Trying to run a breaker load box rated 70 amps just 2 spots for breakers

Question

Ok I have a 60 amp breaker at my main box outside of house with 4 gauge wire 2 hots and a common. Im trying to add a 70 amp load center that has 2 spots for breakers that I want to run a 30 amp breaker and a 15 amp breaker out of. the 30 amp will be run to a RV plug. The 20 amp breaker will be run to a reg outside plug.will this be able to work are do I have to use all the power that is being feed in to box. Cause I hooked it up and the reg outlet worked until. I plugged the RV up then when I flipped the breakers on and off in the RV. It turned the reg outlet off. And never had any power in the RV. What was strange is the 60 amp breaker at main did not flip are the 2 breakers I installed did not flip. What did I do wrong

Answer 1

It's called "neutral" not "common" and it's not common at all, it's the normal return current path. You also need a separate ground wire.

On top of the ground wire you also need a ground rod.

Having run 3-wire cable is a bit of a problem. You will be forced to use 2 of the wires for neutral and ground, leaving 1 for hot, and that means only 120V and not 240V. But that is fine, your loads are 120V. And 4 gauge wire is plenty for the 50 amps.

Since the wire is quite large (4 gauge) you can tape the wires green for ground and white for neutral, if they aren't already.

You need to take the 1 remaining hot wire and split it so it feeds both lugs on the panel. That is a hard thing to do, unfortunately. This would've been easier if you hadn't been so cheap on the panel. I would take the panel back and get an 8-space panel. Then you can attach your hot wire to 1 bus bar, and place the breakers on the same bus bar. This will be cheaper than any option I can think of for splitting a #4 wire.

Pro tip, there are plenty of places to save money (like aluminum wire is 1/3 the cost of copper) but scrimping on the panel spaces is not a good choice.