It's recommended that you use a timer only with the recommended characteristics for your pump. An average pool pump uses 3.5 kWh annually. Most timers, including the GE 24-Hour Indoor/Outdoor Mechanical Time Switch, are designed to withstand power in this range. If the instruction manual on your device does specify its usage with more powerful pumps, then you can go ahead and use it. If not, it's advised that you refrain from experimenting with your pump and timer. High voltages will cause the fuse to burn out or may lead to much more serious damage, such as a short circuit.