I bought a trailer on a lot to fix and rent out I own a small handyman bizz so I know a little about alot but this is my question... Their is a breaker box on a 4*4 outside under the meter 3 wires going in but inside there are 4 wires ground and neutral going to one bar and then the two hots but I'm not here to ask about the hots. So in the box outside the ground and neutral is on the same bar but inside the trailer in the breaker box the netural is going to one bar and the ground to another they are not touching each other why is the one in the house different then the one outside and 2. Can I repull just three wires instead of 4. It's really old and oxidizing aluminum I want to run new copper but I would like to just run three wire instead of 4 plz help..

 

The box outside is your main disconnect/breaker panel. This is the only place neutral and ground should be bonded. Anything beyond that is sub-panels and neutral and ground must be separated.

No. You must have 4 conductors. One way to avoid that is if you use metallic conduit. Then, this conduit can be used as a ground conductor.

Check sub panel diagram below.

https://www.doityourself.com/forum/e...-diagrams.html