🔍 Key Concepts

• How overload protection is shown in motor starter diagrams (heaters in the power circuit vs contacts in the control circuit) • The symbol difference between normally open and normally closed contacts in control schematics • How a control circuit uses an overload device to de‑energize the motor starter coil when an overload occurs

💭 Think About

• Look at where terminals 3 and 4 are located: are they in the power circuit feeding the motor, or in the low‑current control circuit feeding the starter coil? What type of device is normally placed there? • Compare the symbol at 3–4 with the symbols used for the overloads in the three motor lines (L1–L3). Are they identical heaters, or does one represent a contact operated by those heaters? • Ask yourself: when an overload happens, what has to open in the control circuit to drop out the motor starter coil, and in what ‘normal’ state (open or closed) must that contact be drawn on the schematic?

✅ Before You Answer

• Verify whether the symbol at 3–4 is drawn as a contact (two blades with a gap) or as a heater element in series with the motor. • Confirm if the contact at 3–4 is shown closed in the normal (non‑tripped) condition or open; this tells you if it’s ‘normally closed’ or ‘normally open’. • Check that the heaters labeled OL in the line circuit and the device at 3–4 work together: the heaters sense current in the motor leads, and a separate control contact changes state to stop the motor.