We have all seen and most likely used these adapters. Here is the situation. You live in an older home that has two-prong outlets and you need to plug in a cord that has three prongs. What do you do? Well, you could hire an electrician to change out or re-wire the outlet. Then you go to your local big box home improvement store and see one of these little babies. You say to yourself….Self, this thing is cheap and it solves my problem!
Is your problem solved?
Maybe, maybe not. If your home was built in the 50’s or later (and you have two-prong outlets) then you may actually have grounded wiring in your home. If this is the case then the answer is yes it does solve your problem. There is a condition though. See that little green tab on the adapter? It MUST be attached to the screw on the cover-plate of the outlet to provide a ground connection. Once this is connected, it is completely safe to plug in a three-prong cord. If you do not have grounded wiring in your home, then no you should not use this type of adapter.
How do I know if I have grounded wiring?
You can remove the cover-plate on the outlet (turn off the breaker first) and simply look into the outlet box to see if there is a bare copper wire attached to the metal box and/or the green screw on the outlet. You can also use a pig tail tester to verify a ground connection from the Hot side (smaller hole on the outlet) to the cover-plate screw. This is an very inexpensive tester available a most home improvement stores. If you are not comfortable doing this, call an electrician to verify it for you.
As in many cases, there is an exception and here it is. If your home is wired using an old armored cable (AC) commonly called BX cable, the tester will show that you have a ground connection. This cable has a metal spiral outer casing. The problem is that unless this cable has a bond strip you cannot use the outer casing as a ground and cannot use this two-prong adapter. If you do, a ground fault can essentially turn the metal spiral wrap into a heating element in your walls which obviously is a fire hazard. Also be aware that you cannot “upgrade” to a grounded three-prong connector on this type of circuit as it creates the same hazard. If the bond strip is present then yes, you can use the two-prong adapter given that you connect the tab to the cover-plate screw. This bond strip is not always easily visible and should be verified by a licensed electrician if you are unsure.