How To Convert Two-Prong Outlets To Three-Prong

By
Home Inspector with Structure Tech Home Inspections

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.  This is only an overview of the steps that a qualified person would take. 

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 1962, which minimizes the risk of electric shock, and allows surge protectors to protect your electrical equipment, such as televisions, computers, stereos, and other devices.

The ideal 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 pretty 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 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 the best possible protection against shocks, but without a ground wire, this outlet will not provide any protection for your electrical equipment.  A surge protector plugged in to an ungrounded outlet will do nothing (you could fry your new plasma TV).  You will need to add a sticker to the GFCI outlet that reads "No Equipment Ground" - this sticker comes with every GFCI outlet.
 

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

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Reuben, great advice, going beyond the scope and really educating the public.

Mar 06, 2009 09:30 AM #1
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Jim Luttrall

Reuben, pretty good explanation. I was really expecting to see problems when I saw the title of your blog since converting outlets is usually done wrong.  One thing I would like to emphasize is to use a tester to make sure the metal box is grounded, you can't skip this step!

Jim Luttrall - Mr. Inspector - Allen, TX

Mar 06, 2009 10:28 PM #2
Rainmaker
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Jim Frimmer
HomeSmart Realty West - San Diego, CA
Realtor & CDPE, Mission Valley specialist

I'm fortunate that all the condos in my farming area have three-prong outlets, but my home inspector does occasionally find some of them miswired.

Mar 10, 2009 09:59 AM #3
Rainmaker
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Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Minneapolis Home Inspections

Jim - The fix for an ungrounded three-prong outlet is the same.

Mar 10, 2009 09:29 PM #4
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One of the best, if not the best, posts I've read on this subject. I feel a re-blog coming on.

I'd also like to congratulate you for getting 11 comments from me today in your blog. That's rare, and requires one of my famous cheers:

  1. Reuben rocks!
  2. Reuben rolls!
  3. Reuben rules!
Mar 23, 2009 03:20 AM #5
Rainmaker
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Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Minneapolis Home Inspections

Russel - thanks for all the reading and all the comments!  The input is much appreciated.

Mar 23, 2009 06:27 AM #6
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Chris

What if the outlet is an older two-prong version that does not have a larger and smaller slot?  Does all of the above still apply?

Sep 15, 2010 04:06 PM #7
Rainmaker
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Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Minneapolis Home Inspections

Chris - yes, all of the above still applies.  Substitute 'hot' or 'ungrounded' conductor for 'smaller slot'.  

Sep 15, 2010 04:49 PM #8
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Bryan

I am installing one of those adapters.  Do I take off plate and connect adapter than screw in faceplate back on over adapter??  I just want to clarity because I have one outlet in my room and its a two prong, I desperately need 3 prong recepticle.

Jul 13, 2011 01:17 PM #9
Rainmaker
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Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Minneapolis Home Inspections

Bryan - no, leave the cover plate on.

Jul 13, 2011 05:10 PM #10
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Monica

I live in an apartment complex and my landlord refuses to change the 2 prong to 3 prong because he says it is not in the contract.  I bought some of the two prong to three prong adapters but I'm afraid to put them in because I can't cut the electricity off.  What can I do?

Jun 19, 2012 09:56 AM #11
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Reuben Saltzman

Minneapolis Home Inspections
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