In a two-circuit, shared-neutral arrangement on a 120/240 V single-phase system, the neutral current is

In a two-circuit, shared-neutral arrangement on a 120/240 V single-phase system, the neutral current is

• A. the sum of currents
• B. zero current
• C. only one circuit current
• D. the difference of currents

Answer: (D)

In a two-circuit shared-neutral on a 120/240 V single-phase system, the neutral current is the difference between the currents in the two hot legs. The two hot legs are 180 degrees out of phase, so their currents oppose each other in the neutral conductor. The neutral therefore carries only the unbalanced portion of the load, with magnitude equal to |I1 − I2|. If the loads on both legs are equal, neutral current is zero; if one leg carries more current, the neutral carries that excess. It’s not the sum of the currents, because the opposite-phase currents cancel in the neutral, and it’s not limited to one circuit’s current, since any imbalance between the two legs must flow through the neutral.

In a two-circuit shared-neutral on a 120/240 V single-phase system, the neutral current is the difference between the currents in the two hot legs. The two hot legs are 180 degrees out of phase, so their currents oppose each other in the neutral conductor. The neutral therefore carries only the unbalanced portion of the load, with magnitude equal to |I1 − I2|. If the loads on both legs are equal, neutral current is zero; if one leg carries more current, the neutral carries that excess. It’s not the sum of the currents, because the opposite-phase currents cancel in the neutral, and it’s not limited to one circuit’s current, since any imbalance between the two legs must flow through the neutral.