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Grounding versus Bonding

PART I.

Sections

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 of a different system. Figure 250–32

Objectionable current will flow on metal parts when the equipment grounding (bonding) conductor is used as a grounded neutral conductor.

Example: A 240V time-clock motor is replaced with a 120V time-clock motor and the equipment grounding (bonding) conductor is used to feed one side of the 120V time clock. Another example is a 120V water filter wired to a 240V well-pump motor circuit, with the equipment grounding (bonding) conductor used for the neutral. Figure 250–33

Using the equipment grounding (bonding) conductor for the neutral is also seen in ceiling fan installations where the bare equipment grounding (bonding) conductor is used as a neutral and the white wire is used as the switch leg for the light, or where a receptacle is added to a switch outlet that doesn’t have a neutral conductor. Figure 250–34

Author’s Comment: Neutral currents always flow on a community metal underground water piping system because the grounded neutral conductor from each service is grounded to the underground metal water pipe. Figure 250–35
Dangers of Objectionable Current

Objectionable current on metal parts can cause electric shock, fires, and improper operation of sensitive electronic equipment and circuit-protection devices.

Shock Hazard. When objectionable current flows on metal parts, electric shock and even death can occur (ventricular fibrillation) from elevated voltage on the metal parts. Figure 250–36


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