HT Cable Sizing

Huh?

I have in the past done LT calculations involving transformer and cable impedance (size versus length) to determine maximum fault current.

I doubt that any cable would ever be sized to handle such large currents; instead, what you are sizing are fuses or circuit breakers and their required interrupting capacity.

Hi Friends,

In LV or MV, we are considering short circuit current. About 40 years ago, when I just joined electrical field, my supervisor told me that the first 10 meters of LV cables from MCCB are not protected against short circuit because of economical reason.

If you consider the short circuit currents, your cables would be quite large.

However, technology changed, most of MCCBs or MCBs now are current limiting, and possible to protect the connected LV cables against short circuit.

So you must make sure your LV cable is protected by your current limiting MCCB.

Regards

yes i agree it is for both LT and HT cable sizing but in HT it is mandatory.Why is so in HT ?

Dear all,

BS7671 (IEE), 430.3 states "A protective device shall be provided to break any overcurrent in the circuit conductors before such a current could cause a danger due to thermal or........, NOTE: An overcurrent may be an overload current or a fault current."

IEE is for LV installation, and circuit conductors must be protected against a short circuit current. This is mandatory in LV.

Regards

It needs to be considered in both cases. Why "we" are "not" doing it is the imponderable.

British Standard 7671 again?