An RV of decent size expects a 4 slot, 50 amp power cable which provides two 50 amp circuits. When driveway camping, most hosts don’t have a 50 amp power connection, so if two circuits are desired (for running two air conditioners, for example) a splitter like this can be used along with a 30 amp to 20 amp adapter to present two 20 amp plugs that can be plugged into two different circuits in the house:
The problem is that most household outdoor plugs have a GFCI in the circuit that looks like this:
The GFCI protects homeowners from shock by insuring that the same amount of current flows back into the neutral return wire as flowed out from the hot wire. If not, it means some of that current is flowing elsewhere, like through a person. When this current imbalance is detected, the GFCI “trips”, and needs to be reset.
Since the RV power system has in its four connector jack two hot lines but only one neutral, using the splitter above won’t work if either 20 amp plug is connected to a GFCI-protected circuit, since the current returning from the two hot lines spills into a common neutral, and is then split by the splitter. Since the current has been “mixed” on the common neutral, the returning current on the then-split neutral will never exactly match the inbound current from the corresponding hot line, so the GFCI will trip. It’s like two parallel rivers: the inflow and outflow on a given river is identical, but if a trench is cut to connect the two rivers, the inflow and outflow on each river won’t match since one river donated a bit of its inflow to the other river’s outflow through the trench.
The solution is to split the neutral, so that each of the RV’s two circuits is completely separated from the other. Here’s the common, single neutral bar in the RV’s breaker box:
I removed the neutral bar and installed two separate neutral bars:
Since the neutral from the RV’s four pin connector now only serves the right side of the breaker box, I brought an extension cord in, cut off the female end, and wired it in on the left side of the breaker box to supply power for the left side. I did the same thing on the right side too, so the right side can receive power from the big 50 amp connector on the back of the RV or through its new 20 amp extension cord. The right side can also receive power from the inverter I wired in a while back, so the three breakers that can provide power have been colored to insure I only turn one on at a time. I also added a second meter so I can repay our hosts for the power used on both circuits:
The new pair of 20 amp power cords come out through the bottom of a compartment. In the plastic tub they’re plugged into a pair of extension cords that lead to the house:
Until now, the common neutral problem has limited us to one 20 amp circuit when driveway camping, which can be uncomfortable in hot weather since an RV this large needs both air conditioners to keep it cool. I’m happy to have finally broken free of this limitation!