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Grounding versus Bonding

PART I.

Sections

250.6 Objectionable Current.

(A) Preventing Objectionable Current. To prevent a fire, electric shock, or improper operation of circuit-protection devices or sensitive equipment, electrical systems and equipment must be installed in a manner that prevents objectionable current from flowing on conductive materials, electrical equipment, or grounding and bonding paths.

Author’s Comment: Objectionable current occurs because of improper neutral-to-case bonds and wiring errors.
Improper Neutral-to-Case Bond [250.142]

Panelboards. Objectionable current will flow on metal parts when the grounded neutral conductor is bonded to the metal case of a panelboard that is not part of service equipment. Figure 250–28

Disconnects. Objectionable current will flow on metal parts when the grounded neutral conductor is bonded to the metal case of a disconnecting means that is not part of service equipment. Figure 250–29

Separately Derived Systems. Objectionable current will flow on metal parts when the grounded neutral conductor is bonded at the transformer as well as to the metal case on the load side of the transformer. Figures 250–30 and 250–31


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