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**Cable selection project**

Factory office installation

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**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

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**Office Lighting 8-double 36 watt fluorescent lights Power**

8- double10A single phase outlets 1- single 10A single phase outlet

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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

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**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)

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**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

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**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

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**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

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**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

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**Installation load Power 42 – double 10A single phase outlets**

3 – single 10A single phase outlets 9 – 20A three phase outlets 3 – 3 phase HWS

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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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

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**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

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**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

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**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

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**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)

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**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

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**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

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**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

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**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

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**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.

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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)

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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

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**Path taken by an earth fault current**

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**Earth fault-loop impedance**

Fault current IA Distributor's network A H POS MEN NeutralBar Main Earth Faulty equipment Soil resistance high between electrodes

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**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

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

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

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Main Switch Board

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