The third prong on an electrical plug is for the ground wire, which further protects electrical components. When conditions are operating as intended, the ground wire should never have any electrical current. Comparing it to the shoulder on a roadway. When your car is running as it should, the shoulder is not needed, but when something goes wrong, it is necessary to pull over for safety. If a three-prong outlet is installed with only two wires and no ground, it's considered an ungrounded three-prong outlet. This defect can often be found in older houses, and sometimes newer homes that have been improperly wired. This increases the potential for shocks or electrocution and prevents surge protectors from properly doing their job, possibly damaging electronic components. Two-prong outlets should never be replaced with a three prong outlet and leave the ground or third-prong unwired.
The National Electrical Code (NEC) Section 406.4(D)(1) states that if a grounding path exists, it needs to be used. Ground paths have been required in homes since 1962. In a home built after 1962, the only acceptable repair for an ungrounded outlet is to ground the outlet. Moreover, homes built before 1962 can and should be brought up to code for safety reasons. The following are potential options for correcting an ungrounded three-prong outlet.
1. Install a two-prong outlet. Two-prong outlets are allowable and clearly indicate the outlet is not grounded. However, if someone wants or needs to use a device requiring a three-prong outlet, they will likely utilize a three-prong adapter. Which is not the safest option. Three-prong adapters are only intended to be used with properly grounded two-prong outlets.
2. Install a Ground-Fault Circuit Interrupter (GFCI) outlet. The GFCI is a fast-acting circuit breaker designed to shut off electric power during a ground fault within as little as 1/40 of a second. A GFCI outlet will help to prevent electrocution, though it will not help surge protectors do their job. If this option is employed, the outlet should be identified with a sticker on the face of the GFCI outlet that says “No Equipment Ground.”
3. Install a standard three-prong outlet and add Ground-Fault Circuit Interrupter (GFCI) protection to the circuit. GFCI protection can be installed at the breaker panel, or somewhere between the breaker panel and the outlet. When using this option, labels must be applied to the outlet that indicates “GFCI Protected” and “No Equipment Ground.”
4. Upgrade your house wiring with a ground wire and install three-prong outlets. A qualified electrician can run a ground wire from the main electrical box if there is access. They may fish a ground wire to each outlet without opening up walls, or, if the house was wired with armored cable, the outer metal sheath can be used to ground the outlets. However, the rewiring option will likely be the most intrusive and costly.
Ultimately, homewoners can employ the services of a certified Home Inspector to test, inspect, and report findings of the home wiring before employing the services of an electrician, if needed.