1. Cable selection project
Factory office installation

2. maximum demand sub- mains cable
Each factory/warehouse consists of the following loads
8- 250W mercury vapour lamps
4-60watt incandescent lamps
3-18watt fluorescent. External
1-500watt sodium vapour lamp. External
6-10A double single phase outlets
3-20A 3 phase outlets
1- 15A three phase storage hot water

3. Office Lighting 8-double 36 watt fluorescent lights Power
8- double10A single phase outlets
1- single 10A single phase outlet

4. Step 1
Divide the installation into circuits and distribute these circuits across the three phases
Calculate the maximum demand of the installation
The maximum demand of the sub- mains is the load on the heaviest loaded phase

5. Arrange into circuits Factory Office Circuit 1 (4-250W) lamps (R )
Circuit 2 (4-250W) lamps (W)
Circuit 3 (4-60watt) + 2 EF 60W (B)
Circuit 4 (3-18watt) F/lamps (W)
Circuit 5 (1x500watt SV lamps) (B)
Circuit 6 (2 double 10A) outlets (R)
Circuit 7 (2 double 10A) outlets (W)
Circuit 8 (2 double 10A) outlets (B)
Circuit 9 (20A 3 phase) outlet
Circuit 10 (20A 3 phase) outlet
Circuit 11(20A 3 phase) outlet
Circuit 12 (15A 3 phase) HWS
Office
Circuit13 (8 double36 watt fluorescent) (B)
Circuit14 (3 double 10A outlets) (R)
Circuit15 (3 double 10A outlets) (W)
Circuit16 (2 double 1 single 10A outlet) (B)

6. MD Sub-mains using table C2
Factory
Circuit no
Load group
Load
calculation R W B 1 A
(4-250W)MV lamps 1.5A each
4 x 1.5 = 6 6 2
(4-250W) MV lamps 1.5A each 3
(4-18W) energy saver A each
2x60w exhaust fans at 0.3A each
0.8 4
(3-18W) fluorescent 0.12A each
0.36 5
1-500w sodium vapour lamps 0.8 pf
2.72
B i
2-10A double 1Phase outlets = 4
14.14 7
2-10A double 1Phase outlets =4 8

7. Maximum demand Sub-mains
Circuit no
Load group
Load
calculation R W B 9
B (iii)
20A three phase outlet
Full load 20 10
75% Full load 15 11 12 G
15A three phase HWS
office 13 A
8-twin 36w fluorescent
6.24 14
B (i)
3-10A double outlets single phase
19.56 16
2-10A double 1-10A single
Outlets single phase
16.3
Maximum D
104.7
105.6

8. Cable size for sub-main to factory/warehouse unit1
The Maximum demand is 106A
Mains
Sub-mains
X90 SDI Cables double insulated buried in separate U/G conduit
Current carrying capacity T7/ mm² = 135A
Voltage drop T41 Vc =1.62mV/Am
So 25mm² X90 SDI Cables in separate conduits will satisfy both current and voltage drop requirements.
Unit 1 has the longest run (38 metres) so 25mm² will satisfy units 2 and 3

9. Installation load The installation consists of the following loads.
Lighting
24 – 250W mercury vapour Lamps
24 – 2x36W Fluorescent Luminaires 0.78A each
12 – 18W fluorescent to replace 60W
8 – 18W Fluorescent
6 – 60W exhaust fans 0.3A each
3 – 500W

10. Installation load Power 42 – double 10A single phase outlets
3 – single 10A single phase outlets
9 – 20A three phase outlets
3 – 3 phase HWS

11. Consumers Mains maximum demand
Load Group
load
Calculation R W B
24 – 250W mercury vapour Lamps (8 per phase)
8 x 1.5 = 12 12
24 – 2x36W Fluorescent Luminaires (8 per phase)
6.24
12 – 18W fluorescent (0.05A) to replace 60W
4 x 0.05 = 0.2
0.2
6 – 60W exhaust fans (0.3A each)
2 x 0.3 = 0.6
0.6
8 – 18W Fluorescent (0.12A)
3,3,2 per phase
0.12 x 3 =.36
0.12 x 2 = .24
0.36
0.24
3 – 500W
2.71
14 Double +1 single 10A single
outlets per phase (29 per phase)
87 outlets total
95.65
9 – 20A three phase outlets
x 15 =140
140
3 - 15A 3phase HWS
3 x 15 = 45 45 MD
302.8
302.7

12. Cable Size consumers mains
The consumer mains are X90 SDI cables installed in conduit U/G for a length of 40 metres
Determine the cable size to suit current and voltage drop requirements
Table 2.4 item 2 refers to Table 7/16
150mm² = 330A The cable can carry the MD current
Check for voltage drop Table 41 Vc for 150mm² conductors = 0.309mV/Am (60ºC) The cable is rated at 90ºC and by choosing a Vc value at 60ºC this allows for temperature rise under Short circuit conditions

13. Progressive Voltage drop
Consumers main Volt drop volts
10 metres DB
unit3
40 metres
MSB
Turret
20 metres DB
Unit 2
38 metres DB
Unit 1
Sub-main voltage drop 6.52 volts
3.745 Volts
6.52 Volts

14. Progressive Voltage drop distribution board unit 1
Consumers mains
Final sub-circuits
Sub-main
5.57 volts allowed in all single phase circuits Volts allowed in all 3 phase circuits
3.745 volts
3 phase Value
6.52 volts
3 phase value
= volts 3 phase Therefore the 3 phase voltage drop allowed in all 3 phase circuits supplied from the DB Unit1 is 20 – = V
To determine the single phase voltage allowed in final sub circuits
Therefore the single phase Voltage drop allowed in all single phase circuits supplied from distribution board Unit 1 is 11.5 – 5.93 = 5.57 Volts

16. Circuit arrangements Cable Designation Maximum demand
Installation Parameters
AZ/NZS 3008/1/1
Table No
column
Consumers mains
302 A
XLPE (X90)
SDI enclosed UG
Table 2.4
Table 7 4 16
Sub-mains
106 A
X90 SDI enclosed U/G 18
4x250W MV
Lamp Factory
2 circuits 6A
TPS V90 installed with 3 other circuits
De rate 0.78
Table 2.1
Table 9
Table 24 2 8
10A outlets
Factory
16A
TPS V90 installed with 3 other circuits spaced
De rate 0.87 item22

17. Cable designation Maximum demand Installation parameters AS/NZS 3008
Table no
Column no
3 phase outlets
20A
TPS V90 installed with 2 other circuits
On cable
De rate 0.82
Table 2.1
Table 12
Table 24 4 2 8
EF + Battens
In Toilets
0.8A
TPS unenclosed
3 other circuits on cable tray up wall from switchboard
Table 9
De-rate 0.88
HWS 15
3 other circuits on cable tray up wall with 3 other circuits
500W SV
2.8A
TPS installed enclosed U/G
Table 2.4 16

18. Cable Size 20A 3Ø outlets Distribution board Unit 1
Sub-main
Mains
MSB
Unit 1 DB
U/G
turret
Determine the cable size for the 20A 3 phase outlets 1 per circuit, longest run 38 metres The cable is 3core TPS V 90 installed enclosed in air. No de-rating for this section. Unenclosed in air spaced on perforated tray up wall above switchboard 4 circuits
20A
3Ø outlet
To satisfy voltage drop requirements Table 42 a 4 mm² Cable with a Vc value of 9.71 mV/Am value is required

19. Cable Size 20A 3Ø outlets Distribution board Unit 1
Sub-main
Mains
MSB
Unit 1 DB
U/G
turret
Determine the cable size for the 20A 3 phase outlets 1 per circuit,
Route length 25 metres
Current carrying capacity is the limiting factor in this circuit
20A
3Ø outlet
To satisfy Current carrying capacity, a 4mm² TPS cable is required

20. Cable Size 20A 3Ø outlets Sub-main Mains Unit 1 MSB U/G DB turret
Determine the cable size for the 20A 3 phase outlets 1 per circuit,
Route length 15 metres
20A
3Ø outlet
In this instance Voltage drop is not the governing factor. A 4mm² cable is required for CCC

21. 10A single phase outlets
6 outlets in warehouse 2 per phase, (3 circuits).
Circuit 1 (38m route length) The outlet is at the end of the run therefore use MD =10A
Therefore from Table 42, 4mm² cable is required for volt drop
Cable enclosed in conduit on wall with 3 0ther circuits spaced
( 4 circuits )
Table 9/6 4mm² cable = 26A
De-rating Table 22 (0.9) 26 x 0.87 = 23.4A

22. 10A single phase socket outlets
Circuit 2 (30m route length)
Therefore from Table mm² with a Vc value of 15.6mV/A.m is required
Circuit 3 route length 20m route length can also be wired in 2.5mm²
Table 9 column 6 (2.5mm² cable)=20Ax0.9 =18A
So a 2.5mm² cable will satisfy both CCC and Vd

23. Light Circuits unit 1 Circuit 1 (4x250W mercury vapour)
Route length 38m Maximum Demand 4 x 1.5A = 6A.
Circuit beaker rating 10A . Determine Cable size
So from Table 42 a 2.5mm² cable with a Vc value of 15.6mV/A.m three phase 15.6 x =18mV/A.m is required

24. Light Circuits unit 1 Circuit 2 (4x250W mercury vapour)
Route length 44m Maximum Demand 4 x 1.5A = 6A. See clause % of circuit protective device can be used
Circuit beaker rating 10A . Determine Cable size
So from Table 42 a 2.5mm² cable with a Vc value of 15.6mV/A.m three phase 15.6 x =18mV/A.m is required

25. Circuit 3 four battens and 2 EF Toilets
Route length 28m
So from Table mm² cable is required
Table 9 column 6 (1.5mm² cable = 14A)

26. Circuit 4 (3x 18W) Fluorescent
Route length 50m
Voltage drop is not a factor for this circuit
Either 1mm² or 1.5mm² can be used

27. Circuit 5 (500W) sodium Vapour
Route length 16m
TPS Cable V90 Installed enclosed U/G
Distribution
Board
500W Sodium vapour
Voltage drop is not a factor for this circuit
Either 1mm² or 1.5mm² can be used

28. Hot Water Cylinder 3 phase 15A
Route length 28m
Cable 3core + E enclosed TPS V90
Table 12 column 2 (2.5mm² = 23A)
Check Voltage drop
Table 41 (2.5mm² = 15.6mm²)Therefore 2.5mm² Cable

29. Office 8-2x36W(0.78A) fluorescent one circuit
Route length 40m Use 10A MCB
Rule % circuit protective device for voltage drop
Table mm² = 28.6mV/Am.
Use 1.5mm² cable

30. Office10A socket outlets
Circuit 14 (three double outlets)
Route length 22m TPS cable installed unenclosed in air Table 9 column 4 (2.5mm² = 26A)Use 20MCB
Rule (50.% circuit protective device for voltage drop)
Table 42
2.5mm² = 15.6mV/Am
2.5mm Cable for all socket outlet circuits in the office.

31. Fault loop impedance
The earth fault-loop impedance in an MEN system comprises the following parts, starting and ending at the point of the fault.
a) The protective earthing conductor, (PE), including the main earthing terminal/connection or bar and MEN.
b) The neutral return path, consisting of the neutral conductor, (N), between the main neutral terminal or bar and the point at the transformer (the earth return path RG to RB has a relatively high resistance and may be ignored for an individual installation in an MEN system)

32. Fault loop impedance
c) The path through the neutral point of the transformer and the transformer winding.
d) The active conductors as far as the point of the fault.
The earth fault-loop is normally regarded as consisting of the following two parts-
i) conductors upstream or external to the reference point; and
ii) conductors down stream or internal to the reference point.
Refer to appendix B for detail

33. Path taken by an earth fault current

34. Earth fault-loop impedance
Fault current IA
Distributor's network A H
POS
MEN
NeutralBar
Main Earth
Faulty equipment
Soil resistance high between electrodes

35. Determine maximum route length to satisfy fault loop impedance.
The maximum length of a circuit can be determined using Table B1
(Exceptions include circuits wired in 4mm² cable protected by a 16A or 20A Type C MCB)
The maximum length for this example will need to be calculated

36. Calculation 16A MCB
A 4mm² Cable protected by a 16A MCB can be run 109m and not exceed the earth fault loop impedance requirements

37. Switchboards Units 1-3 120A Main switch MCB’S L L L L L P P P P P P HW

38. Main Switch Board