I want to replace a 2 prong outlet with a gfci on the most upstream receptacle. I have to find the line and the load. To find the line and the load do I put normal wire nuts on all of the wires, and turn the power on and see which hot one has electricity flowing?
Do I use wire nuts or lever nuts?
Does the line and the load matter if I want to protect everything downstream??
Best Answer
Easier than you think. I recommend a two-step process for attaching a GFCI.
Part 1: LINE terminals.
There is tape on the LOAD terminals; leave it. LOAD terminals are not extra screws for extra wires; they are special and leave them for now.
Note that power enters the box in several cables. Find the cable you think is supply from the panel. Hook its black and white to the LINE brass and silver screws. If all the grounds are clumped together, also hook up GFCi ground to the clump. That's it.
now power up the circuit and test the GFCI receptacle in all respects. It test fires, it resets, if you plug loads into it, they work.
If the GFCI refuses to work properly, you guessed the wrong cable. Do it again with a different cable.
You will finish this part with the GFCI working in all respects.
Part 2: LOAD terminals
You will not disturb the LINE connection further. If you have some reason to need to, then it invalidates your work in part 1 and you must revalidate it by repeating part 1. It wont take long.
Now what happens varies on a number of factors, and is where the skill comes in. Peel off the warning tape off LOAD.
If there is only one more cable entering this box, you can "go for it": just try hot and neutral to the LOAD brass and silver. Power up and test the GFCI and make sure everything still works. Plug a load into every downline socket, and try every downline light switch and hardwired device. If you don't get any GFCI trips, phew your installation passed without complications! You are done.
If anything else, wire them as if the LOAD terminals are the supply cqble. If you get stuck, learn everything you can about the wiring, post some pics, and ask.
Other questions
Wire nuts are fine. Lever nuts are fine. Push-in / stab connections are bad news.
As discussed in part 1, line and load matter, and sorting that out is what part 1 does.
If you cross up line and load, the sockets will work, onward loads will not work, and the GFCI wil not test or reset. That is why I complete part 1 before starting part 2. Trying to do both at once invites confusing problems.