The number of handsets used in parallel should not exceed __.

• A. 2
• B. 3
• C. 5
• D. 4

Answer: (D)

In a sound-powered telephone circuit, all handsets connected in parallel share the same line and the same sound source. Each additional handset adds more load to the line, which lowers the voltage and available current for everyone on that circuit. Because these systems rely on the energy generated by the operator’s voice (no external power), keeping the total load within a safe range is crucial for maintaining a clear, intelligible signal.

Limiting the number of handsets in parallel to four strikes the right balance between having enough devices available for operation and preserving enough signal strength for readability in noisy environments. Using more than four would push the line beyond what the transmit/receive components and the line can reliably support, leading to weaker signals, more distortion, and poorer communication. Fewer handsets keep the signal strong but don’t change the fundamental rule—the maximum is four.