Ampere Electrical Contracting Est

Ampere Electrical Contracting Est
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Thursday, February 17, 2011

Cable Size Calculation

  2. Calculate the Demand Load or Connected Load Ic = P/1.732 * V * p.f.
  3. Choose the Next Size of Circuit Breaker In = ( CB =Ic).
  4. Cable Size = (CB x 1.15) /(Ft *Fg)
{ Ft - Temperature Correction Factor ( from A7(g)) If the ambient temperature differ from 30C.
{Fg - Grouping Factor ( From A7(h) If more than one circuit}

Grouping Factor

Temperature Correction Factors

Power Factor Calculation

Voltage Drop Calculation

Example:- If Connect load is 6KW, 2 C PVC non-armoured cable cliped on wall, ambient temperature is 40 C and Power factor is 0.85.
 If Load is Single phase
Load Current Ic = Ic = P/V * p.f.  = 6000/1.732 * 0.85 = 30.6A

Circuit Break Size = 32A ( Next One Higher Value)

Cable Size = CB x 1.15 /Ft * Fg  = 32 * 1.15/0.87*0.85 ( From above Table the value of Ft and Fg )
                 = 49A
From A7(c) Cable Size = 2C x 10mm2 ( One next higher value)

Voltage Drop Calculation

               Ic x L x ( mV/A/m)
 Vd =   ----------------------

From Table A7(a) for 70 C Thermoplast PVC non-armoured Cable  "mV/A/m = 18"

So            30.1 x 22 x 18
    Vd = -------------------   = 7.9  so %age Vd = 7.9 /230 = 3.4 % ( which is less than 4% nominal Value)


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