8. Residual Current Device RCD Safety Switch LOAD N A/s Supply When the circuit is in good condition. (No Earth Faults) (I active = I neutral) = No Flux = No Induced EMF Supply to the Load is Maintained I A I N
9. RCD with Earth Fault LOAD N A/s Supply When an Earth Faults occurs. (I active I neutral) = Flux in Core = Induced EMF The fault is Isolated
10. Safety Switch N A/s Supply Not Earthed A person can receive a shock with a “Safety Switch” installed Another point to consider: An RCD rated at 40Amps will not trip (like a C/B) if say 52Amps will to flow through the device.
84. The Fault Loop 1. The impedance needs to be low enough, to allow a high enough fault current, to operate the protective device, within a given time period. (6.3.3.2.2) 2. The Earth Loop Impedance is matched to the Protective Device Tripping Characteristics. 3 Phase Supply N/L
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87. Earth System ♦ Z LOOP = Z ACTIVE + Z EARTH + Z NEUTRAL + Z TX ♦ All these will limit current and dictate the fault current that will flow. Load N/L 16A MEN Link must be left intact
98. Earth System Load 16A N/L With 80% of voltage drop here in a fault, the FSC must have 80% of the total Fault Loop Impedance. Where the length and CSA of the mains is not known, we may assume that 80% of the voltage drop under fault conditions will occur in the final sub-circuit (B5.2.1b).
104. But what if the cable/CB size is not there on that table?
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106. Say, 300mm 2 orange circ. cable supplying a 415V, 350A, 3-phase motor through underground conduit 140mtrs away… 7. Measure the actual loop impedance. MAIN SWITCHBOARD Load Z = V/I A V I 5A
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112. Remember the last question? Q: Why do we want a low resistance earth wire? To CREATE a high enough fault current to trip the protective device. To ensure that we do create a high enough fault current, fault loop impedance must be low enough.
114. A Simplified Circuit We need to look at a complete loop (circuit) 3 Phase Supply The current path includes the: Supply Transformer, Distribution System, Mains, Protection Device, Final Sub-Circuit including the Load N/L
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116. 3 Phase Supply There will always be more than 80% of the Nominal Voltage AS/NZ3000:2000 B5.2.1 b Zext Zint Zint = 0.8 Uo I a B5.2.1
122. Recent studies have shown that 95% of electricians do not fully understand the MEN system. This figure comes from the Electrical Contractors Association of Queensland who were conducting training sessions throughout Queensland during 1998. They asked electricians to draw a MEN system and explain it. Only 5% could!!! MEN System
123. MEN Connection Consumer Mains MAIN SWITCHBOARD Circuit Protective Devices Earth Link Neutral Link Main Switch
124. MEN Connection Circuit Protective Devices Consumer Mains MAIN SWITCHBOARD Neutral Link Main Switch So why do we earth the neutral at the board?
125. Load Direct Earthing System 16A Q: Will the fuse blow? FAULT R TOTAL = 23.5 I FAULT = V/R = 240/23.5 10A 0.3 0.2 23
126. Load MEN Earthing System 0.3 0.2 16A R TOTAL = 1 Q: Will the fuse blow? 0.5 I FAULT = V/R = 240/1 = 240A N/L FAULT R RETURN = 0.5//23 0.5 23
127. Q: Why do we want a low resistance earth wire? To CREATE a high enough fault current to trip the protective device.
128. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Earth Link Neutral Link NORMAL LOAD CURRENT Typical Earth stake to Earth resistance = 30 - 2k Main Switch Load Low R Consumer Mains
129. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Earth Link Neutral Link FAULT CURRENT Main Switch Load A Low Resistance earth CREATES A high fault current. Low R
130. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Consumer Mains Earth Link Neutral Link What are the values given by AS3000 on earth resistance? Main Switch Load
131. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Consumer Mains Earth Link Neutral Link 2 maximum 2 maximum Main Switch Load
132. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Consumer Mains Earth Link Neutral Link Main Switch < 0.5 (6.3.3.2.2) Load “ The resistance of the protective earthing conductors shall be low enough to permit the passage of current necessary to operate the overcurrent protective device” (6.3.3.2.2)
134. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Earth Link Neutral Link Load OPEN CIRCUIT MEN Connection
135. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Earth Link Neutral Link NORMAL LOAD CURRENT Everything operates OK!!! Load
136. THEREFORE FAULT CURRENT WILL BE VERY LOW MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Main Switch Earth Link Neutral Link FAULT CURRENT But RESISTANCE TO EARTH IS USUALLY HIGH. Load
137. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Main Switch Earth Link Neutral Link FAULT CURRENT AND PROTECTION WILL NOT TRIP. Load
138. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Main Switch Earth Link Neutral Link FAULT CURRENT NOTE THAT IF ACTIVE IS SHORTED TO EARTH, ALL EARTHS ARE LIVE!!! Load
139. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Main Switch Earth Link Neutral Link FAULT CURRENT NOTE ALSO THAT UNDER NORMAL CONDITIONS EVERYTHING ELSE WILL STILL WORK OK!!! Load
140. Open Circuit MEN Connection MAIN SWITCHBOARD Circuit Protective Devices Neutral Link Sub Mains Sub Mains Neutral Link DISTRIBUTION BOARD 3 Circuit Protective Devices Earthing Bar DISTRIBUTION BOARD 2 Circuit Protective Devices Neutral Link Earthing Bar Main Earthing Conductor Sub Mains Circuit Protective Devices Neutral Link Earthing Bar DISTRIBUTION BOARD 1 Main Switch What happens on Distribution Boards when the MSB MEN link open-circuits ? AS3000 5.6.6b(iv)
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142. MAIN SWITCHBOARD MEN Connection Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link A N LIVEN UP: -Earth stake -Water pipes -Taps -Sink -Cases of appliances Load
143. MAIN SWITCHBOARD Circuit Protective Devices Neutral Link Sub Mains Sub Mains ` Neutral Link DISTRIBUTION BOARD 3 Circuit Protective Devices Earthing Bar DISTRIBUTION BOARD 2 Circuit Protective Devices Neutral Link Earthing Bar Main Earthing Conductor Sub Mains Circuit Protective Devices Neutral Link Earthing Bar DISTRIBUTION BOARD 1 Main Switch What happens on Distribution Boards when Main Active and Main Neutral are swapped? N A
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145. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link OPEN CIRCUIT Neutral Load
146. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link LOAD CURRENT Load
147. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link LOAD CURRENT Load
148. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link Lo load Resistance Hi stake - earth Resistance: 30 - 2k Load Voltages... High Voltage Low Voltage High Voltage on Earth System
149. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link Lo load Resistance Hi stake - earth Resistance: 30 - 2k High Voltage Low Voltage Livens: -Taps, -Sinks -Water pipes -Metal cases of appliances Load Voltages... High Voltage on Earth System
150. Q: What causes “tingles” on taps? MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link All Loads
151. Q: What causes “tingles” on taps? VD N =4V MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link All Loads
152. Q: What causes “tingles” on taps? MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link All Loads 4V 0V
158. General Requirements Clause No. What to look for 2.9.6 No exposed live parts. E.g. no excessive removal of insulation at terminations, terminal covers in place etc. Double insulation maintained where required. E.g. no single insulation in ceiling above light fittings, no more than 100mm single insulation in wall behind accessories, insulating shrouds installed where required. 1.9 All equipment is approved/compliant with Australian Standards and in good condition. E.g. no unsafe/damaged or non-compliant equipment installed.
159. Consumer Mains Clause No. What to look for 3.4.1 Consumers Mains should be able to carry the maximum demand current of the installation with some capacity to spare. As a guide: 16mm2 (or parallel 6mm2) for overhead mains, 10mm2 for underground mains.
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166. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link Light
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168. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link Light Known resistance
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171. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link Light
172. MAIN SWITCHBOARD Circuit Protective Devices Main Switch Consumer Mains Earth Link Neutral Link Light Switched Active
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176. MEN Connection MAIN SWITCHBOARD Circuit Protective Devices Neutral Link Sub Mains Sub Mains ` Neutral Link DISTRIBUTION BOARD 3 Circuit Protective Devices Earthing Bar DISTRIBUTION BOARD 2 Circuit Protective Devices Neutral Link Earthing Bar Sub Mains Circuit Protective Devices Neutral Link Earthing Bar DISTRIBUTION BOARD 1 Main Switch A N Thank You The End
