Three ungrounded and one grounded conductor are installed in a single conduit from a 120/208 V, 3-phase, 4-wire panelboard. By NEC, these conductors are a multiwire branch circuit.

Three ungrounded and one grounded conductor are installed in a single conduit from a 120/208 V, 3-phase, 4-wire panelboard. By NEC, these conductors are a multiwire branch circuit.

• A. True
• B. False
• C. Not possible
• D. Not defined

Answer: (A)

In NEC terms, a multiwire branch circuit is any branch circuit that has two or more ungrounded conductors sharing a common neutral. Here, you’ve got three ungrounded conductors (hots) and one grounded conductor (neutral) all in the same conduit fed from a 120/208 V, 3-phase, 4-wire panelboard. That means there are multiple hot conductors returning on a single neutral, so it qualifies as a multiwire branch circuit. In a 120/208 V 3-phase system, each hot to neutral delivers 120 V, and the neutral only carries the imbalance between the currents on the hot conductors. The neutral current is the vector sum of the three phase currents, which means it can carry significant current if the loads are unbalanced. An important safety point: all ungrounded conductors of a MWBC must be disconnectable by a single means of disconnect. Practically, that means the breakers feeding the three hots should be tied or a common-trip device used, so all hots can be shut off simultaneously. So, the statement is true.

In NEC terms, a multiwire branch circuit is any branch circuit that has two or more ungrounded conductors sharing a common neutral. Here, you’ve got three ungrounded conductors (hots) and one grounded conductor (neutral) all in the same conduit fed from a 120/208 V, 3-phase, 4-wire panelboard. That means there are multiple hot conductors returning on a single neutral, so it qualifies as a multiwire branch circuit.

In a 120/208 V 3-phase system, each hot to neutral delivers 120 V, and the neutral only carries the imbalance between the currents on the hot conductors. The neutral current is the vector sum of the three phase currents, which means it can carry significant current if the loads are unbalanced.

An important safety point: all ungrounded conductors of a MWBC must be disconnectable by a single means of disconnect. Practically, that means the breakers feeding the three hots should be tied or a common-trip device used, so all hots can be shut off simultaneously.

So, the statement is true.