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Sunday, December 13, 2015

Formula Selection of ELCB & Brach MCB of DB

 Formula Selection of  ELCB & Brach MCB of DB

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

Calculation:

Size of MCB for Branch Circuit-1:

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

Size of MCB for Branch Circuit-2:

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

Size of MCB for Branch Circuit-3:

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

Size of MCB for Branch Circuit-4:

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

Size of MCB for Branch Circuit-5:

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

Size of MCB for Branch Circuit-6:

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

Size of MCB for Branch Circuit-7:

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

Size of MCB for Branch Circuit-8:

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



  1. Total Load Current as per NEC= 18.04Amp——–(A)
  2. Max Size of Branch circuit MCB=16Amp
  3. Total Current of Panel as per Branch Circuit= 2X Max Size of Branch circuit MCB
  4. Total Load Current of Panel as per Branch Circuit =2X16=32Amp——(B)
  5. Total Load Current of Panel as per NEC = Maximum of (A) and (B)
  6. Total Load Current of Panel as per NEC=32Amp
  7. Min Size of ELCB/RCCB as per NEC=40Amp
  8. Class of ELCB/RCCB= B or C Class
  9. No of Pole of ELCB/RCCB=TP or FP
  10. Sensitivity( I∆n)=30ma
  11. Breaking Capacity=10KA

Size of Distribution Board:

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

Load Balancing of Distribution Board:

  1. To Balance Load We need to try distribute Single Phase load on each Phase.
  2. 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 :

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

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