I am installing a GFCI outlet in the kitchen (20 AMP) the box that it is already installed in has more than nine wires running into it. What I need to know is how does one determine the load wires from line wires when there are multiple wires running to an outlet box?
Nine wires? sounds kinda sketchy. you may have normally two black (positive or load) and two white or neutral wires plus a green or bare copper cable for ground. it sounds like hobo joe who wired the place decided to add a few lights and whatever else to the positive feed of the original box. If you can find out what wires do what and add a junction box for all those extra wires.
you do not. and repeat do not as this is a botch job, get a qualified electrician, before some person is electrocuted.
Nine wires or nine cables? Nine wires is possible if there was a three-way switch in that box previously, or multiple outlets. Need to know what was in the box before. Pictures would also help.
You use some test equipment to determine which is the line cable. All of the grounds are connected together. Identify each of the remaining wires with numbers BEFORE you disconnect anything. After that you can make a wiring drawing of the connection box and device before you disconnect anything. Once the drawing is done you can tun off the circuit(s) and begin the changes. The line/hot wire and it's neutral are connected to the G F I line connections, the load connections are made to protect any down line devices. If you do not need to protect the down line devices all of the connections can be made before the G F I device. If this seems too much of a challenge for you the best solution is to have a qualified professional electrician do the work.
if you have three romex wires coming to the box (which isn't uncommon) then each has a white, black, and bare copper ground. if you have 4 concuctor wires then there will also be a red wire too, 4 conductor wires are used to run to ceiling lights so you can use one wire but feed 2 switches like separate control for ceiling fan and light or vent fan and light for bathrooms. to determine the line vs load wires you need to take note of how everything is connected and write it down, then disconnect the wires and use a volt meter to see which black wires have power. once you do this follow it back to where you see the outer sheeting covering all three wires (white, black, and bare copper ground) in that romex wire and this is your power supply in. the rest are your load wires. as noted you should have some electrical experience to be doing this because if things aren't connected correctly it can be a fire hazard. in your case if all you are doing is swapping out a regular outlet for a gfi then its easy because all white and copper wires are common connections and connected to each other so just connect your GFI as the other outlet was connected with black as your load side and connect the ground wire to it. if you are trying to put in a gfi to also protect the rest of the outlets on that line then determine the black that has power and that goes to your load side and the rest of the blacks are fed from the load side terminal controlled through the breaker
