I am attempting to install a new GFCI outlet in the living room of the 1940's house I just bought. I made the mistake of not noting which wires were going where on the old 2 prong outlet which was working. There are 4 wires. The outlet box is ungrounded. The wires are cloth wrapped and very grungy looking, but there is no visible difference in color. They are in the outlet in 2 sets. 2 on the top and 2 on the bottom. Ive used a tester to determine that the top set is the line wires, but I just wanted to double check a few assumptions.

1. The 2 pairs of wires will definitely be a hot and neutral in each pair, right? Rather than what should be two black (hot) wires in a pair and two white (neutral) wires in a pair.

2. Assuming the bottom pair is the load hot and load neutral wire, how do i tell which is which? I pulled off another socket in the same room and saw that, on the bottom pair, the bottom wire was going to the brass screw and the top wire was going to the silver screw. Can I assume since the outlets were very close to each other that this should be the same on the outlet I'm replacing?

3. I plan to pigtail the hot wires together and pigtail the neutral wires together like in this guide: Black & Decker Projects and Advice | How to Install a GFCI for Single-Location Protection . If I were to get the load wires mixed up and pigtail the hot line wire and the neutral load wire together instead, would the outlet just not work or is there a danger of an immediate fire?

Thanks!

 

A non contact tester from what I have read will indicate the hot wire, no reaction at the neutral. I have always used either an extension cord with ground plugged into a known good grounded receptacle or a long piece of wire to a metal water pipe and a multimeter. Measure from your test ground to each wire. The wire that reads ~120v to your test ground is the hot, (black). Mark each with colored electrical marking tape after identifying.

 

Thanks for your reply. I have already found out which one is the hot LINE wire though. I just dont know which is the LOAD wire should be installed on the brass screw and which one should be on the silver screw. Since these wires don't have power when they aren't hooked up, I don't know how to tell one from the other since they aren't color coded.

 

Load is not a wire. It is a cable consisting of a black and white wire and no voltage when measured with a multimeter or test light.

 

Again, none of the wires in these outlets are colored. They are all black. I know which wire is the hot wire which I connect to the "line" brass screw and then I connected the wire paired with that one to the silver "line" screw. So I am trying to find out if there is a way to tell which of the wires I am connecting to the "load" screws on the socket is "supposed to be" the black one and the white one or does it not matter? And if it does matter, since I can't tell which one is supposed to go where, is there a danger in just guessing and seeing if it works or will it the outlet just not work if the wires attached to the "load" screws are mismatched?

 

Look at the receptacle it feeds. The wide slot should be neutral. With breaker off and using a long test wire from GFCI to the next receptacle with a multimeter set to ohms determine which wire at the GFCI goes to the wide slot of the receptacle it is powering.

 

Can you post a picture of the wires in the box you have open? See How To Include Pictures In Your Post.

Yes it matters.

It seems to me that that would be safe to try if you know, or can determine, which is the next receptacle down stream.

 

Suggest that when testing for hot or not using a noncontact tester that you test both wires and see that one is hot and one is not.

In other words, if the tester indicates one wire is hot, do not just assume the other is not, and vice versa.

Note that in really old homes (pre-1950) neutral may be found going through switches which is not proper by modern standards.

 

Simply reversing the connections, putting the hot wire on the wide slot and the neutral wire on the narrow slot will work normally on a GFCI receptacle or a regular receptacle. But it is infintely better to get it right the first time.

Backfeeding, putting the feed wires on the load side of the GFCI and the continuing wires on the line side of the GFCI will probably result in unexplained tripping of the GFCI.

Be very careful. If you create a dead short you can fry devices including GFCI units.