In current carrying conductors, if the radius of the conductor is less than the critical radius, then addition of electrical insulation is desirable, as (IES-95)
(a) it reduces the heat loss from the conductor and thereby enables the conductor to carry a higher current.
(b) it increases the heat loss from the conductor and thereby enales the conductor to carry a higher current.
(c) it increases the thermal resistance of the insulation and thereby enables the conductor to carry a higher current.
(d) It reduces the thermal resistance of the insulation and thereby enables the conductor to carry a higher current.