Electrical. Q&A

Collection of  Electrical Questions and Answers:

Electrical Question and Answers Part-1

Electrical Question and Answers Part-2

Electrical Question and Answers Part-3

117 Responses to Electrical. Q&A

  1. Pranav Jani says:

    Hi Jignesh,

    first of all, many many thanks to organise such a informative contents of electrical engineering. I appreciate this a lot. I have gone through many websites but didnt found so much useful information which I found on your website..brave effort.

    My electrical background is not so fundamental so would like to ask u a question regarding underground cabling of medium voltage cables for pv projects.

    I m looking for indian standards of medium voltage and low voltage cable specification for mega watt pv project.

    Will u pls guide me on this?

    Thank you.

    kind regards,

  2. G.R.Prasad says:

    What is the minimum clearence required around the neutral CT used for REF protection in 415V system.

  3. Senthilkumar says:

    please give details about SC rating design details for MDB and SMDB bus bars

  4. nalini says:

    nice question and answers sir,its very good…

  5. vishwa murthy says:

    Dear Jignesh ji,

    I want to know how to calculate the string efficiency, can you please send/post the details…it will be most helpful for me.

  6. Gnana Reuben says:

    Dear Jigneshji

    Thnaks a lot for the Current ratings, Gland Chart and Q&A Part 1 thru 3

  7. Madhurjya says:

    State whether a lamp rated for 230 V, 60 W can be used for both a.c & d.c supply. Give the reasons to your answers.

  8. selvanayagam.a says:

    hai sir.your Q/A everything useful.but how down load for pdf that about explain me

  9. Adil says:

    Thank u and please keep going

    Very good job

  10. Tshwarelo says:

    I enjoyed data that i got here.

  11. Jones says:

    Its really awesome,

  12. kuppuraj says:

    thank you sir…………………..!

  13. NEHA GETHE says:

    its 2 gud sir…..

  14. kandasamy says:

    very very useful site

  15. dear jignesh sir,
    i want to know that is there any chances of load on energy meter if indivisual neutral is not provide?

  16. how to calculate the current of a transformer?

  17. elias says:

    i like ur page thanks a lot cause i imrove my knowledge. thanks a lot.

  18. Pravin mali says:

    Nice site.thanks sir.

  19. Eneyo Duke says:

    Please is DOL applicable to lamp or only motor?

  20. Watch Dogs Ps3 says:

    I’m impressed, I must say. Seldom do I come across a blog that’s equally educative and amusing, and let me tell you, you have
    hit the nail on the head. The issue is something too few people are speaking intelligently about.

    I am very happy I found this in my search for something concerning this.

  21. m.balagurunathan says:

    Differences between providing the MCC with and without the relays.

  22. john says:

    2. A final circuit consists of six heaters connected in parallel each having a resistance of 150Ω. Find (i) the total resistance of the circuit (ii) the current through each resistor if the supply voltage is 600 V.

  23. parikshit gorai says:

    thanks for your valuable notes regarding cable trays.

  24. Francis lungu says:

    what is maximum mega ohms on 11kv 3core cable

  25. sureshbabu says:

    good evening sir, what is genarators check list and genaral maitanance

  26. Appeagyei says:

    Hi Engineer Jignesh,

    I know loss of neutral on a 3 phase system causes voltage on phase with less load to rise and that of the phase with high load to fall. please explain how and why this happens

    Thank you

    • The absence of Neutral will cause the total voltage to rise upto 380V between 2 phases. So as per voltage dividing rule it acts as a serious combination of two parallel branches if without earth or neutral in between. Hence the serial branch which has more LOADS ( means effective resistance low because parallel connection ) will hae less voltage across it. Remember current is same.

  27. Danish says:

    hi jignesh
    can you help me out regarding , what we have to see or note the important points when we are reading the specification for the electrical equipment eg ..transformer, ups , fire alarm ,cctv, acess control , hv switchgear , busbar ,mdb ,smdb, etc can you please help me out on this
    and keep going

  28. RamKumar says:

    sir, How to do Hi-pot test (DC)

  29. Vinoth Kumar says:

    Thank You very much for this collection sir.. It helped me in my career.

  30. weljoe says:

    What is the acceptance resistance of low voltage cables?

  31. vidya says:

    Its a very good explanation..very clean nd clear. .soo great..thaank uu sir.

  32. Akif Qadeer says:

    How to choose Accuracy class of CT?
    Lets say Meter is of 0.5S or 0.5 accuracy!!

  33. bramhanand says:

    sir i want to know about the dynamic impedance of ht motor at the time of start

  34. Saiju Joseph says:

    Dear Jignesh.Parmar,

    How i calculate capacitor bank breaker (ampere) capacity ?..example 80kvar capacitor if i connect in MDB,

  35. Vishnu G says:

    I wants to know about different ferrules and its meaninga

  36. P M Pavan Kumar says:

    Dear Sir,
    When we connect the capacitor bank to the motor, will it draw current continuously or not? Please reply.

  37. Hlonie says:

    What causes inductance in a circuit

  38. c.b singh says:

    hello sir
    i have a question that if i have a sub station with a transformer capacity 5MVA i have to erect 3 feeder of 18 to 20 Km each then how can i select size of conductor. these feeder are for rural areas

  39. Amrit Kumar Mohanta says:

    Hello Sir,
    My question is regarding on power flow analysis. I want to know that, what is the X/R ratio of Grid. It is require for simulating in ETAP

  40. Pankaj tiwari.k says:

    Why motor ratings are in h.p not in kw?

  41. tony says:

    hae,i acknowledge the good work on this website..l am an electrical engineering graduate at diploma level however the job market is flooded.i would like to pursue plc programming studies to add value to my carreer path…at what degree will it enhance my chances in the job market?

  42. MOHAMED HAROON says:

    who is best electrical conduit for lighting and socket

    A) Rigid Non Metallic Conduit (PVC)
    B)Rigid Metal Conduit (RMC) / Rigid Steel Conduit (RSC)
    C)Intermediate Metal Conduit (IMC)
    D) Galvanized Rigid Conduit (GRC)
    E)Electrical Metal Tubing (EMT)
    F) Flexible Metal Conduit (FMC)

  43. Bassey Friday says:

    How to calculate correct cable size for a 37kw ac motor and the correct gen for. A factory with 950kw load

  44. Tarun says:

    I have a project to design a food court in kundali. in this there are two nos. of coffee shop, one nos. KFC outlet & 12 nos of small FNB outlets of 600 sq.ft. area.
    I have to prepare a electrical load sheet.i’m confused how much load should i take, my senior suggest take 100kW for KFC and 40kW for coffee shop & 20kW for rest of the outlets.
    But it seems too much load we have taken.
    & how much diversity we would take?
    Please help sir what to do.

  45. Danish Hayat says:

    Dear Sir
    Could you plz help me out regarding the diversity factors to be considered for different panels . Do i have to consider diversity factor for all MDBs & finally diversity factor in main LT panel . Is there any code which says about diversity factors at different levels of distribution.

  46. Pradeep Khandagale says:

    Good morning ,
    Jiganesh sir,
    I want Indain standaras; & NEC Rules For E.H.V. Transmission line & EHV substation up to 400 kv.
    Thank you.

  47. saumya says:

    how can i calculate current carrying capacity of copper wire

  48. Hi sir, I am so happy to know your side…I want to know how a tube-light work.and it circuit diagram…estimation and cost.

  49. suresh says:

    Hi Sir,
    I have charged 132 KV S/C Line 35.9 Kms in length . There was no terminal equipment like LAs & CVT at receiving end . This line remained charged for more than a month and then whole assembly of R_phase got punctured further lead to snapping of conductor at T8 near to receiving end. Kindly let me know whether the above breakdown was due to Ferranti effect of the line or weak insulation of Disc insulators or high earthing resistance of line ?

  50. Ravi kant says:

    nice Q.

  51. tanzeel says:

    Hello everyone. Can any body tells me that RCBO C32 and R30 100mA, in this RCBO, what is meant by C in C32 and R in R30??

  52. prabhat says:

    very good info

  53. Shreyas says:

    caterpillar 1000kva .800 kW ..stops automatically in between what may be reason ?

  54. All electrical q&a sending for my mail ID

  55. Sameer Bhoi says:

    i never seen this type of website to learn about electrical.

  56. Sandeep says:

    Our vertical flange mount motor with centrifugal pump driven motor capacity 70 KW 3 ph Induction motor become vibration when motor run through VFD.

    Vibration occur only 1200 RPM to 1350 RPM DE-NDE V- 5.9 mm/s H- 7.9 mm/s A- 1.2mm/s. If motor run at full load then vibration is normal below 2.5 mm/s.

    What is actually problem. i am also take vibration at no-load also but same problem.

    I am also changed motor at foundation but same problem observed.

    Please give me technically ans….

    Sandeep Dalal

  57. Hothifah says:

    I am an electrical engineer and I am still fresh. I am studying the Steam turbine Generator and I have an STG connected to a grid (60 Hz,34.5 KV), the output STG power is 26 MW I need to increase it to 31.2 MW. I need to focus into generator side not prime mover. The question,

    1- What is the primary step I should do ?
    2- What graph should I study (Capability curve, v/f .. etc) ?
    3- How can I know what is the maximum Active power ?
    4- What is the logic and control that prevent the generator to feed more ?

    I appreciate your help..


  58. question says:

    question:estimate the material required for cts wiring system used in a hall measuring 30’*60’and height 10’and the reuirements are as follows: no.of lights points=32.no.of fan points=6.no.of 2pin plug sockets=2

  59. HARSHAD KOLI says:

    GREAT support

  60. Nikhil says:

    Thank q for providing such a website for electrical information

  61. Hardik Kotadiya says:

    Good question nd answer

  62. Dear sir,

    what will happen if we are not done earthing or disconnect earthing the switch gear (33kv switchboard indoor type)all CT & PT Star points are connected to same earth bus

  63. eihtwe says:

    Thanks a lot for your sharing.Your notes are very effective to me.

  64. Vijay Yadav says:

    . Due to this improve my basics

  65. Thanks Boss. Tapas Banerjee

  66. sri alex says:

    what is meant by safety factor in electrical??
    how can calculate the safety factor??
    plzz answer me fast..


  67. Faheem says:

    I have a chiller which is consuming 1.2 MW of power daily and voltage is 4.160V.How to calculate it in kWh?

  68. Emil John Candelario says:

    Hi Jignesh. We are procuring a submersible pump together with a separate terminal box and the area classification for the equipment is Zone 1 Group IIA T1. Our vendor is suggesting that a T6 rated equipment is superior to a T1 rated equipment. I have seen the T-class table for explosive atmospheres and there is a big difference between the two. Is our vendor correct in saying that a T6 rated equipment is superior to a T1 rated equipment? If possible, can you also please send to me the regulation, preferably IEC, which shows how to interpret the T-class for such an equipment. Thank you so much and your help is very much appreciated.

  69. Hariprasad says:

    what will happen If u give a same body earthing for AC and DC equipment’s?

    • Girish R Pillai says:

      Nothing will happen if you make sure that the earth is a perfect one with the lowest of the lowest ohms. Make 3 pits minimum and interconnect in delta and bring minimum 2 earth conductors from diagonal points of each equipment.

  70. Thangavelu Kumnar says:

    In which base REF protection act as earth fault protection explain please

    • Girish R Pillai says:

      R.E.F acts for faults in between the incoming side and outgoing side CTs of a transformer. This region can’t be protected by the C.Ts alone, as they may not get any fault currents in such a situation. Hence the protection circuit is made up with another logic involves the unbalanced currents.

  71. Thamizh says:

    Hello..sir. what is the procedure to remove moisture from HT panel.

  72. Dear Mr.Parmar,

    Many many thanks for preparinfsuch beutiful and useful information for Electrical engineers .Many webistes just give supoerficila information and then ask your persional details for obvious reasons (selling it).

    My sincere tahnks to you and keep it on.

    Chandrakant Ghan

  73. Dear sir
    In detailed lecture you have provided many useful information please advice whether any specific calculations or specified rules to be followed for calculating the length of gap in for multi gap (series gap) lightning arresters

  74. nikunj says:

    sir please send me your e mail id..

  75. Manish kumar Chaudhary says:

    what’s kelvin’s law

  76. Ameen Basha says:

    In my project, there is a 132kV Shunt Reactor. what voltage grade cable will be used for solid earhting the neutral.kindly advice.

  77. pradeep says:

    Electrical related

  78. shirish says:

    dear sir
    i want to know the maximum distance in meters illuminated by high mast lights on road.
    want to illuminate around 8 km zigzag road. even maximum area illuminated by one high mast light will also do.

  79. Honorato Acebedo says:

    Dear Sir Parmat, i have 3.3kv genset can i add a low voltage generator using step up transformer? can i synchronize it to 3.3kv.
    waiting for your reply thanks….

  80. Ravi.s says:

    what is the purpose of using Resistor+Capacitor unit (RC circuit)?.
    Need surge suppressor(RC unit) to prevent ‘very fast Transient voltage’ during operation of Switchgear.

  81. Prashant rajak says:

    We are having 220 V DC battery bank system for supplying control supply to our 220 KV Switch yard. we are facing the problem +ve to ground fault in our Battery bank Dc system. can any one having idea how to find the DC leakage without switching OFF the connected load.

  82. The Information you added its very useful….Thank you so much….

  83. Ahmed Eissa says:

    If I have MAN diesel generator 800 kva standby and I need to test sudden load with load what is the maximum load according the ISO?

  84. venkatesh.b says:

    Give objective type questions about machines

  85. sunil says:

    Hi sir
    First of all, many many thanks to organize such a informative contents of electrical engineering. I appreciate this a lot.
    i want to contact with you so need a your contact number

    Thanking sir
    +919481189609 My whats app no
    +917030931925 contact no

  86. safwan k says:

    hello sir, can u give the details of leackage current limit, when doing the 13.8 kv cable hv

  87. safwan k says:

    dear sir…
    can you give the details of leakage current limit for 13.8 kv cable hv testing.


    Very nice.
    I would like to ask a question.
    A 132/33 kv substation is feeding power from two different sources and the sources are 1) 220/132 kv substation at a distance of 5 kms 2) A generating station at a distance of 36 kms.
    Now the 132/33 kv substation has a 33 kv feeder of fluctuating load( 20 amps to 300 amps).
    The ampere meter of the feeder coming from 220/132 kv substation is more fluctuating than the generating one.
    Please tell me.

  89. bengabi says:

    hi if i step up dc to ac like from 4v dc to 500v ac would the amps also increase as much as the volts. question 2 in an inverter circuit diagram i saw three ground symbol one from the negative terminal of the battery do i have to physically dig a hole and put an earth there or is there any other way out to make it cheaper

  90. Gwamna Abel says:

    what is the require height of the thunder arrestor of building that is 15 meters?

  91. Sarang Mehetar says:

    It is very useful site.Thank you.

  92. GANESH says:


  93. saravanan says:

    the difference between earth resistance and earth electrode resistance?

  94. Rakesh says:

    What is the distance between two bus bar, phase to phase

  95. Sthitodhi mukherjee says:

    I am sthitodhi mukherjee ,wbsetcl,junior engineer (electrical) postted at burdwaman 132kv substation.l have read of ur all docoments and learn many things and thank u for share ur vital docoments.
    I have requested to u how to design substation grounding and relay panel design ?

    Thanking u

    Sthitodhi mukherjee

  96. abhinav srivastava says:

    what is the differnce between switch and starter?

  97. cleanwell says:

    so so useful, how i wish all electrical engineering personnel’s should subscribe here.

  98. cleanwell mudenda says:

    so so useful, how I wish all electrical engineering personnel’s should subscribe

  99. Rohit Daddikar says:

    Dear Sir,

    I am working as Safety Executive in construction industry. I am working with Adani Contractor in Shantigram Project. Ahmedabad. I have confusion about Lightning arrestor. I want to know as per IS what is the minimum height required for fixing lightning arrestor? Is there any formula or any location/area required for fixing? Please guide me.

    Thanking You
    Rohit Daddikar

  100. Anto Shiyam Prakash says:

    Dear sir,

    we have LPG storage bullet with capacity 25 MT in our company. And there is a work in progress for installing 110KVA HT line over it. We afraid of safety in that case. What will be the minimum clearance between the LPG bullet and HT line to ensure safety. Kindly help me out on this issue.

    Thank you,
    Anto Shiyam Prakash. D

  101. GIRISH says:

    Not possible at all

  102. deepla says:

    Dear sir,
    how to select transformer termination HV side,cable box termination or direct to connect on bushing?.and please given with rating

  103. sadashiv salaskar says:

    nice content sir i really loved and i think i never see such a content at one page awesome

  104. kiran sahu says:

    Very Useful for all the Freshers.
    Thank You for sharing these important questions with us. Answer sounds more confident. This article motivated me.. thank you..!!

  105. shantilal says:

    Dear Jignesh Sir
    Is it possible to synchronize CAT 2000 KW & Cummins 2000 KW DG sets on same synchronizing panel. Is yes than how, If not, than why? Can you please clear my doubt.
    shantilal parmar

  106. NASEEM says:

    Dear Sir

    Can you guide me?
    How much Load we consider for 6/16 A switch sockets as per standard ?

  107. Akande ganiu says:

    How to derive neutral in a transformer

  108. Lima imsong says:

    I bought electric pole and wire to divert power supply line from my land as the power department asked me to do so. Today the power department has abondoned the pole. Do I have rights to claim the pole and wire I bought?

  109. vikas says:

    Sir Please give the mechanical design related imortant notes

  110. sagar parmar says:

    sir can you please explain how demand/fixed charges, wheeling charges, energy charges calculated in electricity bill of commercial load.

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