I put this info together for a friend. And even though this is well understood by most, I thought it may also be a helpful Forum posting.
50-amp service has 4 wires with two 120-volt HOT feeds.
From this common service we can draw 120 or 240 volts. Each leg is 50 amps @ 120 volts.
Almost ALL 50-amp wired RV's use both sides of the service separately as 120-volts on each leg. Only a few mostly high-end coaches utilize the 240-volt from this same service.
The 50-amp 3-pole 4-wire service is superior to the 30-amp service because of the total amperage available.
30-amp 120-volt service = 3,600 watts
50-amp 120/240-volt service = 12,000 watts
The half round or U is the ground, the one directly below it is the white or neutral and the other two black wires are 180 degrees out of phase with each other are the HOT 120-volt. In reality you have TWO 120 volt split service going into your RV.
X & Y are interchangeable , red and black wires are hot (live) wires , one wire on the X, and the other on the Y. The neutral (white) and the bare ground wire MUST be on their designated connection.
TO TEST 50 AMP OUTLET USING MULTI-METER PROBES with outlet photo below:
meter red & black probes are interchangeable for AC
touch probes to outlet, correct voltage is noted:
W-Y 120
W-X 120
Y-X 240
G-Y 120
G-X 120
W-G 0
IF Y-X = 0, outlet is usable, but total amps should not exceed 50 amps.
If W-G is NOT 0, outlet should not be used.
neutral & hot are reversed and coach frame & outside skin could be electrically hot and shock you.
120 is ok as 110
240 is ok as 220
Some common gear to be used in conjunction with a multi-meter are outlet tester and plug-in volt meters.
Many Forum members including ourselves have made creative custom test cords with a 50-amp male plug and two 15-amp female outlets. Then plugged in gear like these for a quick outlet test before plugging RV into campground pedestal outlet.
A sheet from our Progressive EMS:
Looks good Barry.
To muddy up the water I was at a camp ground somewhere the last month (been so many places lost track which one I it was) but instead of having a 120/240V 1 phase Delta service they had a 120/208V 3 Phase Y service so at the site when you checked to ground each of the two legs had 120V but when checking between the hots only had 208. I was concerned about that for a moment until I realized everything on the coach was set up for 120V and that was what I had.
Correct, good point Turbojack........... if you checked your neutral current it would have been a little confusing to most....
example;
20 amps leg 1
20 amps leg 2
would be 20 amps on the neutral instead of zero
I hard wired a progressive EMS in after my auto transfer switch. It protects everything from generator and shore power failures. I just plug in and never worry about anything!