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Grounding versus Bonding



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 to a suitable grounding electrode [250.50] in accordance with the following:

(1) Accessible Location. A grounding electrode conductor must connect the grounded neutral conductor to the grounding electrode and this connection can be made at any accessible location, from the load end of the service drop or service lateral, up to and including the service disconnecting means. Figure 250.51

Author's Comment: Some inspectors require the grounding electrode conductor to terminate at the meter enclosure, while other inspectors insist that the grounding electrode conductor terminate at the service disconnect.

The Code allows this grounding (earthing) connection to be made at either of these locations.
(4) Main Bonding Jumper. When the grounded neutral conductor is bonded to the service disconnecting means [250.24(B)] by a wire or busbar [250.28], the grounding electrode conductor can terminate to either the grounded neutral terminal or the equipment grounding terminal within the service disconnect.

(5) Load-Side Neutral-to-Case Bonding. A neutral-to-case bond cannot be made on the load side of the service disconnecting means, except as permitted for separately derived systems [250.30(A)(1)] or separate buildings [250.32(B)(2)] in accordance with 250.142. Figure 250.52

Author's Comment: If an improper neutral-to-case bond is made on the load side of service equipment, dangerous objectionable current will flow on conductive metal parts of electrical equipment in violation of 250.6(A). Objectionable current on metal parts of electrical equipment can cause electric shock and even death from ventricular fibrillation. Figure 250.53
(B) Main Bonding Jumper. An unspliced main bonding jumper complying with 250.28 must be installed between the grounded neutral terminal and the metal parts of the service disconnecting means enclosure in accordance with 250.24(C).

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