selection of conductor size of cable

Dear Sir,

I am a diploma Electrical Engineer working in power plant of ESSAR STEEL LTD.I would like to ask you a question.Question is
Which factors are considered for determine the size of cable conductor?

Thanking you
Regards

 

REFERENCE TO YOUR Q REGARDING CABLE SIZE COLCULATION .THERE ARE MANY FACTOR TO BE CONSIDER FOR EXP . 1. METHOD OF INSTALLATION. a) THERE ARE THREE TYPE OF COMMON WAYS .1) DRIECT LAID GROUND .2) RUN IN SINGAL WAY DUCT . 3) INSTALLED IN AIR. NO CABLE TRAY ECT. AS PER IEE REGULATION STATED
ACCEPTED VOLTAGE DRROP 4% FROM 415 VOLTS. 1/3 OF CURRENT THIS WILL BE CABLE SIZE. EXP. IF YOU HAVE 100 AMPERS CURRENT IN LINE THEN 35MM CABLE SIZE .THEN YOU HAVE CALCULATED Vd AS ABOVE.

 

[jbartos]

Suggestion: Consider
1. Voltage
2. Current
3. Nature of load, e.g. motor versus heater
4. Ambient temperature
5. Type of installation, e.g. in the air, underground
6. Number of conductors inside the cable
7. Frequency
8. Conductor temperature
9. Material, e.g. copper, aluminum
10. Length
11. Bending radius
12. Etc.

 

Regarding your question
you can return to the electrical stander tables like IEE or NEC tables to find the propor cable size for the certain load, distance, temperature and calbe material, otherwise you have to calculate depending on ohm's law and take into account some other factors like skin effect for a.c and the load behaivor.

Regards
Eng. Sermed al Saadi
sermedalsaadi@hotmail.com

 

[ambertec]

Please take a look at:

http://www.drzyzgula.org/bob/text/fr.tom/awg.txt

There is a really very nice wire table there with much of the information you need.

Good luck.

John Dunn
ambertec@ieee.org

 

[redtrumpet]

I recommend preparing a design criteria before embarking on cable sizing. I have supervised too many designers who simply look in the table in the Code without thinking about the factors that go into cable selection and sizing. By preparing a design criteria, you are forced to think of the factors you should consider.

The design criteria would normally include the items jbartos mentions, but some other things to think about:

1. Using the next-larger size cable. Often the cost is minimal, but is repaid with lower copper losses (higher efficiency) and increased equipment life because of reduced operating temperature.

2. Equipment terminal temperature rating. Sizing a cable based on 90 C operating temp does no good if the equipment lugs are rated 75 C.

3. Emergency overload capability. On some feeders you can "cheat" a little on the sizing if there is a definite overload condition anticipated. For example, XLPE insulation is normally rated for 90 C, but can operate at 130 C for a period usually defined as not exceeding 100 hours per year and no more than five overload periods in the cable's lifetime. By using 130 C instead of 90 C for sizing the cable under overload conditions, you can use a smaller cable, a useful cost-saving measure when dealing with MV systems and larger kcmil sizes.

4. System grounding and protective relaying will affect voltage insulation level, especially above 5 kV.