Which contact(s) are open when the switch is in the START mode?

• A. 1 & 3
• B. 2 & 4
• C. 1 & 2
• D. 3 & 4

Answer: (B)

When a switch has both normally open (NO) and normally closed (NC) contacts, moving it to the START position changes which paths are energized. In START, the mechanism opens the contacts that are normally closed, interrupting those circuits. So the contacts that end up open in START are the two normally closed ones. The diagram reflects this by showing those NC contacts separated in the START position. (The normally open contacts, in contrast, would close to allow the start circuit to energize.)