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Converting Two-Prong Outlets

By In two-prong outlets On January 17, 2009


A common question I get about older homes is whether two-prong outlets can safely be changed over to three-prong outlets.  Most home buyers today don’t want to be stuck with two-prong outlets throughout the house.  Two-prong outlets can always be changed to three-prong, and this can be accomplished a few different ways.  Today I’ll give a very brief explanation of what the third prong is for, and I’ll discuss a few ways to convert to a three prong outlet.  I didn’t consult an attorney before writing this article, so I feel like I should add a disclaimer before giving any electrical how-to advice:

Don’t do any of this work if you’re not qualified – you could start a fire or get electrocuted.  This is not a comprehensive how-to guide; this is only an overview.

The third prong on an outlet is commonly referred to as ‘the ground’, and it provides an alternate path for electricity that may stray from an appliance or product.  This is an important safety feature that has been required since about 1962.  This minimizes the risk of electric shock, and allows surge protectors to protect your electrical equipment, such as televisions, computers, stereos, and other devices.

The best way to upgrade a two-prong outlet is to install a three-prong outlet that has a continuous electrical path back to the panel.  If the outlet is installed in a metal box, and that metal box has metal conduit all the way back to the panel, this will probably be easy to do.  To test this, you can use an inexpensive pig-tail electrical tester, which is available at any hardware store for about two to three dollars.  With the circuit energized, touch one end of the tester to the hot wire, which should go to the smaller slot on the outlet, and one end of the tester to the electrical box  (see photo below left).  If the tester lights up, the box is grounded.  Now all you need to do is attach a bare copper wire to the box, and use this as the ground wire for a three prong outlet (see photo below right).

Testing For Ground on a Two-Prong Outlet  Grounding a three-prong outlet to a box

If you perform the test with a pig-tail tester and the light doesn’t light up when you touch the hot wire to the box, the box is not grounded (or you’re not touching a hot wire).  In this case, you could run a ground wire back to the panel, or you could replace your two-prong outlet with a GFCI outlet.  A GFCI outlet provides protection against electrocution, but without a ground wire, this outlet won’t provide any protection for your electrical equipment.  A surge protector plugged in to an ungrounded outlet will do nothing, and you could fry your new plasma TV.

Testing for ground at a cover plate

What about two-prong to three-prong adapters?  These can only be safely used on a grounded two-prong outlet.  A pig-tail tester will light up on a grounded two-prong outlet if you touch one lead to the smaller slot on the outlet, and the other lead to the screw in the middle of the outlet.

Unsafe Adapter Use Safe Adapter Use

If this is the case, you can safely use a two-prong to three-prong adapter, as long as you secure it to the outlet with the cover plate screw.  Any other use of a two-prong adapter is unsafe.

Reuben Saltzman, Structure Tech Home Inspections – Email – Minneapolis Home Inspections

        



About the Author

Reuben

Reuben is a second generation home inspector with a passion for his work. He grew up remodeling homes and learning about carpentry since he was old enough to hold a hammer. Reuben has worked for Structure Tech since it was purchased by Neil in 1997, and is now co-owner of the company. Reuben’s favorite customers are the ones who have a lot of questions; he grew up thinking he was going to be a school teacher because he enjoyed teaching others so much. In a sense, that’s a lot of what home inspections are about, so Reuben truly does what he loves. Reuben has an A.A. degree in liberal arts and has attended most of the Building Inspection Technology classes at North Hennepin Community College. Reuben and his wife are the proud parents of two young childen, Cy Alexander and Lucy Nicole, and have a German Shepherd named Stanley. With two young children Reuben doesn’t have much free time, but he still tries to play disc golf as often as possible during the summer. Reuben lives in Maple Grove, MN. Professional Qualifications / Memberships: *ASHI Certified Inspector *President, ASHI Heartland Chapter *Member, Minnesota Society of Housing Inspectors (MSHI) *Licensed Minneapolis Truth-in-Sale of Housing Evaluator *Licensed Saint Paul Truth-in-Sale of Housing Evaluator *Licensed Maplewood Truth-in-Sale of Housing Evaluator *Licensed Hopkins Truth-in-Housing Evaluator *Licensed Robbinsdale Point of Sale Evaluator *Affiliate Member, Southern Twin Cities Association of Realtors

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32 Comments

  • Reuben Saltzman 1 YEAR AGO

    @Terry - if the box were grounded, the self grounding outlet would also be grounded, assuming you're using a self-grounding outlet. First, determine if your box is grounded. If not, the correction would be to re-wire the outlet.

  • Terry Exler 1 YEAR AGO

    Hi Reuben thanks for the info. I have replaced 5x 2 prong double power outlets in our old farm house. All the new 3 prong outlets have a metal strip at the back (which I was told helps with grounding), We have a black and a white wire in the box, no ground wire. I was told if you screw it onto the box properly it will be grounded & 2x of them are, 3x are showing open ground used a 3 prong tester. I've gone back twice to make sure it was all connected ok. How else can I fix this? Is it a matter of sanding back some metal on the box (seems to be a bit of oxidation) And yes I have only 2 wires to attach to the outlet not 4 and no ground wire..

  • Terry Griffin 1 YEAR AGO

    Thanks for the informative article and even more informative answers to questions. My house was built in 1952 and the original 3 unremodeled rooms have ungrounded 2-wire connections. My question is whether it is legal to run a single wire ground independent of the original wiring back to the ground bar on the main panel?

    • Reuben Saltzman 1 YEAR AGO

      Hi Terry, No, it's not legal to run a separate ground. It was acceptable at one time, but not any more.

  • Yui 1 YEAR AGO

    Is there another way to run the 3rd prong to a ground such as the earth? Thanks.

  • Ted 2 YEARS AGO

    About 20 years ago I worked for an electrician and we converted a house from 2 prong to 3 prong outlets by running a jumper from the neutral white screw to the mechanical green grounding screw on the outlet. Is this acceptable? We made sure the polarity was correct on the system prior to doing this.

    • Reuben Saltzman 2 YEARS AGO

      Hi Ted, No, that wouldn't be acceptable. There is no separate path for the current to travel back to the panel.

  • Reuben Saltzman 2 YEARS AGO

    Mark - if it's a 15 amp circuit, use 14 gauge wire. If it's a 20 amp circuit, use 12 gauge wire. Solid or stranded is fine, sheathed or unsheathed is acceptable... but you obviously wouldn't use unsheathed stranded.

  • Mark 2 YEARS AGO

    What gauge of wire should be used to ground the outlet to the box? Does it matter if you use solid or stranded, sheathed or unsheathed wire?

  • Gregg Stengel 2 YEARS AGO

    Started to replace a grandparents old electrical outlets with a new plate, and noticed it has three, two prong outlets on it...and its a one piece plate. There is only a black and white wire attached to the back plate/outlets. All of the three outlets work, and then I noticed several others in the house that are just like that. Instead of the normal two plug in outlets, it has three two prong old outlets that is a one piece plate. Can these even be replaced with a standard double outlet (three pronged)

    • Reuben Saltzman 2 YEARS AGO

      Gregg - the process for replacing the 'triple' two-prong outlets is the same as for the double. The outlet box that they fit in to is the same size.

  • jim campoli 2 YEARS AGO

    If the metal box is grounded, isn't the green screw connected to the box via the mounting screws? why run another wire to the back of the box especially if metal cased wiring was used (BX)?

    • Reuben Saltzman 2 YEARS AGO

      Hi Jim, That same question came up on my blog post on fixing ungrounded three-prong outlets. Here's what I wrote: The answer depends on the outlet. A self-grounding outlet will do exactly what you’re talking about, but most outlets are not self grounding. The next time you’re at a home improvement store / hardware store, check out the outlets. You’ll notice that the self-grounding outlets cost a little more, and have a little more metal in the frame that ‘bonds’ everything together.

  • Brittany 2 YEARS AGO

    Hello, Great post. I just bought a house and while some of the plugs have been updated to an independent ground, some have not been. Why they didn't just do all of them while they were at it, I am not sure. During the inspection, it was mentioned that it might be possible to convert some of the current two prong receptacles because all wiring going into the panel has metal conduit. I was looking for a way to test this and perform it correctly, and this post provided the information I needed, so thank you very much. (you would not believe how many other sites I found that hinted at it but did not explain anything clearly). I do have one question remaining though: This was originally posted in 2009. Is converting a two prong ground to a three prong ground [by using the grounded receptacle box as shown in the second picture] acceptable for current (2012) code? I know the code can change and just wanted to be sure. Thanks.

    • Reuben Saltzman 2 YEARS AGO

      Hi Brittany, Thanks! Good question - the process remains the same. Everything in this post is still applicable today.

  • Ed 2 YEARS AGO

    I have two prong outlets. I wanted to convert to three prong without grounding (I will go back and address that later. I'm just tireord of constantly looking for adapters) I popped out the two prong receptacle and the old receptacle only had two connectors instead of four like the new ones. When I looked inside the box, the two white wires were spliced and the two black wires were spliced. First question: Does it matter if I use the spliced wires or do I need to split them and use all four connectors on the new "dual pole" receptacles. Second question: When I go back and ground them will it matter?

  • Kacee 2 YEARS AGO

    I have a 2011 truck with a two prong plug but I cant plug my computer into it because my computer has three prongs. Is it possible to get an adapter or is this unsafe?

    • Reuben Saltzman 2 YEARS AGO

      Kacee - good question. I can't think of any situation where this would be unsafe. I wouldn't hesitate to get an adapter and do it myself.

  • Chris 2 YEARS AGO

    I tested my two pronged outlet to see if it was grounded as shown above. The light on the tester lit up but was dim. Is it safe to use an adapter?

    • Reuben Saltzman 2 YEARS AGO

      Chris - no, a dim light on your tester indicates it's not properly grounded.

  • Cole 2 YEARS AGO

    Could I plug a power strip into the adapter?

  • Reuben Saltzman 2 YEARS AGO

    Andrew - sure, as long as the metal screw is grounded and you install the adapter properly. You can check this with a two-lead tester, as shown above.

  • andrew 2 YEARS AGO

    Could I use the adapter for an air conditioner?

  • Bob 5 YEARS AGO

    I live i Iowa and have a house that has two wire wiring throught the house. The house was built in 1960 so I dont know if 3 wire existed or not. In any case, all my elect boxes are metal but I know for a fact there is not metal conduit back to the box. I don't know of any house that has there house wired and in metal conduit . It would cost a fortune. Sorry just my opinion. I dont know but I would think many homes are built with 2 wire back in the 60's. So my question is to ground these elec. boxes they have to be changed to GFCI?

    • Reuben Saltzman 5 YEARS AGO

      Hi Bob, To properly ground these outlets, you would probably need to run new conductors back to the panel, and it sounds like this probably would cost a lot of money. Changing out the outlets to GFCI outlets would give you three prong outlets, which would add a level of safety, but the third prong wouldn't go to anything, so this wouldn't actually give you grounded outlets.

  • Kathy 5 YEARS AGO

    Great post, very helpful and informative. Thank you. This is the clearest information I have found on this topic.

  • Christopher Currins 6 YEARS AGO

    Nice post. Very informative, especially regarding the three-prong adapters. It's amazing how many adapters I've seen in my lifetime not installed correctly. The average person doesn't understand what the metal tab is for. Safety and knowledge when it come to electricity are extremely important.