Fuses blow. Is it ALWAYS an issue on power board.

No. Any shorted electronic component (or loose wire for example) can potentially cause a fuse to blow. A short circuit means that the power supply will be forced to supply a maximum amount of current (amperage) which will exceed a fuse's current maximum rating. Once that maximum rating has been exceeded the fuse will blow to prevent such incidents like fires starting. The fuse, like the breakers in your house, aren't necessarily there to protect your electronic/electrical devices.