Ungrounded Three Prong Outlets – How To Fix
April 18th, 2009 | 18 comments
One of the most common electrical defects that I find when inspecting old houses in the Twin Cities is ungrounded three prong outlets. This happens when a standard three prong outlet is wired without the ground wire being connected. Today I’ll give a brief explanation of what the third prong is for, and I’ll discuss a few ways to correct a mis-wired 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.
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 repair an ungrounded three-prong outlet is to establish a continuous electrical path back to the main 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. 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 the first photo below). 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 lower photo below).
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 install a GFCI outlet. A GFCI outlet provides the best possible protection against lethal 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, and 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.
Reuben Saltzman, Structure Tech Home Inspections – Email – Twin Cities Home Inspector
Related Post: Converting Two Prong Outlets – this process is almost identical to repairing ungrounded three prong outlets, and so is the blog.
tina
May 8, 2009, 2:02 am
wat i used to think that the third wire is useless, its just a fancy feature, which actually does not do any thing, but after reading this i am amazed how imp it is.
eric
June 22, 2009, 6:02 am
Does anyone know if the gfi built into an a/c unit good enough or do I need to put in a real gfi in the wall?
Reuben Saltzman
June 22, 2009, 8:03 pm
The built-in GFI on an AC unit will protect the AC unit the same way that a GFCI outlet would.
Reuben Collins
October 12, 2009, 1:19 pm
I was under the impression that the tabs & mounting screws on an outlet were connected to the grounding screw on the outlet. So if the metal conduit is providing the ground, if you’ve securely screwed the outlet into the metal box, it’s grounded in a round-about way. Not true?
Reuben Saltzman
October 12, 2009, 4:39 pm
Reuben – it 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.
Reuben Collins
October 15, 2009, 8:43 am
well shiz. I’ve been doin’ it wrong…
Top Ten Home Inspection Defects For Old Houses | Reuben's Home Inspection Blog
November 2, 2009, 7:54 pm
[...] Improperly Wired Outlets Ungrounded three-prong outlets and outlets with reversed polarityare very common defects. These are shock hazards. You can [...]
peter
April 15, 2010, 11:02 am
my outlets are not grounded and running the ground back to the panel isn’t possible right now (financially). and since you mentioned plugging a surge protector into an ungrounded outlet will be useless, i wanted to know if I could use a UPS back up with my ungrounded outlet. I would like to plug the UPS into the ungrounded outlet, then a surge protector into the UPS, and my TV/PC into the surge protector. Will this help against frying my electronics?
Reuben Saltzman
April 15, 2010, 4:37 pm
Hi Peter,
That’s beyond the scope of my knowledge. That sounds like a great idea… from what I know about UPS devices, all the power actually comes directly from the battery, and the battery just gets continually charged. I ‘m not sure if that would protect you from surges. I can tell you that adding the surge protector would certainly be useless – this would just be an expensive power strip.
Tony
November 19, 2010, 9:05 pm
Hi there i just read your post on this and i had question i recently bought a old house. and i did not notes this when i bought it. but someone had grounded one outlet to a grounding rod. should i unhook this or is it safe as is. the ground seams to function as none of my surge protectors say its ungrounded. so though i would ask here thanks have a great day.
Reuben Saltzman
November 20, 2010, 6:03 am
Hi Tony, I’d have to say I really don’t know. I’m sure it would be better to have it grounded back to the main panel, but for a long time it was standard practice to ground subpanels only using a driven ground rod.
Tony
November 22, 2010, 9:05 pm
thanks for getting back to me the house was built in 1942 the wire looks pretty old i wonder if it is best to leave it as is. anyhow thanks for getting back to me have a great day.
Brad
December 11, 2010, 7:27 am
Several of the 3-prong outlets in a home we are looking to buy are not grounded. Also, there is unprotected romex wiring in a bedroom closet on the first floor. The house is otherwise immaculate. Is this a sign of a bigger electrical problem? or an easy fix?
Reuben Saltzman
December 11, 2010, 1:33 pm
Brad – ungrounded three-prong outlets are certainly a sign of amateur workmanship, but not necessarily a sign of bigger or other electrical problems.
Sorry, but without having inspected the house you’re talking about, I can’t tell you how easy it would be to fix this.
Jack
July 29, 2011, 5:55 pm
Thanks for the info. I have several of these in my old house. I presume it’s acceptable to simply change them to two prong outlets, correct? Grounding them is not practical and GFIs all over the house is expensive overkill for lamp circuits. I presume codes don’t require you to provide grounded outlets in all old work.
Reuben Saltzman
July 29, 2011, 7:10 pm
Jack – yes, changing them back to two-prong outlets is ok. It’s not the preferred method… but it’s legal.
Mike Collins
August 6, 2011, 6:51 am
Hi Reuben, I have a house with a jacuzzi tub. the tub is plugged into an ungrounded outlet, however it comes out of a GFI breaker. Is this adequate protection? Thank You
Reuben Saltzman
August 7, 2011, 6:48 am
Mike – ‘adequate protection’ could be interpreted different ways. The GFI circuit breaker should be enough to protect you from a lethal shock… but this wouldn’t provide any type of protection for the equipment.