TRUE 50a vs BOGUS 50a

We are in a park where I have discovered that the 120v/240v 50a outlets are not wired according to code. I discussed this with the campground manager and she finally admitted that she doesn't really know what it means, but that "they told me we don't have the normal third wire."  What I find with a multi-meter is that both power legs have 120v when read to ground or neutral. BUT when metered across the two power legs, my meter reads 1v. I tested several outlets in the campground and got identical results, so am reasonably sure the entire campground is the same. My assumption is that both power legs are hooked up to the same circuit rather than two circuits of opposite phase. As I understand the requirements of a 120v/240v 50a outlet, a 240v appliance would NOT work on this circuit. However ....

Here's my question
... am I right to assume that when a 50a RV is plugged into this circuit, the RV WILL be receiving TWO legs of 120v/50a power? (still receiving the normal total 100a that a corectly wired 120v/240v 50a circuit would provide?). 
... and am I right in believing that there is at least a possiblity that the neutral on this circuit could in some circumstances be carrying up to 100a???

They are wired properly. RVs don't use 240 volts, they use two 120 volt legs. It is different than house wiring. Different outlet.

Sorry, Tom.  You're wrong on this one.  This is not up to code.  RV 50 amp service uses the same 240/120 socket that's used for a 50 amp electric stove service, and the same rules apply.

Feeding both halves of a 50 amp socket from the same 120 volt source will indeed put the SUM of the current of both legs onto the neutral - up to 100 amps if you try to pull 50 amps from both.  Normal 240/120 volt service puts the DIFFERENCE of the currents on the neutral.

You can pull up to 50 amps from either side - or up to a total of 50 amps from BOTH sides (i.e. 20 amps on one, 30 amps on the other) without exceeding the 50 amp neutral current rating.  As to whether you can actually do that - it depends on the park wiring.  I stayed in one park that provided the proper 240/120 volt service, had 50 amp breakers in the site pedestal, but the site itself was fed by #12 wiring, protected at the off-site meter by 20 amp breakers.  So you couldn't draw more than 20 amps from each leg without tripping the breaker at the meter.

In any case, you should not exceed 50 amps total (i.e. 20 amps from one side, 30 amps from the other or 40 amps from one side, 10 amps from the other) or you'll overload the 50 amp neutral.

The problem is this: There are not 3 but 4 wires on a 50 amp outlet,, Though only three are normally used, the 4th is "Just IN Case" and should never carry current (That is the Green or bare wire, on the plug it is the round or U shaped pin.. Thus we will ignore it.

Now... On the other two

If the plug is wired properly you have three wires

L-1  Neutral and L-2

Electrically L-1 and L-2 are the ends of a transformer winding and carry 240 volts.. THERE is ONE THING in an RV that needs 240 volts, it is also optional.. it is the energy management system. (If it does not see 240 volts, or at least some serious voltage, L-1 to L-2 it assumes 30 amps.. WHICH IS GOOD.  Do not override it.

Now the problem

Let's asume you are running both A/C's heating water and running the microwave.. Roughly 25 amps per leg.. (I'm keeping it safe)

Normally, with such a balanced load,, L-1 carries 25 amps,  L-2 carries 25 amps, and the neutral... carries nothing.

However where you are,  L-1 carries 25 amps, L-2 carries 25 amps, and Neutral... FIFTY

Now,  this is safe.. the neutral wire is rated for 50 amps.

BUT.. If you draw any more current... On either leg .. (Say an electric oven or hot plate to save on propane) You are in danger of overheating the neutral wire and getting a visit from one of the groups that still makes house calls....... The fire department.

An EMS.. Will limit you to 30 amps by default on such a system.. That is also safe, very safe.

Otherwise, if you do not have an EMS.. You will have to be careful about power use.

50 amps is safe.. 60 should be,  But the full 100 you are capable of pushing down that white wire.. Is a bit more than it should take.

That said.. On my rig.. Well, the generator only puts out 50 amps and it can run everything in the Motor Home.. AT THE SAME TIME.

I stand corrected.

My EMS displays amps being used when on a 30a connection, or when running the generator ...it does NOT show me amps being used when connected to 50a shore power. Plugged into this "50a" outlet, the EMS identifies the connection as 50a and does NOT show us how many amps we are using.

When the campground manager told me "we don't have the third wire" I first thought what she was saying was that only one leg was powered, and that they don't have the second power leg. But in testing the outlet, I found that is not the case. Both legs are definitely powered with 120v ...the only aberration is that I cannot reat 240v across the two power legs.

Plugged into this "50a" outlet, the EMS identifies the connection as 50a and does NOT show us how many amps we are using.

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I don't see how that could be, since the EMS uses the presence of 240V to detect 50A service, in which case it lights the 50A indicator and shuts off the amps display.

Paul you are correct.

I agree with Gary.. I'm wondering how the EMS knows it's a 50 amp site, Less you used a manual override.

No override involved ...the EMS in this case is the oem Winnie management system. It does not have over/under voltage protection but does do load shedding ...I presume when on 30a, 20a, or generator systems only as there should be no need for load shedding on a normal 50a outlet. I also have a hardwired TRC SurgeGuard that shows two power legs are powered. I presume when the Winnie EMS sees two power legs incoming (which would be 240 total voltage though the legs in this case apparently are in phase rather than opposite) it shows 50a incoming.

Even on a 30A connection, both legs would be powered with 120VAC and in phase, as they are now.  The EMS can't tell your in phase 50A service from a 30A service, so it should not be showing what it does.

Winnie uses the Intellitec EMS under the Powerline logo and I am intimately familiar with its internal logic. There is no magic here - 50A single phase is electrically indistinguishable from 30A single phase (until the source circuit breaker trips, that is).  There is even special signal circuitry in the EMS to tell it when the generator is running, because it cannot tell generator from shore power either. The only thing that Intellitec is vague about is how much voltage difference there has to be between the legs to conclude it is 50A/240 rather than 30A/120. It has to be more than 1 volt, but may not be a full 200+.

The good news is that when your display shows 50A and no amps reading, the EMS is in bypass mode with no load shedding, so you can enjoy whatever power is available.

  Lets make this simple if both 50 amp legs are of the same phase L1 or L2 you will over load the neutral which is a a # 6 wire rate at 50 amps. The legs must be of opposite phase so they oscillate on the neutral and not hit at the same time ' You are right if you were using 240 volt you do not need a neutral but in a 50 amp RV you are using 2 120 volt legs and need a neutral to complete the circuit

All good advice here so far.

A permanently installed 50A outlet, in the NEMA 14-50R configuration usually used by RVs equipped for 50 amp service, would technically be miswired if the two hot legs are connected to the same phase and would be a violation of any major electrical code.

If properly breakered with a single-pole 120 volt breaker, or wired to just one pole of a 50a double-pole breaker, such an installation doesn't really pose a safety problem since the neutral can't be overloaded without tripping the breaker.  Who knows, maybe the local inspector went along with it, especially if the campground was converting pedestals from 30a only and didn't have the other leg available without planting new cable.  I would guess that's how it's wired and why it was wired that way.

As others have noted, most rigs don't draw more than 50A, total, at 120 volts, though if you have two air conditioners, a water heater, and a microwave you could probably do it.

Lets make this simple if both 50 amp legs are of the same phase L1 or L2 you will over load the neutral which is a a # 6 wire rate at 50 amps.

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You are making two assumptions which are unknowns and not provable here.
#1, you are assuming the neutral is 6 gauge or less. Probably true, but unknown.
#2, you assume that each hot leg has an independent 50A source. Maybe, maybe not, but in my opinion unlikely. If the two legs share a single 50A feed, there is no neutral overload.

I say #2 is unlikely because there would be no reason and no benefit to the campground to run two hots to the site and not use alternate phases. All it does is cause them future problems. Running only one hot and jumpering both terminals of the 14-50R to a single 50A line saves a lot of expensive wire and doubles the number of sites that can be powered. Typically a 200A load center is used to power 5 x 50A sites, but using the single hot allows them to power 10 sites from that same 200A load center. Big cost savings in installation and possible ongoing savings in limiting the available power. And most RVs will never know the difference.

Murph said:

  Lets make this simple if both 50 amp legs are of the same phase L1 or L2 you will over load the neutral which is a a # 6 wire rate at 50 amps. The legs must be of opposite phase so they oscillate on the neutral and not hit at the same time ' You are right if you were using 240 volt you do not need a neutral but in a 50 amp RV you are using 2 120 volt legs and need a neutral to complete the circuit

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Gee.. I too commented on the overload of the neutral.. That is the danger.. If you draw more than around 5500 watts (The output of MY generator) you will overload the neutral wire.. This could result in the Fire Department making a motor house call.