The NEMA 1-15P Standard does not utilize a ground, the equipment that uses this plug most likely has a double insulated casing that has been approved by NEMA and other applicable safety agencies to not require an electrical ground. In the past, the NEMA 1-15P was the standard plug type, but in recent years it has been replaced by the NEMA 5-15P for safety reasons for electrical devices that do not have additional grounding precautions internally.