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Question DetailsAsked on 4/14/2014

What is the average cost for upgrading the electric from two - prong to 3 - prong outlets?

We currently do not have any other information regarding the type of grounding already installed. The house was built in 1960 and looks like no electric upgrades have ever been made. We would just like to see some possible scenarios for upgrading the electric and what the cost would be. It will help us in placing an offer on the house.

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2 Answers


Why do you want the 3rd prong? I'm seeing a lot of non-metallic appliances these days with 2-prong plugs. If you have lots of metal surfaced, 3-pronged appliances, then you should probalby have the 3rd prong.

The 3rd prong is ground

Among electricians and inspectors, ground is among the most mis-understood topics. Expect to hear some wildely varying opinios.

I've discussed this senario with 2 of my local inspectors. As usual this job is a lot easier with a single story house with a crawlway or basement.

The least expensive, least distructive method is to run a heavy gauge ground wire from the panel to the crawlway or basement. In the basement, tap off this heavy ground wire with smaller ground wires to each of the outlets. There is no need for ground rods but installing them may not be such a big deal. Make sure to talk to the inspector before embarking on this course of action to make sure they are onboard with such a plan.

You may be able to do something similar using the attic but fire blocks in the wall can make this time consuming, costly and possibly destrcutive.

I think most estimates will be $3000 - $12000 to rewire the house. This will not include wall patch and paint. Lots of wall will be torn up in the process of runing cable.

Answered 6 years ago by Kestrel Electric


Hate to say it, but Kestrel Electric fell down on us it this time, after such a long run of very good responses.

The code specifically prohibits terminating grounding at the distribution panel (breaker box) - you have to continuously bond to the panel ground bus with the individual circuit ground wires, but the ground bus in the panel then has to be bonded through the outside main panel to two (one in older code versions) ground rods or other approved ground. Just counting on the electric company ground wire is specifically prohibited for good reason - frequently trees fall and take out only one wire, which is commonly the ground/neutral wire, which would leave you with no ground path at all. In fact, many power lines do not even have a ground from the power company - my house is an example - without the ground rods there would be no true ground, onlly the neutral which is actually carrying juice.

Cost for your house depends on the type of wiring you have - if you have 3 wire Romex which would have a black and a white power wire plus a ground wire that might be bare, paper-sheathed, or green insulation sheathed if from the 60's; or maybe AC or BX conduit which has a bonding conductor or metal sheathing respectively, then assuming the ground wires orconduit are connected properly at the breaker box, you might just have to install 3 prong outlets at each location and connect onto the ground that is already there.

Kestrel is right that the industry has successfully leaqd (conned inmy opinion) the Underwriter Labs and code committees into accepting two-wire appliances and tools and such over three-wire, removing the safety of three-wire grounding in favor of cheaper construction of appliances. Then over the past 20 or so years that has been allowed, it turned out a lot of breakers were not tripping during shorts, causing fires and electrocutions. I have personally seen several tool and appliance fires due to dead shorts, including a toaster arcing to the outlet from the metal case, without tripping the two-wire bereaker. So, then the code was changed to require much more expensive ground fault and arc fault interrupters to make the breakers trip during shorting or arcing, which used to be pretty well covered by three-wire wiring.

Generally, 3-wire outlets are smart to my mind, but would actually be considered a step backwards in time according to current code. I actually don't know if that sort of reversion would be contrary to code - a quick search drew a blank on the subject, but I got the impression it is legal if done right.

One other option which is used a lot, and legal in probably most jurisdictions, is to replace the 2-prong outlets with GFCI outlets, which avoids the tearing into walls but costs probably $30-45/outlet to do. That provides fair protection against a short or ground fault in the device that is plugged in, but in some cases does not protect against a fault in the in-wall wiring itself, depending on the type of GFCI. There are ones designed to protect the entire 2-wire circuit as well as trip out due to shorts or ground faults in the appliance itself - they cost about $20 each as opposed to about $10 each, plus installation. However, this will NOT give you a true ground, which many electronic devices, most motorized devices, and most larger wattage kitchen appliances want, so you might end up needing to install a ground to at least some circuits.

You need to have anelectrician look at the layout and give you a firm bid before you count on an estimated cost to include in your offer. My recommendation would be to decide what you want done, then require that as a condition to the offer - and leave all the risk of cost overruns with the seller, then if he accepts have your electrician inspect the result to be sure it was done right and the way you specified.

Answered 6 years ago by LCD

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