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My relative's house is very old (built in 1920s or 1930s) and has several 2-prong outlets with no ground. The screw in the center is not grounded either.

I would like to be able to use modern equipment (requiring 3-prong outlets) safely. What should I do?

Edit: Would an isolation transformer help?

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    Can you get us a photo of the inside of a representative receptacle box please? – ThreePhaseEel Nov 29 '16 at 2:17
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Well the most obvious and always recommended answer is to upgrade the old electrical wiring. Very old wires can have insulation falling off or crumbling if you try to start working with it. For a very old installation that may also involve replacing the electrical distribution box (panel) as well.

Now with that said there is not anything inherently unsafe with a two wire system as long as common sense is used. That common sense has to include:

  1. Not using electrical appliances when the user could be providing an alternate path to GND for the AC electrical power. I.E. do not stand in a full bathtub and drop a plugged in hair dryer into the tub).
  2. Use double insulated electrical tools if at all possible.
  3. Do not use electrical appliances that have frayed power cords.
  4. Replacing the two wire outlets with a GFCI that can trip if the hot wire current is not equal to the neutral wire current. GFCIs used in this configuration need to be labeled as not providing a safety GND connection.
  5. Consider testing the existing wiring (or get an electrician to do it) to see if the old neutral wiring creates a voltage drop of more than a couple of volts when circuits are loaded. If higher voltages are seen then use of bare metal appliances such as a desktop computer chassis may expose you to the voltage drop of the existing wiring. If this is the case the only real solution for safety is to get rewiring done.

For the outlet with the reversed polarity the first thing that should be done is to replace it with one wired to the correct polarity. Another thing to look at is to replace outlets with the newer style where the slot for the neutral prong is larger than the hot wire prong.

  • Although this advice is absolutely sound, if you start touching the wiring/replacing outlets then the OP is going to quickly discover why it's strongly recommended to replace old wiring: As soon as you disturb it, the insulation will begin crumbling and falling off the wire, leaving exposed conductors. OP - if the house wiring is that old, please encourage a replacement programme - it will be expensive and hard work, but it's difficult to exaggerate the danger of very old wiring ESPECIALLY if you begin disturbing it in any way. – Dan Nov 29 '16 at 14:13
  • @Dan - I fully agree with you. That is why the very first part of my answer says that the most obvious thing to do is to replace the wiring. I'll modify that some to state that the replacement is highly recommended. – Michael Karas Nov 29 '16 at 14:28
  • @Dan: the problem is that my 86-year-old grandfather lives in the house, and I don't know if he could handle the stress of having his house torn apart. He just lost his wife (my grandmother) too, so I don't think this would be a good time. – Demi Nov 30 '16 at 3:54
  • @Demi Completely understand, bud - in which case the second best answer is to simply not touch any of the wiring at all for now or at least engage an electrician to do so. – Dan Nov 30 '16 at 9:35
  • @Dan Is it okay to just use an isolation transformer between the wall outlet and whatever it is powering? – Demi Dec 1 '16 at 4:38
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Generally, a 3-prong outlets work on 2-wire installation just as well. The 2-wire installation is bound to have one of the wires grounded (the neutral), so the grounding prong is just connected to the neutral, together with one of power prongs. The key is choosing the correct one!. The only thing you lose on 2-wire instalation is the option to install a central GFCI.

Now, the legality of replacing 2-prong sockets with a 3-prong ones depends on local code, and that's why you should call a licensed electrician. If the operation is possible, it won't be expensive as it's merely replacing a few sockets. A licensed electrician will know if such retrofit is possible without any extra conditions, on condition that the new sockets have integrated GFCI or not possible at all in your installation.

//edit: Please do not change the meaning of my post. The first part is not an advice, it's merely a summary on how installations were done in pre-GFCI times. The only advice here is to hire a licensed electrician.

  • The purpose of comments is to suggest improvements to answers. Obviously, having considered mine, you are happy with your answer. I have tidied up my comments as per comments are disposable and when should comments be deleted – RedGrittyBrick Nov 29 '16 at 22:08
  • @RedGrittyBrick You commented about 2 issues: the reversal and unsafety. I am not happy with my answer because I don't understand how whose issues are relevant to my answer. I still would like to learn more about your concerns. – Agent_L Nov 30 '16 at 9:50

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