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 these appliances must be grounded (bonded) to an effective ground-fault current path by an equipment grounding (bonding) conductor of a type specified in 250.118 [250.134(A)]. Figure 250–181
CAUTION: Ranges, dryers, and ovens have their metal cases bonded to the grounded neutral conductor at the factory. This neutral-to-case bond must be removed when these appliances are installed in new construction, and a 4-wire cord and receptacle must be used.Exception: For existing branch-circuit installations, where an equipment grounding (bonding) conductor isn’t present in the outlet box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet boxes that are part of the circuit for these appliances can be grounded (bonded) to the grounded neutral conductor if all the following conditions are met: Figure 250–182
(1) The circuit is 120/240V or 120/208V.
(2) The grounded neutral conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
(3) The grounded neutral conductor is insulated, or it’s uninsulated and part of a Type SE cable and the branch circuit originates at service equipment.
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