- Q. How about upgrading old two-prong ungrounded outlets from the ’70s and back?
A. Upgrading outlets from two-prong to three-prong is allowed by code only if the circuit is GFCI protected. If you do add grounding-type receptacles to an ungrounded circuit, you must not wrap any ground wire around the grounding terminal on the new receptacle. Any GFCI without an attached ground wire must be marked "No equipment ground." Also, any GFCI-protected outlet without an attached ground wire must be marked "GFCI protected. No equipment ground."
To upgrade a two-wire system, you can either replace all of the breakers in the panel with GFCI breakers, or place a GFCI feed-through outlet at each home run location. Although breakers are expensive, locating the home run outlet in each circuit can be time consuming. Using breakers is a labor-saving and reliable approach.