As a Minnesota Home Inspector I often come across a three-prong receptacle with no ground connection. My clients often wonder exactly what this means, why its a problem, and how to fix it and if they need to fix it. Of course as always anything in my home inspection reports whether I consider it a safety issue or not is ultimately up to the client to decide how to proceed.
In homes you’ll sometimes find receptacles with both two-prongs and three-prongs or slots. Two-prong receptacles are referred to as an ungrounded receptacles, whereas three-prong receptacles are referred to as grounded.
So what’s the difference? All home receptacles have a hot conductor (wire) and a neutral conductor. The hot conductor delivers electricity from your local power source to your home and the neutral conductor returns this electricity back to your local power source. If you have a two slot receptacle, these are the two conductors connected to it.
With three-prong receptacles, there is a third conductor, a ground conductor, and it is a grounded receptacle. The primary purpose of this third wire is to deliver any surge in electricity safely back to the earth. An excess in electrical charges can be a common occurrence in any home and may be caused by any number of things, including lightning strikes, or even large appliance start-ups.
Lacking this third conductor, any excess electrical charges may find an alternative path to ground, which can increase the risk of fire, shock, or electrocution. Put simply, this third conductor absorbs any excess energy, redirecting it to your main service panel, and out too the earth, by doing this it reduces risk of injury and property damage.
In the past, these two-prong receptacles were all that was needed to power low energy consuming appliances, such lamps, coffee makers, etc. as these rarely produced any power surges.
If you only plan on using these smaller lower-powered appliances, in all likely hood, you’re okay leaving any two-prong receptacles in place. However, with modern computers, televisions, stereo equipment, etc. it may be worth considering upgrading to a three-prong grounded receptacle including the third grounding conductor.
Replacing a two-prong receptacle with a three-prong receptacle and not having it properly bonded to the electrical grounding system is simply a cosmetic change and does not increase safety in anyway. You’re in all likely hood increasing risk by doing this, as your more likely to plug in more power consuming appliances.
You may be reading this because I have brought to your attention that you have three-prong receptacles that are ungrounded and are wondering what your options are moving forward? The easy simple fix is simply replace the three-prong receptacle back to the two-prong receptacle that was likely first in place. This may not allow you to use some of the more modern appliances, but it reduces the risk that you will be using equipment on the receptacle that may be prone to short bursts of electrical surges.
The other possible fix is to add a Ground-Fault Circuit Interrupter (GFCI) receptacle. You’ll typically see these in areas that are susceptible to higher levels of moisture, such as kitchens, bathrooms, basements, and outside or in the garage. This will still be an ungrounded receptacle. This option will protect people, but it may not protect sensitive electronics.
The last option of course is adding a ground conductor that is properly bonded to the electrical panel. This of course in most cases requires the most about of work (and expense). It requires attaching a wire and running it all the way back to the main service panel.
The cost can vary significantly in making these upgrades, depending on the scope of work involved. However, you can usually group some of these tasks together to save a bit. Generally speaking, grounding a receptacle costs between $100 to $200. This can go up if walls need to be opened up and repaired. If you’re wondering what it costs to re-wire a home, this can also vary greatly depending on the work required, which may be as simple as re-wiring from attic and unfinished basement access to as complicated as upgrading service capacity and opening up walls, ceilings and floors.
Average Costs by Home Size
1,000-square-foot home: $2,700 ($1,600 to $3,800)
1,200-square-foot home: $3,200 ($1,900 to $4,500)
1,500-square-foot home: $3,900 ($2,300 to $5,600)
2,000-square-foot home: $5,400 ($3,200 to $7,600)
2,500-square-foot home: $6,600 ($3,900 to $9,400)
3,000-square-foot home: $8,100 ($4,800 to $11,400)
As always this is a job for a qualified Electrical Contractor and should not be performed by a home owner.