Final answer:
The statement is true; the neutral wire in a 3-wire circuit is crucial for parallel operation, and if it opens, the remaining circuit paths may act as if they are in series.
Step-by-step explanation:
When addressing the statement that when the neutral opens in a 3 wire circuit, the current flowing through the circuit will no longer be flowing in parallel but will act as a series circuit, it is true. In a three-wire system, the neutral wire has a significant role in providing a return path for the current and keeping the potential at zero volts, thereby making the system operate in parallel. If this wire opens, the current cannot flow back to the source through the intended neutral path, which may result in the remaining paths behaving as though they are in series, with devices being subject to the full line voltage split across them, which can be dangerous and cause equipment to operate outside of its safe voltage range.