Q. What are the Code requirements for overcurrent protection for ungrounded conductors?
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A. A fuse or circuit breaker must be connected in series with each ungrounded conductor [240.15(A)]. Circuit breakers must automatically (and manually) open all ungrounded conductors of the circuit, except as follows [240.15(B)]:
1) Multiwire Branch Circuits. Individual single-pole breakers with identified handle ties are permitted for a multiwire branch circuit that only supplies line-to-neutral loads.
Author’s comments: According to Art. 100, “Identified” means recognized as suitable for a specific purpose, function, or environment by listing, labeling, or other means approved by the authority having jurisdiction. This means handle ties made from nails, screws, wires, or other nonconforming materials aren’t suitable. In addition, single-pole AFCI or GFCI circuit breakers aren’t suitable for protecting multiwire branch circuits. AFCI or GFCI circuit breakers for multiwire branch circuits must be of the 2-pole type.
2) Single-Phase, Line-to-Line Loads. Individual single-pole circuit breakers rated 120/240V with handle ties identified for the purpose are permitted on each ungrounded conductor of a branch circuit that supplies single-phase, line-to-line loads.
3) Three-Phase, Line-to-Line Loads. Individual single-pole breakers rated 120/240V with handle ties identified for the purpose are permitted on each ungrounded conductor of a branch circuit that serves three-phase, line-to-line loads on systems not exceeding 120V to ground.