I have read How do I use three-prong appliances when my outlets are mostly two-prong?.

I have recently moved into a house that has some two-prong and some three-prong outlets.

The place in the kitchen where the refrigerator fits has a two-prong outlet. The house had no refrigerator in it when we moved in. When the new refrigerator was delivered, the delivery person said to go to the DIY store and buy a little adapter. The first couple of days, I ran a heavy duty extension cord over to a three-prong outlet, but when I had time to go buy some adapters, I switched to that method, because I was concerned about the cord being a tripping hazard, as it had to cross the kitchen floor right where the door to the basement and garage opens.

We also have a microwave oven, a chest freezer, and a computer running on adapters. They are all on different circuits except the microwave and the fridge which share a circuit. I know this because yesterday we mapped the circuits by turning on all the lights and then flipping the circuits one at a time and observing the results.

We are planning to resolve the problem at some point. How quickly should we do that? Within one week or one month?

  • 3
    Are there any GFCI protective devices in this house? Or is this full-on 1953? Sep 12, 2019 at 4:01
  • 1
    Can you get us some photos of the breaker panel? Sep 12, 2019 at 4:13
  • @ThreePhaseEel - I will try to do that tomorrow. Sep 12, 2019 at 4:48
  • @Harper - I haven't found any outlets with the little red button. However, there are some special outlets in the two upstairs bedrooms that have six places to plug something in (built in). Sep 12, 2019 at 4:49
  • 2
    Have you checked that the 3-prong outlets actually have a ground connection? That seems like the sort of thing that's worth checking. Sep 12, 2019 at 6:34

1 Answer 1


For older appliances and such, pre-electronics, it's only a safety issue and even then, only under the worst case scenarios. The National Electric Code is all about those worst case scenarios however, hence the requirement. I'm not minimizing the safety aspect, I'm just saying that people survived for a LONG time with 2 prong outlets.

That said, the OTHER issue (which was not really an issue when the change was made) is that electronics, or more specifically anything that uses a "Switch Mode Power Supply" (SMPS), needs to have a solid reference to ground so that it can deal with what's called "Common Mode Noise" created by the power supply itself. Now virtually EVERYTHING you see with any sort of electronics in is has a little SMPS, all of them creating CM noise on the line. With no reference to ground, that noise builds up, potentially degrading the life of your electronics. So the longer you wait to fix it, the shorter the life of your computers, TVs, phones, "smart" appliances etc.

But per that other thread, in a lot of cases, older houses were wired with what's called "BX" cable; flexible metal covered conductors, and that was grounded, then the outlet and switch boxes were steel as well, all connected together. So if that's what you have, AND you have a metal screw (not plastic as they are now) holding the cover plate on, you WILL get a ground connection by using those adapters and attaching them via that metal screw.

Here is a better thread illustrating this concept.

What is the purpose of the "grounding" tab/wire on a 3-prong to 2-prong adapter?

  • Most switching power supply's for phones and small loads are 2 prong not 3. A high neutral voltage can cause problems because of the harmonics created by switching supplies. An NEC approved method is to add a GFCI , then 3 prong outlets can be added but must be labeled “GFCI protected no equipment ground” many homes built prior to the early 70’s have this setup as adding a new separate grounding wire was not legal until recently and it won’t shorten the life of the supply.
    – Ed Beal
    Sep 12, 2019 at 14:36
  • Yeah, agreed with @EdBeal, your comments about SMPSs needing ground are not true. It depends on the design of the SMPS, but there are many that do not need or use a ground connection, and they work fine. And those that do use ground are generally using it to avoid radiating too much EMI for regulatory purposes, and won't be damaged if it's missing (such as if it's plugged into a non-grounded GFCI, which is perfectly legal).
    – Nate S.
    Sep 12, 2019 at 16:25
  • FYI - Microwaves and refrigerators are not very compatible if they are on the same circuit. They have a tendency to make circuit breakers trip when they are paired up. You might want to put them on different circuits. Sep 12, 2019 at 19:32
  • Well, when I plugged in the adapters I bought, I ignored the little metal loop. Now I see that I should install them properly by unscrewing the screw, placing the adapter with the correct orientation, and then putting the screw back in. (I checked, and the screws are metal.) // What about the power strip with the built-in switch that I use to plug in my computer, monitor, printer, portable phone? How does that play in to all of this? Or should I ask a new question about that? Sep 12, 2019 at 21:45

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