🔍 Key Concepts

• Schematic symbols for mechanically-operated vs electrically-operated contacts • How a master switch (MS) controller is typically shown in crane/hoist control diagrams • Difference between contacts moved by a coil/relay and those moved directly by an operator’s handle

💭 Think About

• Look at where all the MS1–MS6 contacts are located in the diagram. Are they inside a separate control device or scattered around the circuit like relay contacts? • Compare the MS contact symbols with the symbols for relay or contactor-operated contacts (like 1M, 2CR, 3CR). What is different about how they are grouped and drawn? • Ask yourself: when the operator moves the hoist/boom controller handle, what part of this diagram changes state directly because of that motion?

✅ Before You Answer

• Verify that MS1–MS6 are all drawn together in the left-hand block that represents the master switch mechanism, not near any coils. • Confirm that no operating coil symbol is labeled MS; all coils are labeled with M, CR, or T instead. • Check which exam choice best matches a device that is physically linked to the controller handle, rather than being pulled in magnetically by a coil.