The magnetic flux has to change its direction at butt-joint meanwhile at butt-joint occur the hot spot. The hot spot can be measure using thermistor in term gradient temperature. These papers describe the result of measurement and evaluate the localized loss of 100 kVA 3phase distribution transformer assembled with the mix 60- 45° in different layers of T-joint core. Methodology that is used in this investigation is measurement of localized loss in the transformer core using no load test by arrays of thermistor on the surface of Cold-Rolled Grain Oriented (CRGO) material of transformer core lamination. The measurement involves the variation of temperature rise at each location measurement. From the result of this investigation that is the localised power loss at the outer edge of the mix 60-45° in different layers of T-joint core of three phase core is 1.22 W kg-1 and rises to be 1.72 W kg-1 at the inner edge of yoke when the transformer core energized 1.5 T 50 Hz. The localised power loss at the overlap area of the mix 60-45° in different layers of T-joint core is 1.72 W kg-1 and decreases to be 1.44 W kg-1 at the outer edge of middle limb when the transformer core energized 1.5 T 50 Hz. The several harmful effects can occur because the flux flows out of the rolling direction.