Sir , I found a good web, from that web we can select proper wire with temperature estimate by knowing resistance of wire.
http://circuitcalculator.com/wordpress/2007/09/20/wire-parameter-calculator/
E.g. According to that web, If I get 12 AWG copper wire for 20 A , and if I measure resistance of that wire than we can know temperature of wire, in other language loss of heat.