Nearly every older home I inspect contains several ungrounded three-prong receptacles (outlets). Older two-prong receptacles are ungrounded, but modern three-prong receptacles are designed to be grounded for added protection. The small third hole in a three-prong receptacle is for the ground.
The primary reason for ungrounded three-prong receptacles in older homes is that the electrician or other person who upgraded the outlets used the wiring already present to make the installation much easier. Often times the existing wiring is older knob and tube, which does not possess a grounding conductor, so the installer simply uses the available hot and neutral wires. The end result of this improper “upgrade” is newer outlets that look better and will accept a three-pronged plug but provide no real benefit over their older two-prong predecessors since they offer no additional protection.
Many homeowners seeking to upgrade their wiring request that older two-prong receptacles be upgraded to modern three-prongs, but they have no idea once the work is finished that their new “grounded” receptacles are actually not grounded. In fact, many homeowners aren’t even aware that grounding is the primary difference between newer and older receptacles. Without this knowledge, they hire someone to perform an electrical upgrade, think the work looks fine, trust that everything has been done properly, and have no idea that the “upgrade” they paid for is subpar.
Now, two-prong ungrounded receptacles still exist in many homes and often pose no problems. This is because over-current protection devices (circuit breakers and fuses) are designed to trip or blow if an over-current occurs. However, these devices can fail, which is why grounded receptacles were invented to provide additional protection to people and electrical devices if a fault occurs. Having additional protection is certainly a good thing, so you do want your three-prong outlets to actually be grounded.
If you’re looking to have older two-prong receptacles upgraded, be sure to hire a qualified and reputable electrician, and make it a point to stress that you want your new three-prong outlets to actually be grounded as they should. Upon completion of the job, ask the electrician to verify (by showing you with a tester) that the outlets are, in fact, grounded as they should be. You’ll likely pay more to have the job done properly, but you won’t regret it.
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