In a 1 phase, 120/240V service, which size should the neutral conductor be if a 100A load is connected across A and B, and a 50A load across A and N?

In a single-phase 120/240V service, the neutral conductor's size is crucial for handling the current that may flow through it due to the loads connected to the system.

When there is a 100A load connected between conductors A and B, this is a 240V load. This doesn't directly affect the neutral conductor size because the current flowing between A and B does not return through the neutral. However, when there is also a 50A load between conductor A and the neutral, the neutral conductor must be capable of carrying the return current from this load.

In this case, the total current that could flow back through the neutral is the current from the A-N load, which is 50A. The National Electrical Code (NEC) provides guidelines for determining the appropriate size of the neutral conductor, taking into account not just the maximum load but also safety factors.

Typically, the neutral conductor should be sized to carry the maximum anticipated return current under normal operating conditions. In this instance, for a 50A load returning through the neutral, a gauge size of 6 AWG would be appropriate to ensure it can safely handle the return current without overheating. Additionally, it offers a buffer for potential overload.

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