HVACR317 – Core Refrigeration

1. HVACR317 – CoreRefrigeration Motor Protection

2. Overloads • The overload is designed too: • Shut down the motor circuit due to heat or high amperage draw.

3. Motor Starter Types • Part of the motor starter package (start components). • The contactor has built in overloads. • The overload consists of: • Ratchet wheel • Solder • Heater • Spring

4. Motor Starter Types • Overload Operation: • The overload is activated by a heater wire. • Excessive current which produces excess heat, melts the solder and the ratchet wheel opens the contacts. • Heater is line duty – is in the main circuit. • Contacts are pilot duty, is in the control circuit.

5. 4 Wire Overloads • Consists of: • A current sensing coil • Contacts

6. 4 Wire Overloads • Operation: • Coil senses amperage • Excessive amperage will open contacts. • Contacts are usually wired in series with motor contactors. • Used mainly with three phase motors.

7. Bimetal Overloads • A bimetal strip opens and closes contacts. • Commercial type: • Use a heater • The heater and contacts may be in series or parallel.

8. Bimetal Overloads • Domestic Type • Mounts to compressor • May be bimetal only or bimetal with heater. • Operation • Current flow and unit temperature combine to open contacts. • Contacts automatically reset • Overload is line duty – directly in circuit.

9. Sizing Overloads • All are rated by amperage and horsepower. • All have normal amperage draw of 115%-125% of full load amperage for a set amount of time.

10. Newer Methods • Solid State Thermistors • As heat is produced resistance changes and changes the current flow to a micro processor. • Information is received by the microprocessor and in turn shuts down the unit.