Answer / shridhar awasthi

Since it's an LT cable so in this case we can't apply the min cross sectional formula A=I square root t/K.

to find out the cross sectional area for this case fist find out the Load current which is given 26.01A. so refer the Manufacture cataloge and select the appropriate cable size for full Load current.
after selecting appropriate size of cable we will have to apply the derating factor according to the laying condition.
Now multiply that derating factor to cable ampacity,so we will get actual current carrying capacity of that cable.

Now for find our the no. of runs divide full load current to actual current capacity of cable after applying derating factor,so will get no. of runs.

now calculate voltage drop. if this in the permissible limit the our selection is right and if the V.d. is beyond the the increase the size of cross sectional area or no. of turns.
In this case 4 sqmm copper wire is sufficient for Star-delta starter.

Answer / wareagle

You don't have to calculate it. Just look it up in this
table. http://www.energy-
solutions.co.uk/cable_conductor.html
Looks like 4 mm^2 would do the job.

Answer / jinesh bhaskaran

we have to consider the type of motor starting, cable length and RPM of the motor.
According to these criteria we can select the cable from the cable manufacturer table.

can any one tell me the formula to select the thickness of wire selection according to ampere rating

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