Concessional duty rate for electrical insulators excludes paper-based insulated items; excess excise duty thereby exempted. Concessional excise treatment is provided for electrical insulators other than paper or paperboard insulators coated, impregnated or covered with plastics, by exempting so much of the duty specified in the Tariff Schedule as exceeds the amount calculated at a fifteen per cent ad valorem rate, under the executive power to grant exemptions in the public interest.