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Electrical Thumb Rules

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Size of Cable on Secondary Side of Transformer (11KV/433V)
Ref: KSEI Handbook
Rating of T/C (KVA) Primary current (Amp) Secondary Current (Amp) Min. Size of Neutral Earthing Conductor (mm2) Minimum Size of Cable (mm2)
63 3.3 84 25X3 50mm2
100 5.25 133.3 25X3 95mm2 or (2×50 mm2)
160 8.4 213.3 25X3 185mm2 or (2×95 mm2)
200 10.49 266.6 25X3 300mm2 or (2×120 mm2)
250 13.12 333 25X3 2×185 mm2
315 16.53 420 31X3 or 25X4 (2×300 mm2) or (3×185 mm2)
400 21.80 533 38X3 (3×300 mm2) or (2×400 mm2)
500 26.20 666.5 25X6 (3×400 mm2) or (4×240 mm2)
630 33 840 31X6 4×400 mm2
750 39.36 1000 50X4 Bus Bar Trucking (min. Isc 50KA)
1000 52.50 1333 210mm2 Bus Bar Trucking (min. Isc 50KA)
1250 65.50 1667 290mm2 Bus Bar Trucking (min. Isc 50KA)
1600 83.98 2133 380mm2 Bus Bar Trucking (min. Isc 50KA)
2000 105.00 2666 450mm2 Bus Bar Trucking (min. Isc 50KA)

 

HT Fuse on Primary Side of Transformer (11KV/433V)
Rating of T/C (KVA) Primary current (Amp) Secondary Current (Amp) HT Fuse
Min (Amp) Max(Amp)
63 3.3 84 10 16
100 5.25 133.3 16 25
160 8.4 213.3 16 40
200 10.49 266.6 25 40
250 13.12 333 32 40
315 16.53 420 40 63
400 21.80 533 40 63
500 26.20 666.5 50 100
630 33 840 63 100
750 39.36 1000 75 160
1000 52.50 1333 100 160
1250 65.50 1667 100 200
1600 83.98 2133 160 250
2000 105.00 2666 200 250

Capacitor Bank for Power Supply Voltage
System Voltage Minimum rating of capacitor bank
3.3 KV , 6.6KV 75 Kvar
11 KV 200 Kvar
22 KV 400 Kvar
33 KV 600 Kvar

Capacities of PVC conduits
Nominal conductor Size mm 16 mm 20 mm 25 mm 32 mm
Number of Cables (maximum)
1.0 6 5 19 30
1.5 5 4 15 24
2.5 3 3 11 17
4 2 2 8 13
6 2 - 6 10
10 - - 4 6
16 - - 3 4
25 - - 2 3
35 - - - 2

System Highest and Lower Voltage
Ref: NEC(India) :2011
System Voltage Highest Voltage Lowest Voltage
240 V 264 V 216 V
415 V 457 V 374 V
3.3 kV 3.6 kV 3.0 kV
6.6 kV 7.2 kV 6.0 kV
11 kV 12 kV 10 kV
22 kV 24 kV 20 kV
33 kV 36 kV 30 kV
66 kV 72.5 kV 60 kV
66 kV 72.5 kV 60 kV
132 kV 145 kV 120 kV
220 kV 245 kV 200 kV
400 kV 420 kV 380 kV

Number of Points for Dwelling Unit
Ref: NEC(India) :2011
No. Description Area for the Main Dwelling Unit (m2)
35 mm2 45 mm2 55 mm2 85 mm2 140 mm2
1 Light points 7 No 8 No 10 No 12 No 17 No
2 Ceiling fans Pont 2 No 3 No 4 No 5 No 7 No
3 Ceiling fans No’s 2 No 2 No 3 No 4 No 5 No
4 6A Socket outlets 2 No 3 No 4No 5 No 7 No
5 16A Socket outlets - 1 No 2 No 3 No 4No
6 Call-bell (buzzer) - - 1 No 1 No 1 No

Recommended Schedule of Socket-Outlets
Ref: NEC(India) :2011
Description Number of Socket
6A Socket 16A Socket
Bedroom 2 1
Living room 2 2
Kitchen 1 2
Dining room 2 1
Garage 1 1
For refrigerator - 1
For air-conditioner - 1 for each
Verandah 1 per 10mter2 1
Bathroom 1 1

Power requirements of the building
Ref: NEC(India) :2011
Part of ElectricalInstallation Part of the Total Power Requirement in % DiversityFactor
Ventilation, heating (air-conditioning) 45% 1.0
Power plant (drives) 52% 0.65
Lighting 30% 0.95
Lifts 20% 1.0
Kitchen 10% 0.6
Laundry 5% 0.6

Lift Car Speed
Ref: NEC(India) :2011
Occupancy No. of Floors Served Car Speed   m/s
Office building 4 to 5 0.5 to 0.75 m/sec
Office building 6 to 12 0.75 to 1.5 m/sec
Shops and departmental stores 13 to 20 More than 1.5 m/sec
Passenger lifts for low and medium lodging houses - 0.5 m/sec
Hotels 4 to 5 0.5 to 0.75 m/sec
Normal load carrying lifts - 2.0 to 2.5 m/sec
Hospital passenger Lift 4 to 5 0.5 to 0.75 m/sec
Hospital passenger Lift 13 to 20 More than 1.5 m/sec
Hospital bed lifts (Short travel lifts insmall hospitals) - 0.25 m/sec
Hospital bed lifts (Normal) - 0.5 m/sec
Hospital bed lifts (Long travel lifts inGeneral hospitals) 0.6 to 1.5 m/sec

Capacitor Ratings at Rated Voltage
Ref: NEC(India) :2011
Motor Rating(Kw) Capacitor Rating in kVAR for Motor Speed
3 000rev/min 1 500rev/min 1 000rev/min 750rev/min 600rev/min 500rev/min
2.25 1 1 1.5 2 2.5 2.5
3.7 2 2 2.5 3.5 4 4
5.7 2 3 3.5 4.5 5 5.5
7.5 3 4 4.5 5.5 6 6.5
11.2 4 5 6 7.5 8.5 9
15 5 6 7 9 11 12
18.7 6 7 9 10.5 13 14.5
22.5 7 8 10 12 15 17
37 11 12.5 16 18 23 25
57 16 17 21 23 29 32
75 21 23 26 28 35 40
102 31 33 36 38 45 55
150 40 42 45 47 60 67
187 46 50 53 55 68 76

:Maximum Current Demand for Motor:
Ref: NEC(India) :2011
Nature of supply Size of installation Maximum current demand
Single phaseor Three phase Up to and including 0.75 kW Six times the full load current
Above 0.75 kW and up to 7.5 kW Three times the full load current
Above 7.5 kW up to and up to11 kW Two times the full load current
Above 11 kW One and half times the full load current

Rated Basic Insulation Level (BIL)
Ref: NEC(India) :2011
Nominal System Voltage (kV) Rated BIL (kVp)
33 KV 170
22 KV 125
11 KV 75
6.6 KV 60
3.3 KV 40

Illumination Level
Ref: NEC(India) :2011
Location Illumination Level (Lux)
Residence
Entrance / Hallways 100
Living room 300
Dining Room 150
Bed Room (General) 300
Bed Room (Dressing , Bed Heads) 200
Kitchen 200
Kitchen sink 300
Bathroom 100
Sewing 700
Workshop 200
Staircase 100
Garage 70
Study Room 300
Office Building
Entrance hall / Reception 150
Conference Room / Executive Office 300
General Office Space 300
Business Machinery Operation 450
Drawing Office 450
Corridors 70
Stairs 100
Lift landing 150
Hospital Building
Reception & Waiting 150
General ward 100
Bed Side 150
Toilet 70
Stairs 100
Operation Theatre (General) 300
Operation Theatre (Operation Table) Special
Laboratories 300
Radiology 100
Causality 150
Dispensaries 300
Laundry 200
Dry Cleaning 200
Ironing 300
General Office 450
Kitchen 200
Assembly & Concert Halls
Foyers 100 to 150
Auditoria 100 to 150
Platform 450
Corridors 70
Stairs 100
Cinema Halls
Foyers 150
Auditoria 50
Corridors 70
Stairs 100
Theatres
Foyers 150
Auditoria 70
Corridors 70
Stairs 100
School / College Building
Assembly Halls
General 150
Examination center 300
Platform 300
Classes
Desktop 300
Blackboard 200 to 300
Libraries
Shelves 70 to 150
Reading Room 150 to 300
Reading Table 300 to 700
Cataloguing 150 to 300
General
Office 300
Staff Room 150
Corridors 70
Stairs 100

Lamp’s Lumen Data
Rating (Watt) Life (Hours) Initial Lumens
Incandescent Lamp
60 1000 870
100 750 1750
150 2000 1740
200 2000 2300
500 2000 6500
Fluorescent Lamp
18 7000 1120
20 7000 1020
36 7000 2800
40 7000 2700
2X40 7000 4000
Compact Fluorescent Lamp
5 10000 220
7 7000 380
11 7000 560
13 7000 680
15 7000 810
18 7000 1050
23 7000 1500
26 7000 1800
32 7000 2400
Mercury Vapour Lamp
100 18000 3700
175 24000 8600
250 24000 12100
400 24000 22500
1000 24000 57000
Metal Halide Lamp
50 15000 3400
70 15000 5600
100 15000 9000
150 10000 13500
175 10000 15000
250 10000 20500
400 20000 36000
1000 12000 110000
High Pressure Sodium Vapour Lamps
35 16000 2250
50 24000 4000
70 24000 5800
100 24000 9500
150 24000 16000
250 24000 27500
400 24000 47500
1000 24000 140000
Pulse Start Metal Halide Lamp
50 15000 3400
70 15000 5600
100 15000 9000
150 15000 15000
175 15000 17500
200 15000 21000
250 15000 26300
320 20000 34000
400 20000 44000
450 20000 50000

:Duty Type of Motor:
Ref: IS-325
Duty Type Symbol Duty Type Application
S1 Continuous Duty Pumps, Bowers, Compressors, Fans
S2 Short Time Duty Siren, Flood relief Gates
S3 Intermittent Periodic Duty Valve, Actuators, Wire drawing machine
S4 Intermittent Periodic Duty with starting Hoist, Cranes, Lifts, Escalators
S5 Intermittent Periodic Duty with starting / Breaking Hoist, Cranes (with electronics Breaks), Rolling mills
S6 Continuous Duty with Intermittent Periodic Duty Machine tools, Conveyors
S7 Continuous Duty with starting / Breaking Machine tools,
S8 Continuous Duty with periodic load changes Pole Channing Applications

Type of Distribution System
As per IEC 60364-3
Unearthed System Earthed System
IT TT / TN (TN-S,TN-C,TN-C-S)
First Letter (the neutral point in relation to earth):T= directly earthed neutral (from the French word Terre)I =unearthed or high impedance-earthed neutral (e.g. 2,000 Ω)
Second letter (Exposed conductive parts of the electrical installation in relation to earth):T =directly earthed exposed conductive partsN =exposed conductive parts directly connected to the neutral conductor

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Credits: Mr. Jignesh Parmar
About Jignesh Parmar 

Jignesh Parmar has completed his B.E(Electrical) from Gujarat University. He is member of Institution of Engineers (MIE),India. Membership No:M-1473586.He has more than 12 years experience in Transmission -Distribution-Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-Designing-Technical Review-coordination -Execution). He is Presently associate with one of the leading business group as a Assistant Manager at Ahmedabad,India. He has published numbers of Technical Articles in "Electrical Mirror", "Electrical India", "Lighting India", "Industrial Electrix"(Australian Power Publications) Magazines. He is Freelancer Programmer of Advance Excel and design useful Excel base Electrical Programs as per IS, NEC, IEC,IEEE codes. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & Knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

Last Updated on Wednesday, 20 August 2014 13:46