The purpose of the over current protection device is to limit the amount of current the USB port can draw, such as in a short circuit situation. It should not, however be design to function as a current cop when the downstream device power consumption reaches near the allowable port limits given its declared power requirement. The sizing of the over current protection device should be chosen mainly to protect user safety and against property damage. Over current protection should not be used to enforce the current limits (500mA) that USB devices are required to meet.