WAZIPOINT Engineering Science & Technology: Electrical Power Cable Short Circuit Current Capacity

## How Calculate Cable Short Circuit Current from Short Circuit Current from Table?

You may find the short circuit current for a particular type of cable for a specified period of time from your cable manufacturer’s provided catalogue. For example the below table is showing different sizes from 16 square mili-meter to 2500 square mili-meter of cable in first left column and time duration from 0.1 second to 5 second in next 10 columns.

Table: Typical short circuit current (kA)
 CSA (sqmm) Duration in Second 0.1 0.2 0.3 0.4 0.5 1.0 2.0 3.0 4.0 5.0 16 7.2 5.1 4.2 3.6 3.2 2.3 1.6 1.3 1.1 1.02 25 11.3 8 6.5 5.7 5.1 3.6 2.5 2.1 1.8 1.6 35 15.8 11.2 9.1 7.9 7.1 5 3.5 2.9 2.5 2.24 50 22.6 16 13.1 11.3 10.1 7.2 5.1 4.1 3.6 3.2 70 31.7 22.4 18.3 15.8 14.2 10 7.1 5.8 5 4.5 95 43 30.4 24.8 21.5 19.2 13.6 9.6 7.8 6.8 6.1 120 54.3 38.4 31.3 27.1 24.3 17.2 12.1 9.9 8.6 7.7 150 67.8 48 39.2 33.9 30.3 21.5 15.2 12.4 10.7 9.6 185 83.7 59.2 48.3 41.8 37.4 26.5 18.7 15.3 13.2 11.8 240 108.5 76.7 62.7 54.3 48.5 34.3 24.3 19.8 17.2 15.3 300 135.7 95.9 78.3 67.8 60.7 42.9 30.3 24.8 21.5 19.2 400 180.9 127.9 104.4 90.4 80.9 57.2 40.4 33 28.6 25.6 500 226.1 159.9 130.5 113.1 101.1 71.5 50.6 41.3 35.8 32 630 284.9 201.4 164.5 142.4 127.4 90.1 63.7 52.0 45.0 40.3 800 361.8 255.8 208.9 180.9 161.8 114.4 80.9 66 57.2 51.2 1000 452.2 319.8 261.1 226.1 202.2 143 101.1 82.6 71.5 64 1200 542.6 383.7 313.3 271.3 242.7 171.6 121.3 99.1 85.8 76.7 1600 723.5 511.6 417.7 361.8 323.6 228.8 161.8 132.1 114.4 102.3 2000 904.4 639.5 522.2 452.2 404.5 286 202.2 165.1 143 127.9 2500 1130.5 799.4 652.7 565.3 505.6 357 252.8 206.4 178.8 159.9

Here is some limitation is that only some particular times are mentioned; say 1 second then 2 second. But if you need short circuit current for 1.5 second or 1.75 second for a particular size of cable that you cannot find from your short circuit current table. In this situation as a cable engineer you must calculate the short circuit current for desired period of time.

Before going to calculate the short circuit current we need to keep in mind some basic point about short circuit current. Short circuit current table give the value for particular type of cable conductor and screen based on some conditions, like-

•      Short circuit starts from the maximum operating
temperature of cable        conductor/screen;
•    Maximum temperature during short circuit;
•    Maximum short circuit current duration is 5 seconds.

Now, come to the main point: if the short circuit current is required at duration not mentioned in the catalogue what we asked before. Then we need to obtain by dividing the short circuit current for 1 second by the square root of the required duration.

### How Calculate Cable Short Circuit Current

First of all we need to know the short circuit current for 1 second and the duration of time. Then we can calculate short circuit current for that time duration.

Let follow the formula for cable short circuit current calculation:

Where
Isct= Short circuit current for t second in kA
Isc1= Short circuit current for 1 second in kA
t = Duration of time in second.
kA- Kilo-Ampere.

For example:
What is the short circuit current for 3.5 second for 2500 sqmm cable?

Solution:
Given time duration is 3.5 second,
Short circuit current for 1 second is 357 kA;

So, Isct = 357/(P3.5)= 190.83 kA