Originally Posted by bansil
keep this in mind
50 amp service is actually 2 110V lines coming in, one will have 25 amps available to use and the other will have 25 amps available (these numbers are for demonstration) . . .
Wrong! The "50-amp" 4-pin 120/240 volt RV outlet has a full 50 amps available on each hot leg.
If you are using only 120-volt appliances, and you wire the bus to carefully divide the loads half on one hot leg to neutral, and half on the other leg to neutral, you have a total of 100 amps available at 120 volts. Either way, there are 12,000 watts available, either 50A x 240V or 100A x 120V, or some lesser combination of the two.
If the campground is mis-wired, and both hot pins are on the same supply leg, then you have zero volts at the 240-volt appliances, 50 amps on each hot leg, and 100 amps on the overloaded neutral wire rated for only 50 amps.
If both the outlet and bus are correctly wired for 120/240, then the neutral only carries the difference in current between the draws of the two hot legs. If you have a 1200 watt, 120-volt heater runing on one hot leg (10 amps), and a 60-watt light bulb running on the other (1/2 amp), then 1/2 amp from the heater continues through the light bulb to the opposite leg, and the 9-1/2 amps difference current from the heater returns through the neutral.
The 30 amp, 120-volt only RV outlet is only capable of 3600 watts. It has one hot, the neutral, and the safety ground.
The 3-prong outlet in ZB's photos may be an older 120/240-volt cookstove plug with no safety ground. In Grandpa's day, installers ran a separate safety ground wire from the case of an appliance to a nearby metal water pipe. It instead may be a 240-volt only cord with two hots and a safety ground, and no neutral. If so, there would be no 120-volts available for New World appliances.
Back in the old country, there is no neutral, and no 120-volt half voltage available. There are only two hots. That's why all plugs have fuses in them on both wires, and insulation on the back of the pins so you can't have the plug in far enough to connect to the mains and still have metal to touch on the pins of a half plugged in cord.