Earthing system TN and IT, design

Simplified method 3: Table

In this method, the value of the short-circuit current is known at one end of a feeder (cable). The table will give the value of the short-circuit current à the other end of the feeder.

  • The top part of the table is for the copper wires:

    • Right column is the cross section

    • The contents is the length of the wire.

  • The bottom part of the table is the same for Aluminum wires

  • The central part is the short circuit current value.

    • The right column is the short circuit value at the start of the cable (known value)

    • The center is the short circuit value at the end of the cable.

ExampleShort circuit value of the current Isc

In our example, the cable is made in copper with a cross section of 47,5 mm2 and a length of 20 m. The short circuit value at the start of the cable is estimated at 28 kA

On the top part of the table we select the row corresponding at 47,5 mm2 copper cross section. We select after the column with the length of 20m

On the center part of the table, we select the row corresponding to the short circuit value at the start of the cable.

At the intersection of the column and the row, we have the value of the estimated short circuit at the end of the cable, here 14,7 kA!

PreviousPreviousNextNext
HomepageHomepagePrintPrintCreated with Scenari (new window)