10/17/2014
Electrical Thumb Rules You MUST Follow (Part 1) | EEP
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Electrical Thumb Electrical Thumb Rules You MUST Follow (Par t 1) Electrical Electrical Thumb R ules ules You MUST Fo Follow (Part 1)
Electrical Thumb Rules For: Cable Capacity Cable Current Capacity of Equipment Earthing Ear thing Resistance Resistance Minimum Bending Radius Insulation Resistance Lighting Arrestor Transformer Trans former Diesel Generator Current Transformer Quick Electrical Calculation
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Electrical Thumb Rules You MUST Follow (Part 1) | EEP
Cable Capacity
6X Size of Wire in Sq.mm Ex. For 2.5 Sq.mm = 6×2.5 = 15 Amp, For 1 Sq.mm = 6×1 = 6 Amp, For 1.5 Sq.mm = 6×1.5 = 9 Amp For Cable Current Capacity = 4X Size of Cable in Sq.mm, Ex. For 2.5 Sq.mm = 4×2.5 = 9 Amp. Nomenclature for cable Rating = Uo/U where Uo = Phase-Ground Phase- Ground Voltage, Volt age, U = Phase-Phase Phase- Phase Voltage, Volt age, Um = Highest High est Permissibl Permi ssiblee Voltage Volt age For Cu Wire Current Capacity (Up to 30 Sq.mm) =
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Current Capacity of Equipment 1 Phase Motor draws Current = 7Amp per HP. 3 Phase Motor draws Current = 1.25Amp per HP. Full Load Current of 3 Phase Motor = HPx1.5 Full Load Current of 1 Phase Motor = HPx6 No Load Current of 3 Phase Motor = 30% of FLC KW Rating of Motor = HPx0.75 http://electrical-engineering-portal.com/electrical-thumb-rules-you-must-follow-part-1#1
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Electrical Thumb Rules You MUST Follow (Part 1) | EEP
Full Load Current of equipment = Full Load Current of equipment =
1.39xKVA ( for 3 Phase 415Volt 415Vo lt ) 1.74xKw ( for 3 Phase 415Volt 415Vol t )
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Earthing Resistance Earthing Resistance for Single Pit = 5Ω, Earthing Grid = 0.5Ω As per NEC 1985 198 5 Earthing Eart hing Resist Res istance ance should be < 5Ω. Voltage Volt age betw between een Neutral Neut ral and Earth Eart h <= 2 Volt Resistance between Neutral and Earth <= 1Ω Creepage Distance = 18 to 22mm/KV ( Moderate Moder ate Polluted Pollu ted Air ) or Creepage Distance = 25 to 33mm/KV ( Highly Highly Polluted Air )
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Minimum Bending Radius Minimum Bending Radius for LT Power Cable = 12 x Dia of Cable. Minimum Bending Radius for HT Power Cable = 20 x Dia of Cable. Minimum Bending Radius for Control Cable = 10 x Dia of Cable.
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Insulation Resistance Insulation Resistance Value for Rotating Machine = (KV+1) MΩ. Insulation Resistance Value for Motor (IS 732) = ((20xVoltage (L-L)) / (1000+ (2xKW)). Insulation Resistance Value for Equipment (<1KV) = Minimum 1 MΩ. Insulation Resistance Value for Equipment (>1KV) = KV 1 MΩ per 1KV. Insulation Resistance Value for Panel = 2 x KV rating of the panel. Min Insulation Resistance Value (Domestic) = 50 MΩ / No of Points. ( All Electric Elec trical al Points Point s with Electrical fitting & Plugs ). Should Shoul d be less than 0.5 MΩ Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. ( All Electri Elec trical cal Points without fitting & Plugs ).Should ).Sh ould be less than 0.5 MΩ. Test Tes t Voltage Volt age (A.C) (A.C ) for Meggeri Megg ering ng = (2X Name Plate Voltage) +1000 Test Tes t Voltage Volt age (D.C) (D.C ) for Meggeri Megg ering ng = (2X Name Plate Voltage). Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.
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10/17/2014
Electrical Thumb Rules You MUST Follow (Part 1) | EEP
Lighting Arrestor Arrestor Arre stor have Two Rating: Rati ng:
1. MCOV=Max. Continuous Line to Ground Operating Voltage. 2. Duty Cycle Voltage. ( Duty Duty Cycle Voltage > MCOV ). Go to Content ↑
Transformer Current Rating of Transformer = KVA x 1.4 Short Circuit Current of T.C /Generator = Current Rating / % Impedance No Load Current of Transformer =< 2% of Transformer Rated current Capacitor Current (Ic) = KVAR / 1.732xVolt ( Phase-Phase Phase-Phase ) Typically Typi cally the local utility util ity provides provi des transformer trans formerss rated up to 500kVA For maximum connected load of 99kW, Typically Typi cally the local utility util ity provides provi des transformer trans formerss rated up to 1250kVA For maximum connected load of 150kW. The diversity diver sity they would apply to apartments apart ments is around 60% Maximum HT (11kV) connected load will be around 4.5MVA per circuit. 4No. earth pits per transformer ( 2No. 2No. for body and 2No. for neutral earthing ),
Clearances, approx.1000mm around TC allow for transformer movement for replacement. Go to Content ↑
Diesel Generator Diesel Generator Set Produces = 3.87 Units (KWH) in 1 Litter of Diesel. Requirement Area of Diesel Generator = for 25KW to 48KW = 56 Sq.meter,
100KW = 65
Sq.meter. DG less than or equal to 1000kVA must be in a canopy. DG greater 1000kVA can can either be in a canopy or skid mounted in an acoustically treated room DG noise levels to be less than 75dBA at 1 meter. DG fuel storage tanks should be a maximum of 990 Litter per unit. Storage tanks above this level will trigger more stringent explosion protection provision. Go to Content ↑ http://electrical-engineering-portal.com/electrical-thumb-rules-you-must-follow-part-1#1
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Current Transformer Nomenclature of CT: Ratio: input / output current ratio Burden (VA): total burden including pilot wires. ( 2.5, 2.5, 5, 10, 15 and 30VA. ) ) Class: Accuracy required for operation ( Meterin Met ering: g: 0.2, 0.5, 1 or 3, Protecti Prot ection: on: 5, 10, 15, 20, 30 ). Accurac Acc uracyy Limit Limi t Factor: Fact or: Nomenclature of CT: Ratio, VA Burden, Accuracy Class, Accuracy Limit Factor. Example: 1600/5, 15VA 5P10 ( Ratio: Ratio: 1600/5, Burden: 15VA, Accuracy Class: 5P, ALF: 10 ) As per IEEE Metering Mete ring CT: 0.3B0.1 rated Metering CT is accurate accurate to 0.3 percent if the
connected secondary burden if impedance imped ance does not exceed 0.1 ohms. As per IEEE Relaying Rela ying (Protec (Pro tection tion)) CT: 2.5C100 Relaying CT is accurate within 2.5 percent if the secondary burden is less than 1.0 ohm (100 volts/100A). Go to Content ↑
Quick Electrical Calculation 1HP = 0.746KW
Star Connection
1KW = 1. 36HP
Li ne Vol t age = √3 Phase Vol t age
1W at t = 0. 846 K la/ Hr
L i n e C u rr e n t = P h a s e C u r r e n t
1Watt = 3.41 BTU/Hr
Delta Connection
1KW H = 3. 6 MJ
L in e V olt age = Phase Vo lt age
1C al = 4. 186 J
Li ne Current = √3 Phase Current
1Tone = 3530 BTU 85 Sq.ft Floor Area = 1200 BTU 1Kcal = 4186 Joule 1KWH = 860 Kcal 1Cal = 4.183 Joule Go to Content ↑
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About Author //
Jignesh Jigne sh Parmar jiguparmar - Jignesh Jigne sh
Parmar has completed compl eted his B.E(Elect B.E( Electrical rical)) from Gujarat University. He is member of Institution of Engineers (MIE),India. Membership No:M-1473586.He has more than 12 years experience in Transmissio Transm issionn -Distribut -Dist ribution-E ion-Elect lectrical rical Energy Energ y theft detection detec tion-Elec -Electrica tricall Maintenance-Electrical Projects (Planning-Designing-Technical Reviewcoordination -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 Advan ce Excel and design desig n useful Excel base Electrical Elect rical Programs Progra ms as per IS, NEC, IEC,IEEE IEC,I EEE 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.
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