.11, the equipment grounding (bonding) conductor must be one or a combination of the following: Figure 250–5

Wire Type. A bare or insulated conductor [250.11(1)]

Rigid Metal Conduit [250.11(2)]

Intermediate Metal Conduit [250.11(3)]

Electrical Metallic Tubing [250.11(4)]

Listed Flexible Metal Conduit as limited by 250.11(5)

Listed Liquidtight Flexible Metal Conduit as limited by 250.11(6)

Armor of Type AC cable [250.11(]

Armor of Type MC cable as limited by 250.11(10)

Metallic Cable Trays as limited by 250.11(11) and 392.8

Electrically continuous metal raceways listed for grounding [250.11(13)]

Surface Metal Raceways listed for grounding [250.11(14)]

(4) Bonding Conductive Materials to an Effective Ground-Fault Current Path. To remove dangerous voltage from ground faults, electrically conductive metal water piping systems, metal sprinkler piping, metal gas piping, and other metal-piping systems, as well as exposed structural steel members that are likely to become energized, must be bonded to an effective ground-fault current path. Figure Above

Author’s Comment: The phrase "likely to become energized" is subject to interpretation by the authority having jurisdiction.

(5) Effective Ground-Fault Current Path. Metal raceways, cables, enclosures, and equipment, as well as other electrically conductive materials that are likely to become energized, must be installed in a manner that creates a permanent, low-impedance fault-current path that facilitates the operation of the circuit overcurrent device. Figure 250–22

Author’s Comment: To assure a low-impedance ground-fault current path, all circuit conductors must be grouped together in the same raceway, cable, or trench [300.3(B), 300.5(I), and 300.20(A)]. Figure 250–23

The earth is not considered an effective ground-fault current path. from my portions of this educational moment on grounding the gas piping as shown above.

Lets examine Art 250.104(B)- Other Metal Piping

Other Metal Piping Systems- Metal piping systems , such as gas or air piping which may become energized, SHALL BE bonded to the service equipment enclosure, the grounded ( neutral ) service conductor, or the grounding electrode or grounding electrode conductor where the grounding electrode is of sufficient size. The bonding jumper SHALL BE sized in accordance with Table 250.122 using the rating of the circuit that may be energizing the piping. The equipment grounding ( bonding ) conductor for the circuit that may be energized the piping can serve as the bonding means.

Special thanks to Mike Holt!

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