* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Electrical Installation Practice 2
Brushed DC electric motor wikipedia , lookup
Thermal runaway wikipedia , lookup
Stepper motor wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Mains electricity wikipedia , lookup
Current source wikipedia , lookup
Induction motor wikipedia , lookup
Ground (electricity) wikipedia , lookup
Electrical substation wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Skin effect wikipedia , lookup
Three-phase electric power wikipedia , lookup
Buck converter wikipedia , lookup
Electric machine wikipedia , lookup
Opto-isolator wikipedia , lookup
Stray voltage wikipedia , lookup
Portable appliance testing wikipedia , lookup
Circuit breaker wikipedia , lookup
Galvanometer wikipedia , lookup
Alternating current wikipedia , lookup
Protective relay wikipedia , lookup
Electrical wiring in the United Kingdom wikipedia , lookup
Content • • • • • • Operating principles of RCDs Types of RCDs Circuit arrangement of RCDs RCD current rating Wiring rules requirements concerning RCDs RCD selection Inside a RCD Inside a RCD Toroidal Transformer Tripping Relay Trip Relays Three Types • Magnetically Held • Electronic • Electro-mechanical 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 Trips on +ve cycle only • Saturation Trips on both +ve and –ve of the cycle How a RCD Works With a Fault How a RCD Works With a Fault 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 Causes of Unwanted Tripping • Standing Leakage Currents • Electrical Disturbances • Installation practices & Faults Standing Leakage Currents Is insulation is perfect? 230V 1MΩ AS/NZS 3000:2007 Clause 8.3.6.2 Page 321 = 0.23 mA Class I appliances may legally have up to 5mA What about sheathed heating elements? 230V 0.01MΩ = 23 mA AS/NZS 3000:2007 Clause 8.3.6.2 Page 321 Electrical Disturbances Caused by: • Lightning strikes Natural • Switching transients Manmade Lightning Strikes Generally cause transients in the form of: • High Voltage • High frequency Switching Transients What happens when a magnetic field changes? Generation of: Reduce the Xc of the circuit • High Voltages I • High frequencies X c f V I Xc Leakage current increases Two insulated conductors running together Switching Transients • Starting induction motors have a very low PF • High inrush currents 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 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 Relay Types Type III RCDs and relays with a trip current (IΔn) exceeding 30mA but not 300mA But without “Selective Tripping” Time Delay Relay Types Type IV RCDs and relays with a trip current (IΔn) exceeding 30mA but not 300mA With “Selective Tripping” Time Delay But What Type of Current? Type and shape of current will affect the tripping AS/NZS 3000:2007 time of an RCD 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 RCD Housings 2 Pole Does not trip due to over current Connecting a 2 Pole RCD Neutral link Protected Neutral link 4 Pole RCD Single Phase Circuit X2 OR 3 Phase + Neutral Note Some RCDs are Polarised RCD Power Point Combination RCD MCB RCD + MCB = 3 Modules OR RCD/MCB = 2 Modules Toroidal RCD Output Used to supply Trip Coil on a Circuit breaker