Applicability of depreciation rates of electricity act,2003g

I want to know the applicability  of Depreciation Rates mentioned in Electricity Act, 2003.

There are three electricity companies and all are under implementation stage and not yet started production or generation of electricity. So i am confused that Depreciation rates of "Electricity Act, 2003" are applicable or Depreciation rates of "Companies Act, 1956" are applicable. All the three companies are unlisted and Non-SSI.

Also there is one more company which is "Holding Company" of above three companies. This company is not meant for production or generation of electricity, this company is just giving its administrative services to its subsidiary companies .So whether Depreciation rates of "Electricity Act,2003" are applicable to Holding Company as well.

As per my search in india some companies are following Depreciation rates of "Electricity Act,2003" and some companies are following Depreciation rates of "Companies Act, 1956".