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jeffcarlson1 12-11-2011 12:45 PM

Replacing 2 prong outlet + wires might have been switched
I recently changed a two prong outlet to a three prong. I am going to get GFI today and switch it out after reading online that it was not well advised just to replace the two prong outlet with 3 prong. I think when I hooked up the outlet I may have switched the hot wire and the neutral wire. Is this something that needs to be fixed immediately. Also how can I tell which wire is the hot wire. I assume it's the black one but the wires are old Knob and Tube so I am second guessing myself. Is it possible a black wire could be the neutral. Power should run regardless how its hooked up , even if I did switch the wires and incorrectly connect, right?

Also why can't you replace 2 prong outlets with 3 Prong. What's the reasoning?

evstarr 12-11-2011 10:14 PM

That third prong is an equipment or safety ground. It's purpose is to provide electricity an alternate path to ground besides thru you in the event that you are handling some appliance that suffers a fault.
You should invest in an inexpensive non contact voltage tester and identify the hot wire with it and install it on the correct terminals of your outlet.

By code, you can replace a 2 prong ungrounded receptacle with a gfci only if you clearly label it and any others connected to it's load side as "no equipment ground present"

The larger issue is that knob and tube wiring. It was never designed to carry the loads that a house full of appliances put on a circuit and, particularly if it's been interfered with or added onto, it is a significant fire hazard.

jeffcarlson1 12-11-2011 11:38 PM

Thanks for the info. Will a GFCI really provide some safety even If there is no ground available. I read online that it will but was wondering how if it's not grounded. Also I was at the store looking at GFCI outlets and saw no such sticker to identify the outlet with as "no equipment ground " Shouldn't it come with it.

evstarr 12-12-2011 12:55 AM

The gfci will help protect the user at the outlet by tripping if there is a ground fault. Normally the path of least resistance would be the ground conductor back to a water pipe or ground electrode and dissipates to earth. In the absence of a ground wire, the current would go thru you to earth. Gfci operate by detecting if there is any difference in the current flowing between hot and neutral that might indicate that someone is about to zapped. They will not prevent all chance of injury or damage to property but it's a darn sight better than nothing. Note that you can feed and protect additional outlets downstream of the gfci by connecting to the load terminals on the gfci.

remember that you need to label them by code because it is not obvious to the observer that there would be anything nonstandard about those outlets just by looking at them

Purely my opinion but I don't imagine that the manufacturer wants to be liable for suggesting that their product should be a substitute for a properly and safely installed circuit. I guess they figure if they supply such labels then they are tacitly agreeing that its a good long term solution.

That knob and tube needs to come out. If you overload it, the joints or even the conductors could heat enough to start a fire. Don't bury it in insulation.

Good luck!

SBay_ecologist 12-12-2011 01:32 PM

How about connecting the ground on the outlet to the junction box --I have metal ones-- with a pig tail?

I am doing the same thing: Replacing all my two-prong outlets with three-prong ones.

Where it is possible, I will get a copper wire connect the ground-prong hole to my grounding rod. Where it is difficult, I am planning the ground-prong hole to connect to the junction box.


kok328 12-12-2011 03:53 PM

And what makes you think the junction box is grounded ?

nealtw 12-12-2011 04:48 PM

Put one gfi outlet on each cercuit that can not be grounded.

jeffcarlson1 12-12-2011 07:35 PM

KnT has to stay in. I am renting the place so they will not re-wire. I was just looking for a fix for two outlets that can't hold plugs in very well. Thanks for all the info.

Just out of curiosity what will happen if you hook up an outlet with wires reversed. Will you still get power? Should a 3 prong plug tester detect the reversed wiring.

JoeD 12-12-2011 07:44 PM

You should not be doing anything in a rented building. It is the landlords responsibly to repair it. You are opening yourself up to a ton of possible liability issues if something goes wrong in the future.

kok328 12-12-2011 09:03 PM

You will still get power with the outlet wires reversed.
This will show up as an incorrect wiring on a 3-prong plug tester.
Most appliances are double insulated and that is why they only have a 2-prong plug and not a 3-prong plug.
You'll notice that most plugs and outlets are polarized. The neutral plug (left side) is the larger than the hot side to ensure that you don't get the wires reversed. However, you have managed to defeat that precaution by not determing which is hot and which is neutral. Use your tester and make corrections as necessary.

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