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**About the book:**

Publisher: IET

Place of Publication: United Kingdom

Pages: 217

Edition: 2022

Language: English

Size: 105 Mb

Fully complying with BS7671:201 8+A2:2022.

The Guide provides step-by-step guidance on the design of electrical installations, from domestic installation final circuit design through to complex installations considering fault level calculations for large LV systems.

Apprentices and trainees will also find it very helpful in carrying out calculations necessary for small to medium sized installations.**Content:**

Cooperating organizations 9

Preface 10

Section 1 Design sequence 11

1.1 Load characteristics 11

1.1.1 Load and location (Section 3) 11

1.1.2 Standby systems 12

1.2 Supply characteristics 12

1.3 Installation outline 12

1.4 Distribution design 12

1.4.1 Protective devices and cables (Section 4) 12

1.4.2 Voltage drop (Section 5) 12

1.4.3 Prospective fault currents (Section 6) 12

1.4.4 Shock protection (Section 7) 13

1.4.5 Selection of protective conductors (Section 8) 13

1.4.6 Special installations or locations 13

1.5 Standard final circuits 13

1.6 Isolation and switching 13

1.7 Final assessment 13

1.8 BS7671 13

1.8.1 Departures 13

Section 2 Simple installations and final circuits 15

2.1 Introduction 15

2.2 Supply characteristics 15

2.2.1 General 15

2.2.2 Earthing arrangements 16

2.2.3 Declared supply characteristics 17

2.3 Fault rating of switchgear 18

2.4 Final circuit overcurrent protective devices and cables 18

2.4.1 Radial final circuits 19

2.4.2 Circuits without overload protection 20

2.4.3 Circuits with overload protection 20

2.4.4 30 and 32 A ring final circuits 22

2.5 Final circuit voltage drop limitations 22

2.5.1 Maximum cable length (Lvd) to meet voltage drop limits (i.e. 5 % of 230 V= 11.5 V, or 3 % for lighting = 6.9 V to comply with Regulation 525.202 of BS 7671) 22

2.5.2 Radial final circuit voltage drop 23

2.5.3 Ring final circuit voltage drop 24

2.6 Fault protection 25

2.6.1 Example 1: radial final circuit 26

2.6.2 Example 2: ring final circuit 26

2.7 Short-circuit current protection 27

2.8 Protective conductors T1

2.9 Standard final circuits 28

Section 3 Maximum demand and diversity 29

3.1 Introduction 29

3.2 Installation outline 31

3.3 Final circuit current demand 32

3.3.1 Examples of circuit current demand 33

3.4 Diversity between final circuits 34

3.4.1 Simple installations 34

3.5 Complex installations 38

3.5.1 Accuracy 38

3.5.2 Estimation method 38

Section 4 Selection of cables for current-carrying capacity 4 5

4.0 Symbols 45

4.1 Preliminary design 45

4.2 Overcurrent requirements 46

4.2.1 Fault currents 46

4.2.2 Overload currents 46

4.2.3 Small overloads 47

4.3 Current-carrying capacity tables 48

4.3.1 Tabulated current-carrying capacity lt 48

4.3.2 Ambient temperature rating factor Ca 50

4.3.3 Group rating factor Cg 51

4.3.4 Thermal insulation factor Q 55

4.3.5 Overcurrent protective device and buried circuit rating factors Cf, Cc, Cs and Cd 56

4.3.6 Conductor operating temperature 57

4.4 Protection against overload and short circuit 57

4.4.1 General 57

4.4.2 Overcurrent protection of conductors in parallel 58

4.5 Protection against fault current only (omission of overload protection) 59

4.5.1 Example 59

4.6 Corrections for grouping not liable to simultaneous overload 61

4.6.1 Example 61

4.7 Motors 62

4.7.1 Example 1 62

4.7.2 Example 2 63

4.7.3 Example 3 64

Section 5 Voltage drop 67

5.1 Voltage drop in consumers' installations 67

5.2 Distribution system voltage drop 67

5.3 Basic voltage drop calculation 68

5.3.1 Single-phase 68

5.3.2 Three-phase voltage drop 69

5.3.3 Summing voltage drop 70

5.4 Correction for inductance 70

5.4.1 Example 71

5.5 Correction for load power factor 72

5.5.1 Example 72

5.6 Correction for conductor operating temperature 73

5.6.1 Example 74

5.7 Correction for both conductor operating temperature and load power factor 74

Section 6 Calculation of fault current 7 5

6.1 Determination of prospective fault current 75

6.2 Determined by enquiry 77

6.2.1 General 7 7

6.2.2 Enquiry - maximum prospective short-circuit current, single-phase supplies up to 100 A 77

6.2.3 Enquiry - maximum prospective fault current, three-phase supplies 78

6.2.4 Enquiry - maximum earth fault loop impedances 79

6.3 Determined by calculation 79

6.3.1 Voltage range 79

6.3.2 Calculation - maximum prospective fault current lpf 80

6.3.3 Calculation - minimum prospective fault current lef 82

6.3.4 Example calculations 82

Section 7 Shock protection 87

7.1 Shock protection 87

7.1.1 Introduction 87

7.1.2 Protective measures 87

7.2 Protective measure: automatic disconnection of supply 88

7.2.1 Maximum disconnection times 88

7.2.2 Current causing automatic operation of protective device within the required time (la) 89

7.2.3 Maximum earth fault loop impedance (Z41) 89

7.1 Circuit calculations 92

7.3.1 Example 93

Section 8 Protection against fault current 9 5

8.1 The adiabatic equation 95

8.1.1 Introduction to the adiabatic approach 95

8.1.2 Protection by one device 96

8.1.3 Fault current protection 96

8.1.4 Selection or calculation 96

8.2 Selection from Table 54.7 97

8.2.1 Protective conductors of same material as the line and neutral conductors 97

8.2.2 Protective conductors of a different material to the line and neutral conductors 97

8.3 Introduction to calculations 99

8.3.1 Protective conductors are required to carry leakage currents and earth fault currents 99

8.4 Simple calculation 99

8.4.1 Zs known 100

8.4.2 Circuit-breakers 101

8.5 Energy let-through calculation 102

8.5.1 Circuit-breakers other than those to BS EN 60898 or BS EN 61009 102

8.5.2 Example 103

8.5.3 Types B, C and D circuit-breakers and residual-current circuit-breakers (with overcurrent protection) 103

8.6 Plotting protective conductor adiabatics 106

8.7 Protective conductor as a sheath or armour of a cable 111

8.8 Plotting of cable armour adiabatics 112

8.9 Calculation of armour capability 114

8.9.1 Example using fuse characteristics 115

8.10 Conduit and trunking 118

8.10.1 Example 118

8.10.2 Common protective conductors 118

8.11 Where residual current devices (RCDs) are used for automatic disconnection of supply 119

8.12 Earthing and bonding conductors 120

8.12.1 Earthing conductor 120

8.12.2 Main protective bonding conductors 122

8.12.3 Supplementary bonding conductors 122

Section 9 Calculations associated with testing 127

9.1 General 127

9.2 Continuity 128

9.2.1 Example 128

9.3 Continuity of ring final circuit conductors 129

9.3.1 Introduction 129

9.3.2 Calculation of the expected measured reading between line and protective earth (PE) at a point on the ring 129

9.3.3 Calculation of the minimum reading as a percentage of maximum reading and percentage deviation 131

9.3.4 Example 131

9.4 Earth fault loop impedance Zs 133

9.4.1 BS 7671 earth fault loop impedance tables 133

9.4.2 Earth fault loop impedance corrections for temperature 133

9.5 Reduced cross-sectional area protective conductors 135

Section 10 Impedance of copper and aluminium conductors 137

10.1 Introduction 137

10.2 Conductor resistance and temperature 137

10.2.1 Example 138

10.3 Impedance of cables from voltage drop tables 138

10.3.1 Single-phase 138

10.3.2 Three-phase 139

Section 11 Harmonics 143

11.1 Introduction 143

11.2 Cable ratings 144

11.2.1 Example 1 145

11.2.2 Example 2 145

11.3 Voltage drop 145

11.3.1 Cable sizes larger than 16 mm2 146

11.3.2 Cable sizes 16 m m2 and smaller 146

11.3.3 Examples with cable size over 16 mm2 146

11.4 Overcurrent protection 147

11.4.1 Example 148

Section 12 Protection against voltage disturbances 149

12.1 Introduction 149

12.2 Overvoltages 149

12.3 Power frequency fault voltages 149

12.4 Power frequency stress voltages 153

12.5 Earthing of 11 kV substations 153

Section 13 Busbar trunking 155

13.1 Symbols 155

13.2 Voltage drop 155

13.2.1 Example 1 155

13.2.2 Example 2 155

13.3 Fault currents 156

13.3.1 Example 157

Section 14 Prosumer's electrical installations (PEIs) 159

14.1 Introduction to prosumer's electrical installations (PEIs) 159

14.2 Supply characteristics of PEIsin different operating modes 160

14.2.1 Connected mode 160

14.2.2 Island mode 161

14.3 Overcurrent protection and connection of generators 161

Appendix A Symbols 163

Appendix B Standard final circuits 167

Appendix C Avoidance of unintentional operation of circuit-breakers 177

C1 Lighting circuit applications 178

C1-1 Example 179

Appendix D Further cable calculations 181

D1 Cable life 181

D1-1 British Cables Association 181

D2 Temperatures (core and sheath) (Effect of load current on conductor operating temperature) 182

D3 Inductance of cables in parallel 182

D4 Calculation of sheath voltages 183

D4-1 Example 184

D5 Earth fault loop impedance calculations for cables according to NA.4 of

National Annex NA to PD CLC/TR 50480:2011 1 84

D5-1 Introduction 184

D5-2 Cables in steel conduit where the conduit is used as the circuit protective conductor (NA.4.2 of PD CLC/TR 50480) 185

D5-3 Cables in steel trunking where the trunking is used as the circuit protective conductor (NA.4.3 of PD CLC/TR 50480) 186

D5-4 Steel wire armoured multicore cables where the armour is used

as the circuit protective conductor (NA.4.4 of PD CLC/TR 50480) 186

D5-5 External circuit protective conductor in parallel with steel wire armoured multicore cable (NA.4.5 of PD/CLC-TR 50480) 186

D5-6 Aluminium armoured single-core cables where the armour is used as the circuit protective conductor (NA.4.6 of PD/CLC-TR 50480) 187

Appendix E Symbols from PD CLC/TR 50480:2011 189

Appendix F Equipment data 191

Index 207