Using this wiring diagram let me show you some examples of different scenarios were you would use these wiring methods.
Lets say this circuit was for a long wall in the living room, all the outlets are on one wall and the home run from the breaker box came to the living room and you put it into the box located in the center of the circuit. You would make your connections like box 1. The next boxes you would come to would be wired like boxes 3 and 4. Then on ether end of the circuit you would have boxes like 2 and 5.
The easiest way is to pull a circuit is to pull the home run to the first box in the circuit and then pull a power out to the second box then out to the third box wired like boxes 3 and 4 then the last box being like ether box 2 or box 5. For example lets pretend the power entering the top of box 3 is from the breaker box. Power in from the top, power out through the bottom headed to box 4 then box 5.
Now if you had a living room circuit like I just explained above and you wanted to add an outlet above say box 4 for a TV that you want to mount on the wall, you could fish a wire up the wall into a cut in box at your desired height. You would then make your connections in the existing box (box 4) just like the connections are made in example box 1 and the new box would look like example box 2.
This wiring diagram shows how a single pole switch is wired with two outlets. Multiple outlets can be added by duplicating the wiring shown on the bottom left of the picture above. This is a typical way to wire a bedroom circuit.
This GFCI wiring diagram shows how to GFCI protect multiple outlets. On the back of the GFCI it will say LINE and LOAD, LINE is for your power source coming into the outlet box and the LOAD is for the outlets down from the GFCI. Think of LINE as “power line” and LOAD as the load you are putting on the circuit. GFCI outlets are good for an older home with ungrounded outlets. Place a GFCI in the first outlet in a circuit and run the additional outlets off to the LOAD side of the GFCI. The GFCI will trip when it senses any difference between the hot and neutral and trip. Also see how to wire a GFCI here. How to wire a GFCI
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