Electrical Installation Practice 2

1. Electrical Installation Practice 2 LSEGG304A 9080D

2. Protection DevicesRCDs

3. Content • Operating principles of RCDs • Types of RCDs • Circuit arrangement of RCDs • RCD current rating • Wiring rules requirements concerning RCDs • RCD selection

4. Inside a RCD

5. Inside a RCD Toroidal Transformer Tripping Relay

6. Trip Relays Three Types • Magnetically Held • Electronic • Electro-mechanical

7. Magnetically Held • Magnet holds trip circuit closed against a spring • Fault causes a current to flow in a coil around magnet • Magnetic field is reduced • Spring is stronger than magnetic field and trips breaker • Polarised • Saturation Trips on +ve cycle only Trips on both +ve and –ve of the cycle

8. How a RCD Works With a Fault

9. How a RCD Works With a Fault

10. What Must A RCD Do? • Detect leakage current up to its rated value • Switch of rapidly when such leakage current is detected • Ignore leakage currents 50% below its rated value • Discriminate between earth leakage current and other line disturbances

11. Causes of Unwanted Tripping Standing Leakage Currents Electrical Disturbances Installation practices & Faults

12. Standing Leakage Currents Is insulation is perfect? AS/NZS 3000:2007 Clause 8.3.6.2 Page 321 230V = 0.23 mA 1MΩ Class I appliances may legally have up to 5mA What about sheathed heating elements? AS/NZS 3000:2007 Clause 8.3.6.2 Page 321 230V = 23 mA 0.01MΩ

13. Electrical Disturbances Caused by: • Lightning strikes • Switching transients Natural Manmade

14. Lightning Strikes Generally cause transients in the form of: • High Voltage • High frequency

15. Switching Transients What happens when a magnetic field changes? • Generation of: • High Voltages • High frequencies Reduce the Xc of the circuit Leakage current increases Two insulated conductors running together

16. Switching Transients • Starting induction motors have a very low PF • High inrush currents

17. Relay Types Type I RCDs and relays with a trip current (IΔn) not exceeding 10 mA. • Found in high risk areas such as: • Hospitals • Doctors rooms • Dialysis rooms • Dentists rooms • Kindergartens

19. Relay Types Type II RCDs and relays with a trip current (IΔn) exceeding 10mA but not 30mA General purpose: As per AS/NZS 3000:2007

21. Relay Types Type III RCDs and relays with a trip current (IΔn) exceeding 30mA but not 300mA But without “Selective Tripping” Time Delay

23. Relay Types Type IV RCDs and relays with a trip current (IΔn) exceeding 30mA but not 300mA With “Selective Tripping” Time Delay

25. But What Type of Current? Type and shape of current will affect the tripping time of an RCD AS/NZS 3000:2007 Clause 2.6.2.2 Page 97 AC Guaranteed for only AC operation A Will take some pulsating DC current B AC up to 1000Hz, pulsating DC, and DC S Selective RCD

26. RCD Housings 2 Pole Does not trip due to over current

27. Connecting a 2 Pole RCD Neutral link Protected Neutral link

28. 4 Pole RCD

29. Single Phase Circuit X2 OR 3 Phase + Neutral Note Some RCDs are Polarised

30. RCD Power Point

31. Combination RCD MCB

32. RCD + MCB = 3 Modules OR RCD/MCB = 2 Modules

33. Toroidal RCD Output Used to supply Trip Coil on a Circuit breaker