Can you change an existing two prong outlet to a new three prong outlet? A two prong receptacle is an ungrounded device. To replace a two prong with a new three prong receptacle, a ground wire must be available for grounding. Many unqualified electricians violate this code requirement. An ungrounded device does not provide a path for ground faults causing the possibility of unwanted metallic appliances becoming energized. Note: You can replace a two prong device with a GFCI. The device must be marked