Selection Of Cable And Cable Insulation

Selection Of Cable And Cable Insulation

Selection Of cable and cable Insulation

For better operation, working and increased life of cable depends on the insulation material used in the cable so proper choice of insulation material is having great importance.

Following properties are required in the insulation material:

1. Resistivity (ρ) should be as high as possible to avoid leakage current.
2. Its di-electric strength should be higher to avoid electrical break-down of cable.
3. High resistance to moisture so that it should not absorb moisture which protect the cable.
4. High thermal conductivity so that it passes out the heat to the next layer i.e. sheath.
5. High tensile strength to withstanding mechanical injuries while working with cables.
6. It should not get damaged or break.
7. It should be non-inflammable and fire proof.
8. It should be cheaper in cost.
9. It should be unaffected by chemical attack like acids/alkalies.
10. Copper, aluminium, tin are the most commonly used conducting materials in cables.
11. Choice of cross sectional area of cable conductors depends on various factors like.
12. Continuous load current.
13. Continuous rated current of cable.
14. Earth loop impedance.
15. Short circuit current rating.
16. Voltage drop across cable under steady state and transient condition.

Factors For Selection Of Cable

1. Larger operating temperature with high melting temperature.
2. High resistance to mechanical wear and tear
3. Lower effect of environmental condition and chemical attack.
4. Lower damaging effect of steady state and transient over voltages.
5. Should withstand freezing temperatures.
6. Longer life.
7. Less maintenance cost.
8. Conductors of cable should have low resistance so that voltage drop is less.
9. Temperature coefficient of conductor should be low.
10. Coefficient of expansion should be low.
11. High dielectric strength.
12. Low dielectric loss angle.
13. High insulation resistance.
14. Good flexibility.
15. Long service life.
16. Low flammability.
17. High resistance to ozone.
18. Good dimensional stability.

Proper Selection Of Cable :

1. Improve fire safety
2. Increased operational flexibility
3. Faster operations of fuses and circuit breakers.
4. Increased power quality.
5. High electromagnetic compatibility of the circuit.

Factors Of Cable Sizing

1. Ambient temperature.
2. Cable type and construction.
3. Cable conductor maximum operating temperature.
4. Derated cable current.
5. Motor static load in kw.
6. Motor static load power factor.
7. Motor static load running current.
8. Type of protection used like fuse, circuit breaker.
9. Large heat dissipation factor.
10. Cross section of conductor.
11. Standard cable sizes to be used as shown. below or design specified.