Calculate Size of Main ELCB & Brach MCB of Distribution Box

Design Distribution Box of one House and Calculation of Size of Main ELCB and branch Circuit MCB as following Load Detail. Power Supply is 430V (P-P), 230 (P-N), 50Hz. Consider Demand Factor 0.6 for Non Continuous Load & 1 for Continuous Load for Each Equipment.

• Branch Circuit-1: 4 No of 1Phase, 40W, Lamp of Non Continues Load + 2 No’s of 1Ph, 60W, Fan of Non Continues Load.
• Branch Circuit-2: 2 No of 1Ph, 200W, Computer of Non Continues Load.
• Branch Circuit-3: 1 No of 1Ph, 200W, Freeze of Continues Load.
• Branch Circuit-4: 8 No of 1Ph, 40W, Lamp of Non Continues Load + 2 No’s of 1Ph  60W, Fan of Non Continues Load.
• Branch Circuit-5: 4 No of 1Ph , 40W, Lamp of Non Continues Load + 1 No’s of 1Ph 60W, Fan of Non Continues Load.+ 1 No’s of 1Ph 150W, TV of Continues Load
• Branch Circuit-6: 1 No of 1P , 1.7KW, Geyser of Non Continues Load.
• Branch Circuit-7: 1 No of 1Ph, 3KW, A.C of Non Continues Load.
• Branch Circuit-8: 1 No of 3Ph, 1HP, Motor-Pump of Non Continues Load.

 Fault Current Voltage Fault Current 230V 6KA 430V 10KA 11KV 25KA
 Class of MCB/ELCB/RCCB Type of Load Class Sensitivity Lighting B Class I∆n:30ma Heater B Class I∆n:30ma Drive C Class I∆n:100ma A.C C Class I∆n:30ma Motor C Class I∆n:100ma Ballast C Class I∆n:30ma Induction Load C Class I∆n:100ma Transformer D Class I∆n:100ma
 Size of MCB/ELCB Current (Amp) Lighting Load MCB/ELCB (Amp) Heating/Cooling/Motor-Pump Load MCB/ELCB (Amp) 1.0 to 4.0 6 16 6.0 10 16 10.0 16 16 16.0 20 20 20.0 25 25 25.0 32 32 32.0 40 40 40.0 45 45 45.0 50 50 50.0 63 63 63.0 80 80 80.0 100 100 100.0 125 125 125.0 225 225 225.0 600 600 600.0 800 800 800.0 1600 1600 1600.0 2000 2000 2000.0 3000 3000 3000.0 3200 3200 3200.0 4000 4000 4000.0 5000 5000 5000.0 6000 6000 6000.0 6000 6000

Size of MCB for Branch Circuit-1:

• Load Current of Lamp= (No X Watt X Demand Factor)/Volt =(4X40X0.6)/230=0.40Amp
• Load Current of Fan= (No X Watt X Demand Factor)/Volt =(2X60X0.6)/230=0.31Amp
• Branch Circuit-1 Current as per NEC = Non Continues Load+125% Continues Load
• Branch Circuit-1 Current as per NEC =(0.4+0.31)+125%(0) =0.73Amp
• Class of MCB=B Class
• Size of MCB=6 Amp
• No of Pole of MCB=Single Pole

Size of MCB for Branch Circuit-2:

• Load Current of Computer = (No X Watt X Demand Factor)/Volt =(2X200X0.6)/230=1.04Amp
• Branch Circuit-2 Current as per NEC = Non Continues Load+125% Continues Load
• Branch Circuit-2 Current as per NEC =(1.04)+125%(0) =1.04Amp
• Class of MCB=B Class
• Size of MCB=6 Amp
• Breaking Capacity: 6KA
• No of Pole of MCB=Single Pole

Size of MCB for Branch Circuit-3:

• Load Current of Freeze= (No X Watt X Demand Factor)/Volt =(1X200X0.6)/230=0.87Amp
• Branch Circuit-3 Current as per NEC = Non Continues Load+125% Continues Load
• Branch Circuit-3 Current as per NEC =(0.87)+125%(0) =0.87Amp
• Class of MCB=B Class
• Size of MCB=6 Amp
• Breaking Capacity: 6KA
• No of Pole of MCB=Single Pole

Size of MCB for Branch Circuit-4:

• Load Current of Lamp= (No X Watt X Demand Factor)/Volt =(8X40X0.6)/230=0.83Amp
• Load Current of Fan= (No X Watt X Demand Factor)/Volt =(2X60X0.6)/230=0.31Amp
• Branch Circuit-4 Current as per NEC = Non Continues Load+125% Continues Load
• Branch Circuit-4 Current as per NEC =(0.83+0.31)+125%(0) =1.15Amp
• Class of MCB=B Class
• Size of MCB=6 Amp
• Breaking Capacity: 6KA
• No of Pole of MCB=Single Pole

Size of MCB for Branch Circuit-5:

• Load Current of Lamp= (No X Watt X Demand Factor)/Volt =(4X40X0.6)/230=0.42Amp
• Load Current of Fan= (No X Watt X Demand Factor)/Volt =(1X60X0.6)/230=0.16Amp
• Load Current of TV = (No X Watt X Demand Factor)/Volt =(1X150X1)/230=0.65Amp
• Branch Circuit-5 Current as per NEC = Non Continues Load+125% Continues Load
• Branch Circuit-5 Current as per NEC =(0.42+0.16)+125%(0.65) =0.57+0.82=1.39Amp
• Class of MCB=B Class
• Size of MCB=6 Amp
• Breaking Capacity: 6KA
• No of Pole of MCB=Single Pole

Size of MCB for Branch Circuit-6:

• Load Current of Geyser= (No X Watt X Demand Factor)/Volt =(1X1700X0.6)/230=4.43Amp
• Branch Circuit-6 Current as per NEC = Non Continues Load+125% Continues Load
• Branch Circuit-6 Current as per NEC =(4.43)+125%(0) =4.43Amp
• Type of Load=Heating & Cooling Type
• Class of MCB=C Class
• Size of MCB=16 Amp
• Breaking Capacity: 6KA
• No of Pole of MCB=Single Pole

Size of MCB for Branch Circuit-7:

• Load Current of A.C= (No X Watt X Demand Factor)/Volt =(1X3000X0.6)/230=7.83Amp
• Branch Circuit-7 Current as per NEC = Non Continues Load+125% Continues Load
• Branch Circuit-7 Current as per NEC =(7.83)+125%(0) =7.83Amp
• Type of Load=Heating & Cooling Type
• Class of MCB=C Class
• Size of MCB=16 Amp
• Breaking Capacity: 6KA
• No of Pole of MCB=Single Pole

Size of MCB for Branch Circuit-8:

• Load Current of Motor-Pump = (No X Watt X Demand Factor)/(1.732XVolt ) =(1X746X0.6)/(1.732X430)=0.60Amp
• Branch Circuit-8 Current as per NEC =Non Continues Load+125% Continues Load
• Branch Circuit-8 Current as per NEC =(0.60)+125%(0) =0.60Amp
• Class of MCB=C Class
• Size of MCB=16 Amp
• Breaking Capacity: 10KA
• No of Pole of MCB= Three Pole

Size of Main ELCB/RCCB:

• Total Brach Circuit Load & MCB Detail is
 Brach Circuit Total Current (Amp) Size of MCB (Amp) Class of MCB Breaking Capacity of MCB Pole of MCB circuit-1 0.73 6 Amp B Class 6KA SP circuit-2 1.04 6 Amp B Class 6KA SP circuit-3 0.87 6 Amp B Class 6KA SP circuit-4 1.15 6 Amp B Class 6KA SP circuit-5 1.39 6 Amp B Class 6KA SP circuit-6 4.43 16 Amp C Class 6KA SP circuit-7 7.83 16 Amp C Class 6KA SP circuit-8 0.63 16 Amp C Class 10KA TP Total 18.04
• Total Load Current as per NEC= 18.04Amp——–(A)
• Max Size of Branch circuit MCB=16Amp
• Total Current of Panel as per Branch Circuit= 2X Max Size of Branch circuit MCB
• Total Load Current of Panel as per Branch Circuit =2X16=32Amp——(B)
• Total Load Current of Panel as per NEC = Maximum of (A) and (B)
• Total Load Current of Panel as per NEC=32Amp
• Min Size of ELCB/RCCB as per NEC=40Amp
• Class of ELCB/RCCB= B or C Class
• No of Pole of ELCB/RCCB=TP or FP
• Sensitivity( I∆n)=30ma
• Breaking Capacity=10KA

Size of Distribution Board:

• No of Single Pole Branch Circuit MCB (SP)= 7 No’s
• No of Three Pole Branch Circuit MCB (TP)= 1 No’s
• Main ELCB (TP)=1 No’s
• Total No of Way of D.B (SPN)= (SP)+3X(TP)=7+(3X2)=13Way SPN
• Total No of Way of D.B (TPN)= (SP)/3+ (TP)=(7/3)+(2)=4+2=6Way SPN
• Select Either 14Way SPN or 6 Way TPN

• To Balance Load We need to try distribute Single Phase load on each Phase.
• Suppose We connect Branch Circuit load on following Phase
 Brach Circuit Current (Amp) Type of Load Connection on Branch circuit-1 0.73 Single Phase Y Phase Branch circuit-2 1.04 Single Phase B Phase Branch circuit-3 0.87 Single Phase Y Phase Branch circuit-4 1.15 Single Phase B Phase Branch circuit-5 1.39 Single Phase Y Phase Branch circuit-6 4.43 Single Phase B Phase Branch circuit-7 7.83 Single Phase R Phase Branch circuit-8 0.63 Three Phase RYB Phase Summary of Load R Phase Load 8.5 Amp Y Phase Load 3.5 Amp B Phase Load 7.23 Amp Total Load 18.04 Amp

Summary of Distribution Box :

• Size of Distribution Box : 14Way SPN or 6 Way TPN
• Size of Main ELCB: 40A,B or C Class,30ma,10KA
• Size & No of Branch MCB: 5 No’s of 6A,SP, B Class,6KA
• Size & No of Branch MCB: 2 No’s of 16A,SP, C Class,6KA
• Size & No of Branch MCB: 1 No’s of 16A,TP, C Class,10KA

Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 14 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 "Electrical Mirror" and "Electrical India" 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.

55 Responses to Calculate Size of Main ELCB & Brach MCB of Distribution Box

1. Vilas Garde says:

Dear Sir, Very Nice information on Electrical. Do you have such link for Instrumentation also if so please send link..? RegardsVilas Garde

2. Raju says:

Thank you Sir,

3. V.P Selvam says:

Dear Jignesh sir,,,
I m selvam working in ISRO as an Electrical Engineer, It is very useful material for everyone who wants to select the ELMCB nd MCB, DB…i really enjoy reading ur all blogs nd it gives me a clear idea and all practical concepts..i wish to continue ur valuable nd wonderful efforts…thanking u sir…

4. vijay s says:

That is a good example. How to design an Electrical panel board and do the wiring ? Also, what are the useful software available in the market to do that?
Thanks and regards,

5. naga mahesh says:

SUPER SIR IT IS REALLY VERY HELP FULL TO ME SIR . BECAUSE I AM A FRESHER AND I STARTED MY WORKING WITH OUT PRACTICAL KNOWLEDGE……AND ONE MORE HON ABLE REQUEST IS PLEASE MAIL BUILDING CONSTRUCTION RELATED ELECTRICAL TOPICS MEAS CALCULATION……………………PLEASE SIR

6. Eng.Elifuraha Mmary says:

Am very interested on article of sizing CB,
My request is, if possible let me have full topic of switchgear where I can help other on proper electrical installation and utilisation as well.
Thanks
Even a short course as right now am working in academic institution from Tanzania.

7. bharat bhushan says:

hello sir,
I am using a 2 pole,30ma sensitive rccb on the main line for the entire house.All the phase and neutral connections are done from the output of the rccb.I have one inverter/ups also which is getting the power supply from the output of the rccb.I want to connect a separate rccb on the output side of the inverter connection,but for this i am not able to find the proper way to connect the new rccb. if i am connecting the o/p from inverter and the same neutral,which is used for the power supply of the inverter as the i/p of new rccb and the single load wire(phase) at the output with leaving the neutral pole as it is then the new rccb trips.If i short both the i/p and o/p neutral of the new rccb and connecting the phase as above then also the new rccb trips .i guess there is some problem regarding neutral looping.please suggest me the proper way of connecting the rccb.

8. Mahesh says:

good info. Is it possible to conduct basic design induction in Mumbai? In case interested then it can be discussed

can you please tell me why you are not multiplying the calculated load current with 125% for branch Ckt calculation. as its non continuous load mentioned by you in the beginning.

10. Eswaran says:

This is very useful for those who are in construction field.

11. Eswaran says:

Where to fix the Z CT in HT Cable. i.e only three core or three core with earth. please explain with diagram sir.

12. Naga Mahesh says:

sir send and update s of electrical calculations please

13. Noor khan says:

Sir for Current Calculation we use formula I =P/V x (Power factor )
Or I =P/V x (Power Factor) x(1.73)
But here You used I =P x (Power Factor)/V
Plz Sir explain

14. Muthazhagan says:

dear sir,
what size of wire should be used for Light Points,fan points,etc and how many runs [ 2 or 3 runs]

15. Deepak says:

hello Sir,

Can we use a 400v main mcb double pole in a 240v supply.will it trip or work same as a 240v breaker?

Thnx fr

Deepak

16. MS Karoly says:

Is there an article who to do this calculation as per IEC?

17. MS Karoly says:

Do you have calculation as per IEC standards?

18. Navnath M T says:

Your notes r very useful for to study for any kind of installation of an electrical equipment. Thanking you

19. B.D. says:

ur notes are awesum

20. Mufutau Ibrahim Engn. Techn says:

Tanx for a very wonderful job. May Almighty Allah guide you right

good

22. sandaruwan says:

sir, very nicely understand every things thanks for u

23. Phyoko says:

Thank you very much for your kindly Sir;

24. Phyoko says:

Thanks

25. Hussain says:

Dear Sir,

Thanks for the useful informations. But the formula for calculating the load you used in all circuits the demand factor must be down not up! Am I correct? I= (no. * P)/(1.7*V*Factor)

26. Dhruvesh patel says:

Hi……..SIR…..
I WORK IN ONGC AS ELECTRICIAN.ON A FIRST DATY OF
MY JOB I FOUND THAT THERE IS TWO PHASE SHOWS IN 5A AND 15 A PLUG
SOCKET OF 110 VOLTS EACH . HOW CAN AMPLIENCES WORK ON TWO PHASE OF
110 VOLTS WITHOUT NEUTRAL.?? AND WHEN I ASK FOR THAT TO MY SENIOR HE
TOLD ME THAT THIS IS RULE IN ONGC THAT THEY CAN NOT USE NEUTRAL FOR
LIGHTING PURPOSE. BUT HE HAD NO REASONE FOR THAT. CAN YOU HELP ME TO
UNDERSTAND THIS

27. rao mohan says:

why multiplie 125 %

28. Prashant says:

Dear Jignesh sir,,,
I m selvam working in ISRO as an Electrical Engineer, It is very useful material for everyone who wants to select the ELMCB nd MCB, DB…i really enjoy reading ur all blogs nd it gives me a clear idea and all practical concepts..i wish to continue ur valuable nd wonderful efforts…thanking u sir…

29. Farooq Ahmed says:

Dear sir please let me know for 20hp power what
size of elcb rccb is required
Asap

30. fazal rehman says:

fault currents are given for 1second or more time plz add answer?

31. arif says:

sir can u please suggest if i have 30 volt bulb then how to count watt and ampere for it

32. dr.pvs raju says:

dear parmer,it is wondrful information given by u.i think crores of indian population need to read and learn about this house electricity information.i am 71yrs and i learn from u which i have been waiting to learn this basics.thanks

Dear Sir, Thanks alot for providing a clear article on this topic. I enjoyed reading.

34. sandeep says:

Sir,
I think all the phases (R,Y,B) have to be equal load and balanced. but here r=8.5,Y=3.5,B=7.23 Watts. For a balanced connection phases should have equal loads.

35. SHIVANNA says:

Nice sir,
Sir i need how to calculate the cable sizing for the building from transformer centre .

36. harsha says:

can you tell me formula to calculate breaking capacity of MCB for load 200W 415V with 5% impedance n transformer ratings are 1500KV

37. er mohd irfan wani says:

Current rating of mcb

38. How much ELCB required for 48 AMP load extension

39. Ritesh M Patel says:

I’m working for many years but no one explain me like this, thank u so much sir.

40. Victor Alwyn says:

Sir should you go for mcb board for Microwave oven

Good day Sir,

I am trying to size a MCB for a 3 phase 380Vac, 2.5kW motor. and based on what I ended up calculating was a MCB of the size 16A with a fault current of 10kA, will this work?

42. saurav says:

sorry ac is single phase load.

43. Smruti Samal Bhuyan says:

Dear Sir,
Could you explain the load balancing. Here load is not balanced, in a ckt the load current is 3.5 A which is more less than other two ckts.???

44. selvakumar says:

Hi how to determine demand factor ?

45. ashok kumar says:

thank s

46. Mahendran Ravichandran says:

Thanks alot sir

47. Aasif khan says:

Sir in your above calculation of selection of MCB i want to ask a question i.e. in your branch circuit no. 3 you have include the freeze in a non continuous load why? and what is the us

48. Sukanta Chanda says:

Its very useful article or information to choose proper mcb,rccb etc. I am a local electrician . Its increase my confidence more than before. Its very very helpful fo me. Thank you.

49. yogesh nagare says:

thanks sir

50. TONY JOSEPH says:

63A MCCB 25 KA- WHAT IS 25 KA ? How will i find out the ka rating of MCCB?

51. siti faezan noor farah mohd noor says:

Branch Circuit-3: 1 No of 1Ph, 200W, Freeze of Continues Load.

but why did u calculate its load current as a non continuous load sir? can u explain?

52. laxman Dhawale says:

sir
this is very helpful and nice
and can you give details of cable size and selection all like internal wiring and LT/HT cable.