What is Tinning?

Tinning :

"Copper and rubber, when brought into connect, react upon one another chemically. It was formerly thought that this action was due entirely to the sulfur in the rubber compound combining with the copper. Pure rubber, however, also reacts with the copper.
Coating the copper with tin or an alloy of tin affords the necessary protection. Tinned copper wires have been used for wiring and flexible cables.
Solid conductors have round circullar or square shape. The term protection is used to cover protection against mechanical damage, chemical or fire etc.
A term tinning is used is cables and conductors. Tinning means copper has a deleterious effect on rubber therefore tinning is used in each wire of the conductor of V.R>I cable. When we use P.V.C insulation on copper conductor, the copper conductors need not be tinned because there is no chemical effect between the P.V.C and bare conductor.