My home was built in 2015 and all of the electrical wiring is in conduit and there are no ground wires. I am looking to add another electrical outlet in our bedroom for a wall mounted TV. I used the last receptacle in the series and have wired up both outlets already. What do I do with the ground wire that I brought into the box with the existing outlet that I am tapping off of?
It's apparent the contractor is using the conduit system as a ground. You didn't mention what you are using for the extension but I am assuming it's some sort of approved cable. You can attach the ground to the box the existing receptacle is in. You will find a threaded 10/32 hole in the back of the box. You can purchase a ground screw at just about any hardware store.
I must caution you that if you are in a municipality that only allows conduit systems in houses you should install expansion's in like systems.
Hope this helps, good luck.