This Technical Specification is applicable to industrial electroheating installations using electric energy as input, alone or in combination with other kinds of energy.However,external combustible fuel energy input is not dealt with, and all considerations begin at the electric only mains frequency source to which the installation is connected. Any external voltage transformation from the supply network to the plant into a special voltage which is fed into the installation is not dealt with in this Technical Specification, since it is not considered a responsibility of the manufacturer of the installation.