Hello,
Dear All, i m new in this forum. plz kindly help me.
how can i calculate the or find the cable size ( in mm2 ) with cross sectional area.
kindly tell me the formula.....and little explain.
thank you all.....
best of luck.
"Bruqpa"
There are various methods. Commonly in Europe (assuming low voltage 400/230 V) there are tables published by the IEE and IEC which give the amount of current allowable in a cable for a given mm2. This also needs to be derated and various factors are given for temperature, installation method, etc.
In addition to ensuring the cable can carry the currently safely you normally need to consider the voltage drop induced by the cable and ensure that the cable is safe under fault conditions.
This site also has a cable size calculation tool (and there may be more information in the wiki):
http://www.myelectrical.com/pages/cables/cableSizing.aspx
hai
normallly cabe calculation done through the below formula
r = currentdensity X length of the conductor
area of the conductor.
for example
o.5sqmm cable have a current capacity of 4amps
current density valve varies depents upon type os material used for manufacturing the cable.
I agree with Steven and with the calculator results from the link. The standard IEC 60364:2001 is dedicated only for electrical installation in buildings-and that is very important of course.
Usually a low-voltage power cable conductor cross section has to be chosen according to these criteria:
1) Steady state current-maximum current possible for a prolonged long time.
2) Voltage drop for steady state current and for starting [induced motor starting].
3) Short-circuit current withstanding.
Steady-state current will heat the cable due to losses in cable resistance and the ambient medium-air or ground, for instance -will dissipate the heat cooling the cable.
The cables laying along or close to this cable will get a supplementary heating. The maximum conductor temperature is dictated by the conductor insulation type–for PVC is 70, for XLPE 90 degree C, for instance.
European standards as VDE 298 or IEC 60287 provide such information.
Voltage drop on cable impedance is important in order to calculate the remaining voltage on receiver terminals-as a motor for instance. In order to calculate this, one has to know the resistance and the reactance of the cable and the current and the power factor.
The standards will give the minimum voltage for steady state-for induction motor IEC 34-12 states the limits of this voltage connected with frequency drop. A usual value is 5% less than motor rated voltage.
For the start condition –even the voltage drop permitted will be more- the motor manufacturer has to be contacted or take this from catalog. The minimum permitted voltage at the start is less for small motor and more for large motor. Usually is 20% drop up to 5-10 HP and 10% for more than 100 HP.
In the case of short-circuit current- thermal stability- the conductor temperature could be more elevated [130 for PVC and 250 for XLPE].As the time is short no dissipation to the ambient is taken into consideration. The above mentioned calculator is very good for this purpose.