Two-prong receptacles, often found by an inspector in an older home, that are connected to two-wire cables do not have the ground wires, which protect people and electrical devices in case of a ground fault. It is possible to retrofit a new three-prong or GFCI receptacle into the same receptacle box without any rewiring, as long as the box itself is grounded.
Metal boxes attached to armored, or BX, cable, which is a type of wiring commonly found in old homes, are typically found to be properly grounded. The armored or BX cable’s flexible metal jacket serves the same purpose as a dedicated ground wire.
If the box is not grounded, a GFCI can be installed or an electrician can be hired to fix the wiring.
The image above is a GFCI that was installed to replace the old, 2-prong ungrounded wall receptacle in an older home. This GFCI must be labeled as a GFCI without an equipment ground.
Simply replacing an older 2-prong outlet with a 3-prong outlet can be hazardous, because the receptacle will appear to be functional with a ground, but in fact there isn’t one. If someone were to plug a faulty 3-prong device into that “fake” grounded receptacle, a shock hazard is very likely. Electricity moving through the device casing would create an energized surface from which a person could be electrocuted.
Another problem with replacing ungrounded 2-prong receptacles with 3-prong one is in relation to surge-protection device, which relies on a solid ground to route any transient activity. The ungrounded receptacle would not be able to protect the device from a surge.
It is permissible to replace a 2-prong ungrounded outlet with a 3-prong GFCI outlet, but it must be labeled as “GFCI Protected Outlet, No Equipment Ground.” Even though there is not a grounding conductor, there is still some protection against shock provided by the GFCI.
The bottom line is, play it safe. To do electrical receptacle upgrades in a manner that will provide the most protection to the inhabitants of the home, have a licensed electrician who has the proper equipment and knowledge to do it right make the upgrades.
Scott Price, CPI, #1532
Certified Home Inspector
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