Electrical Thumb Rules-(Part 1)

Elec Electr tric ical al Thum Thumb b Rul Rules es-( -(Pa Part rt 1). 1). | Elec Electr tric ical al Note Notess & Art Artic icle less

http https: s:// //el elec ectr tric ical alno note tes. s.wo word rdpr pres ess. s.co com/ m/20 2013 13/0 /07/ 7/27 27/e /ele lect ctri rica call-th thum umbb-ru rule less-.. ....

Electrical Notes & Articles Sharing Abstracts,Notes on various Electrical Engineering Topics.

Electrical Thumb Rules-(Part 1). JULY JULY 27, 2013 49 COMMENTS COMMENTS (HTTPS://ELECTRICALNO (HTTPS://ELECTRICALNOTES.WORDPRES TES.WORDPRESS.COM/2013/07/27/E S.COM/2013/07/27/ELECTRICALLECTRICAL-THUMBTHUMBRULES-PART-1-2/#COMMENTS)

Cable Capacity: For Cu Wire Current Capacity (Up to 30 Sq.mm) = 6X Size of Wire Wire in Sq.mm Ex. For 2.5 Sq.mm=6×2.5= Sq.mm=6×2.5=15 15 Amp, For 1 Sq.mm=6×1= Sq.mm=6×1=66 Amp, For 1.5 Sq.mm=6×1. Sq.mm=6×1.5=9 5=9 Amp For Cable Current Capacity = 4X Size of Cable Cable in Sq.mm ,Ex. ,Ex. For 2.5 Sq.mm=4×2.5= Sq.mm=4×2.5=99 Amp. Nomenclature for cable Rating = Uo/U = Uo/U where Uo=Phase-Ground Voltage, U=Phase-Phase Voltage, Um=Highest Permissible Voltage

Current Capacity of Equipments: 1 Phase Motor draws Current=7Amp Current=7Amp per HP. 3 Phase Motor draws Current=1.25Amp Current=1.25Amp per HP. Full Load Current of 3 Phase Motor=HPx1.5 Motor=HPx1.5 Full Load Current of 1 Phase Motor=HPx6 Motor=HPx6 No Load Current of 3 Phase Motor =30% = 30% of FLC KW Rating of Motor=HPx0.75 Motor= HPx0.75 Full Load Current of equipment =1.39xKV = 1.39xKVA A (for 3 Phase 415Volt) Full Load Current of equipment =1.74xKw = 1.74xKw (for 3 Phase 415Volt)

Earthing Resistance: Earthing Resistance for Single Pit=5Ω Pit= 5Ω ,Earthing Grid=0.5Ω As per NEC 1985 Earthing Resistance should Resistance should be <5Ω. Voltage between Neutral and Earth <=2 Earth <=2 Volts Resistance between Neutral and Earth <=1Ω Earth <=1Ω Creepage Distance=18 Distance=18 to 22mm/KV (Moderate Polluted Air) or Creepage Distance=25 Distance=25 to 33mm/KV (Highly Polluted Air)

Minimum Bending Radius: Minimum Bending Radius for LT Power Cable=12xDia Cable= 12xDia of Cable. Minimum Bending Radius for HT Power Cable= 20xDia of Cable. Minimum Bending Radius for Control Cable=10xDia Cable= 10xDia of Cable.

Electrical Thumb Rules-(Part 1). | Electrical Notes & Articles

https://electricalnotes.wordpress.com/2013/07/27/electrical-thumb-rules-...

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 Electrical Points with Electrical fi ing & Plugs).Should

be less than 0.5 MΩ Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. (All Electrical Points without fi ing & Plugs).Should be

less than 0.5 MΩ. Test Voltage (A.C) for Meggering = (2X Name Plate Voltage) +1000 Test Voltage (D.C) for Meggering = ( 2X Name Plate Voltage). Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.

Lighting Arrestor: Arrestor have Two Rating=

(1) MCOV=Max. Continuous Line to Ground Operating Voltage. (2) Duty Cycle Voltage. (Duty Cycle Voltage>MCOV).

Transformer: Current Rating of Transformer =KVAx1.4 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) Typically the local utility provides transformers rated up to 500kVA For maximum connected load of 99kW, Typically the local utility provides transformers rated up to 1250kVA For maximum connected load of 150kW. The diversity they would apply to apartments is around 60% Maximum HT (11kV) connected load will be around 4.5MVA per circuit.

4No. earth pits per transformer (2No. for body and 2No. for neutral earthing), Clearances, approx.1000mm around TC allow for transformer movement for replacement.

Diesel Generator: Diesel Generator Set Produces=3.87 Units (KWH) in 1 Li er 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 either be in a canopy or skid mounted in an acoustically treated room DG noise levels to be less than 75dBA @ 1meter. DG fuel storage tanks should be a maximum of 990 Li er per unit Storage tanks above this level will trigger more stringent

explosion protection provision.

Current Transformer: Nomenclature of CT:



Ratio: input / output current ratio Burden (VA): total burden including pilot wires. (2.5, 5, 1 0, 15 and 30VA.) Class: Accuracy required for operation (Metering: 0.2, 0.5, 1 or 3, Protection: 5, 10, 15, 20, 30) . Accuracy Limit Factor: Nomenclature of CT: Ratio, VA Burden, Accuracy Class, Accuracy Limit Factor. Example: 1600/5, 15VA 5P10 (Ratio: 1600/5,

Burden: 15VA, Accuracy Class: 5P, ALF: 10) As per IEEE Metering CT: 0.3B0.1 rated Metering CT is accurate to 0.3 percent if the connected secondary burden if impedance does not exceed 0.1 ohms. As per IEEE Relaying (Protection) CT: 2.5C100 Relaying CT is accurate within 2.5 percent if the secondary burden is less than 1.0 ohm (100 volts/100A). Quick Electrical Calculation

1HP=0.746KW

Star Connection

1KW=1.36HP

Line Voltage=√3 Phase Voltage

1Wa =0.846 Kla/Hr

Line Current=Phase Current

1Wa =3.41 BTU/Hr

Delta Connection

1KWH=3.6 MJ

Line Voltage=Phase Voltage

1Cal=4.186 J

Line Current=√3 Phase Current

1Tone= 3530 BTU 85 Sq.ft Floor Area=1200 BTU 1Kcal=4186 Joule 1KWH=860 Kcal 1Cal=4.183 Joule

FILED UNDER UNCATEGORIZED About Jignesh.Parmar

Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 13 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for ʺElectrical Mirrorʺ and ʺElectrical Indiaʺ Magazines. 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.

49 Responses to Electrical Thumb Rules-(Part 1). Mohammadasif Thakor says:

July 27, 2013 at 5:56 pm Very useful information Thanks



Reply MASILAMANI.V says:

July 28, 2013 at 2:36 am excellent for this words Reply Dillip Kumar Deo says:

April 16, 2014 at 9:29 am Jignesh it is very usefull for all engineers. Reply Chisi says:

July 28, 2013 at 6:04 am Man, you are the best..I never knew most of these rules. Long live Jignesh! Reply HEENA says:

July 28, 2013 at 8:50 am 3 PHASE MOTOR DRAWS CURRENTS – 2.5 AMP/hp.if it is 230 v and 1.5A/HP If it is 440 volt . Can you also please add formulas too.. Reply Jignesh.Parmar says:

July 28, 2013 at 12:22 pm Read Tile of this Page.This is THUMB RULES so There is no any formula/References/Code For that !!! This is used for Quick calculation… Reply SUBRAMANIAN.P says:

July 28, 2013 at 12:49 pm Really the topics is very useful to me Reply arvind says:

July 28, 2013 at 5:21 pm VERY USEFUL AND HANDY INFO Reply arvind says:

July 28, 2013 at 5:22 pm very imp info Reply [email protected] says:

July 29, 2013 at 4:38 am Dear Jignesh I am regularly ge ing updateds from this websites. It is very useful. Can you please reply me for following query. As per Indian standrad : Emergency standby duty generator ( for example : 1250 KVA,415 V) can be loaded for full load (i.e 1 250 KVAconstant or vairiable load ) in case of main power source outgae for 3 days. If any supporting IS number is available -please advise. In case Alternate relevant international standard is clarifying this query -please advise. With best regards Shailesh G Patel Reply siddu.biradar says:



July 29, 2013 at 4:53 am it is very useful for electrical engineer and thank you very much Mr jignesh Reply Suresh says:

July 29, 2013 at 2:52 pm Very useful in short. Thanks Reply boy sandra says:

August 2, 2013 at 7:00 pm great refferences, i joined your page on facebook and followed your blog by email Reply Praveen Malviya says:

August 3, 2013 at 11:37 am Sir please help me… My question is, what is the suitable stater and breaker for 400kw,1440rpm induction motor… Reply engelect says:

August 3, 2013 at 10:44 pm Thanks for this rule of thumbs. It is really usefull for short assesment. Reply Murali.k says:

August 4, 2013 at 2:01 am Thanks yery useful for all electrical engineers in the world Reply malebogo moupi says:

August 4, 2013 at 7:17 am hie sir help me here’a single phase load consists of 1. 12kw of lighting & heating at unity pf.2. 8kw of motors at 0.8pf lagging & 3. 10kva of motors at 0.7 pf lagging.calculate (a)kwt (b)kvart (c)kvat (d)overall pf and the total supply current at 240v.my main wory is how to come with 30.3total kva.13.1total kvar &overall pf pliz help! Reply vamsi says:

August 7, 2013 at 3:35 pm as a site engineer this info is very helpfull to me .. Reply Rasika says:

August 13, 2013 at 5:02 am what are electrodynamic stresses? Reply pankaj says:

August 20, 2013 at 11:21 am yes Reply Almoutaz Safwan says:

September 2, 2013 at 11:41 am It’s useful info. thanks Reply Dharmendra Kumar says:

September 29, 2013 at 11:26 am THIS INFORMATION IS VERY USEFUL FOR EVERY ENGINEER AND ELECTRICAL MAINT. PERSON. THANKS JIGNESH. _ DHARMENDRA KUMAR Reply jayesh says:

September 29, 2013 at 11:33 am so greatful job you had done.



Jay jay garvi gujarat Reply chandresh says:

October 8, 2013 at 5:25 am thank u sir……………………………. Reply Nilesh Prajapati says:

October 13, 2013 at 5:06 am Thank you sir Reply Steve says:

October 23, 2013 at 5:34 pm thank you for all your hard work in pu ing this together….Greetings from West Texas Reply surender says:

October 26, 2013 at 8:02 am in what case voltage reading between ground and neutral up to 230 at distribution transformer L T side .The transformer ratio is 33 kv / .415 kv . Reply Jignesh.Parmar says:

October 26, 2013 at 6:06 pm Already given in the Blog !!!!! (< 5V) Reply Ravindra Kumar says:

November 10, 2013 at 10:51 pm thank you very much sir……… Reply yadvendra sharma says:

November 15, 2013 at 12:46 pm All the three phase are generate in the power plant…Sir plz t ell me about the neutral generation… Plz reply soon. Reply Sumit Sharma says:

November 23, 2013 at 11:06 am Dear Sir i am working in residential building my one flat load is 15 kw so how to calculate diversity factor. regards Sumit Sharma Reply Bhavin Patel says:

December 18, 2013 at 3:35 am sir thanks for sharing such a information Reply K.Gopinath says:

January 3, 2014 at 7:38 am Thank you sir, i am never know about this thumb rules. Reply Alwin Paul says:

January 23, 2014 at 2:29 pm Dear Mr. Jignesh ■1 Phase Motor draws Current=7Amp per HP.



■3 Phase Motor draws Current=1.25Amp per HP

Can you explain the above information, please? Reply Jignesh.Parmar says:

January 23, 2014 at 4:56 pm Dear Alwin.. This is “THUMB RULE”..This is Quick and handy calculation which is near to mathematical calculation or it’s equation. Reply Paramasivan Tsp says:

January 27, 2014 at 6:23 pm Dear Mr. Jignesh, Kindly use reference and standards. This ‘ll help us to improve the knowledge about standards and it ‘ll also induce to search about the standards. -Paramasivan Tsp (My FB id) Reply Jignesh.Parmar says:

January 29, 2014 at 1:51 pm Normally I always indeed to indicate Standard and mention for the same..But where it is not possible,it is not mentioned.. as in the case of “THUMB RULE” Reply karan says:

February 21, 2014 at 12:15 pm what about alluminium cable? Reply prakash parmar says:

March 1, 2014 at 10:29 am Dear sir, I m gating regular mail Its a very use full information from for me Thank you Reply [email protected] says:

July 8, 2014 at 5:58 am Dear Which rule have you followed for cable current carrying capacity? Reply ikoh says:

July 10, 2014 at 10:35 am thank you for all the information!!! Reply kashyap raval says:

August 4, 2014 at 2:45 pm Dear Sir, Thanks a lot for such technical information which will help to solve day to day workings. It is reallya most valuable and sound as well as perfect calculations .. Please be in touch by mail, I shall be grateful if send me such an electrical related informations,calculations etvc. Reply rajvasanth1983 says:

September 24, 2014 at 5:56 am Dear sir, Thanks for your lot of Technical information.



One our customer in UK.Their asking for Below ground earthing calculation used BS (british standard).But I have IEEE80 format Ex sheet. Their not accepting IEEE80. Hence.Hence Kindly send the BS format for below ground earthing. This is very useful for Us. Regards V.vasantha kumar. Reply Jose says:

October 7, 2014 at 12:46 pm Dear Sir, can you prepare thumb rule based on DEWA regulations. Reply Mohanty says:

November 8, 2014 at 2:42 am Gud information for public knowladge.. Thanks lot. Reply Lakshman prasad Gupta says:

January 21, 2015 at 6:44 pm In domestic wiring, if neutral line is shotred with housing earth line, What problem we can face? Whether it will effect on K WH meter reading? Is there any chances of ge ing my electronic equipments damage? Reply GK says:

January 28, 2015 at 8:33 am Excellent information. LIVE LONG DEAR ENGR JIGNESH. GK Reply parag says:

June 11, 2015 at 2:25 am WHAT IS 10X RULE IN VOLTAGE DIVIDER CIRCUIT Reply Aditya sharma says:

August 1, 2015 at 6:10 am Sir its wonderful knowledge is here i m very thankful to u . Jagnesh ji Reply

Blog at WordPress.com. The Enterprise Theme .

Electrical Thumb Rules-(Part 1)

Recommend Documents