At present, Power Distribution Blocks, eg. the Fuse Block (F/B), distribute power sources to all loads via Auto Fuses. However, with recent trends favouring miniaturization, Mini Auto Fuses will replace the larger standard Auto fuse. If the F/B is miniaturized to use Mini Auto Fuses, and the distance between fuses is decreased, a heat problem will occur. Several experiments have been carried out in an attempt to analyse this heat problem, their purpose being to estimate the temperature rise of each fuse in the proposed F/B, to aid in its design. The fuse is considered as a heat source, and the F/B as a combination of these heat sources. The temperature of each fuse is determined by its own temperature and the Heat Interference (Heat Radiation) of the other fuses. With this in mind, experiments on Heat Interference of Mini Auto Fuses were carried out. As a result of these, an expression was developed, and a program was written based on this expression. This enabled the calculation of each fuse's temperature after heat interference by inputting the matrix of the number fuses, the distance between the fuses, and the individual fuse's temperature rise. In this way, it was calculated that, by changing from standard auto fuses to mini auto fuses, the distance between the fuses can be reduced by 30%.