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Old 04-10-2013, 03:49 PM   #1
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50 Amp Service

If a campground has a 30A, 220VAC service and a non-GFCI 20A 120VAC service, could someone (not me!) use a cheater box and get maybe 45As?

Camco 55025 RV Power Grip Maximizer 45 Amp Adapter : Amazon.com : Automotive
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Old 04-10-2013, 04:07 PM   #2
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The answer to your question is yes. But, I have never seen a 30A 220 volt socket at a campground, and seriously doubt they exist.

The 50 amp service socket, is actually 50 amps at 220 Volts AC, but it is used as two 120 volt circuits by the RV. In other words, the RV is wired internally at the breaker box for two 120 VAC circuits.

(a 240 VAC line is actually two 120 VAC lines, 180 degrees out of phase from one another)
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Old 04-10-2013, 04:19 PM   #3
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That adaptor was made to use with an RV with a 50 amp service cord. The 15(or 20) amp plug side goes to one of the two hot legs of the 50 amp outlet and the 30 amp plug side goes to the other leg of that same 50 amp outlet. Then, in the RV itself some of the equipment is supplied by the 15(20) amp outlet and some by the 30 amp outlet.

The main problem is that the National Electric Code has required GFIC outlets in RV park systems for many years now and thus finding a park without one is rare, and if you do find one, you probably should leave anyway.... it is old and illegal by todays standards.

Second problem is that most AS (don't know about your Land Yacht XC) only had 30 amp power cords to begin with, so for most this is an academic question... but maybe not for your rig.

Third problem is that some of the interior electrical panel will be on the 15(20) amp leg and some on the 30 amp leg. If, lets say one AC unit was on the 15(20) leg, and the microwave was also on that leg, you would pop that park breaker no matter what. In other words there is no way to guarantee how the internal coach wiring has been done and if it will work out for you.

The statement in the ad for it saying you get a 45 amp service is misleading in many ways.

These adaptors are very limited in how useful they could be to you, due to the above reasons.
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Old 04-10-2013, 04:27 PM   #4
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Quote:
Originally Posted by SteveH View Post
(snip)
(a 240 VAC line is actually two 120 VAC lines, 180 degrees out of phase from one another)
Sorry, but I have to get technical here, the 120/240 volt system we use is a single phase center taped and grounded secondary. The two hot lines are called legs, not phases and are not out of phase with each other. They are on either side of the center taped grounded neutral leg of the transformer which supplies the power.

I did miss the statement in the original post about the 30 amp 240 volt outlet, and you are right, they don't exist, especially when you look at the plug on the device in the photo, which is a standard 30 amp 120 volt RV plug.
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Old 04-10-2013, 04:31 PM   #5
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Quote:
Originally Posted by idroba View Post
Sorry, but I have to get technical here, the 120/240 volt system we use is a single phase center taped and grounded secondary. The two hot lines are called legs, not phases and are not out of phase with each other. They are on either side of the center taped grounded neutral leg of the transformer which supplies the power.
I don't want to argue with you, so I advise you to take an AC volt meter, and test a 50 amp 240 VAC circuit (or any other 240 VAC single phase circuit), each leg to ground, and you will see they each measure 120 VAC. The only way you get 240 VAC out of that is if each 120 VAC leg, or whatever you want to call it, is 180 degrees out of phase from each other.
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Old 04-10-2013, 04:44 PM   #6
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You are absolutely correct between each leg and ground is 120 volts, and between the two hot legs there is 240 volts. But the come from a center taped secondary on the single phase transformer and are NOT out of phase with each other, as there is only one phase supplying the transformer. The power company generally has 3 phase power available at the pole, but only one phase of the three is used in residential (and campground) services.

It takes a scope or graphing meter to see that both the 120 and 240 connections are on the same phase, or a look at the transformer connections to see how it has been wired.

I am not trying to be smart ass here, or a know it all, just that the system we use is single phase and the legs are not out of phase with each other. They are two sides (legs) of a center taped secondary single phase system.
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Old 04-10-2013, 04:49 PM   #7
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From Wikipedia:

Leg as in “hot leg” refers to one of multiple hot conductors in an electrical system. The most common residential and small commercial service in the U.S., single split-phase, 240 V, features a neutral and two hot legs, 240 V to each other, and 120 V each to the neutral.

There is no way you can measure 240 volts between the two legs if they are not 180 degrees out of phase from each other. Yes, as opposed to three phase, it is still single phase in the AC power world/lingo, but they are 180 degree out of phase from each other.

If you don't believe it, look at each leg at the same time with a dual trace oscilloscope.
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Old 04-10-2013, 05:06 PM   #8
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We will have to have a battle of oscilloscopes... lol. A single phase system cannot produce multiple phase traces. The legs are halves of one winding on a single phase transformer and thus cannot be out of phase with each other.

It is a one winding transformer which supplies the power, single phase. It is taped in the center, which is the neutral and is also grounded for safety sake. Between the center tap and either of the ends of the winding is half the voltage, in this case 120 volts. Between the ends of the winding the full 240 volts appears. It is still a single phase system, and we call the connections to that transformer "legs".

Thats my story and i'm sticking to it, and my last post on the matter.
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Old 04-10-2013, 05:29 PM   #9
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Look at it with an O'scope. If you were here, I'd draw you a diagram to prove it to you.

"Electricians" use terminology frequently that is not "technically correct". I'm a retired Electronics/Telecommunications Engineer.
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Old 04-10-2013, 06:15 PM   #10
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I agree with idroba.
Single phase is single phase. The power company delivers power thru either a 3 wire or 4 wire system.
Typically the 3 wire systems are used for commercial and industrial systems. A 4 wire system is used for light industry and residential service.
The single phase transformer on the high voltage side (primary) is tapped to one and only one phase of a "Y" connection. The other primary wire of the transformer is connected to a grounded center tap. The secondary of the transformer has 3 wires or taps
. The potential difference across the transformer is 240 volts. The center tap is there to split that voltage to provide for the 120 volts. The center tap on the secondary is grounded in most cases.
There may be a slight and I mean very slight shift between the current and voltage because of the inductance of the transformer. But there is only single phase power available from the secondary side.
It takes two legs (or phases) of primary power and at least two separate transformers to produce multi phase power.
You can produce 3 phase power with only 2 transformers by using connections like a "SCOTT CONNECTION" but the results are you get an unbalanced three phase power where one leg will read a higher voltage than the other two legs.
Rural Electric Power Companies use Scott connected transformers (or similar tapping methods) to save on wire and transformers when providing 3 phase power to their agricultural customers.
You will not normally find multi phase power in a camp ground or RV park.
A three phase "Y" connected 4 wire 240 volt will read 240 volts between each of the phases and 138 volts between any phase and the center tap.
The voltage difference is determined by the potential difference across the windings. Not the phase relationship.
The phase relationship is created by the rotation of the alternator (still referred to today as a generator) that powers the system. It has nothing to do with the transformer. The phase shift created by the alternator is simply carried thru the transformer.
The reason there are different phases is the fact that the alternator at the power company has 3 sets of windings that are 120 degrees apart, in the rotation circle of the device.
Again, it has nothing to do with the transformer.
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Old 04-10-2013, 06:24 PM   #11
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Then you are both probably electricians, and you are both wrong, sorry.

I didn't say it is not "single phase", which is an electricians term. I said, in a 240 VAC circuit, each hot leg is 180 degrees out of phase from the other. If it were not, you would measure 0 volts with a meter between the two.

Both of you go look at it with a dual trace O-scope.
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Old 04-10-2013, 07:03 PM   #12
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I am an electrician and I am also an electrical and electronics engineer.
I am no sure what kind of scope you are using to see the multi phase you claim you are seeing. But there will only be one sine wave on the scope. Crossing the 0 volts line on the scope at 180 degree intervals. Just because the sine wave crosses the zero line and the positive peak is 180 degrees along time line and the negative peak is 180 degrees along the time line. It doesn't mean there are more than one phase. It is still a SINGLE sine wave.
If you were to look at a 3 phase system with a scope, you would see THREE sine waves, each of which would be 120 degrees apart as they cross the 0 volts line on the scope.
You can prove this very easily by connecting your scope to an automotive alternator. It is in fact a 3 phase AC device. Which uses a full wave bridge and voltage regulator to create the DC power to charge a battery.
You will have to connect the scope ahead of the rectifier to see the 3 phase AC.
When I get time I will post pics on the single phase sine wave and a multi phase sine wave as the scope sees it.
And here is your quote. There is no way you can measure 240 volts between the two legs if they are not 180 degrees out of phase from each other.
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Old 04-10-2013, 07:14 PM   #13
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I am NOT talking about 3 phase power!

What I said was "a 240 VAC line is actually two 120 VAC lines, 180 degrees out of phase from one another".

If you take a dual trace O-scope, attach channel A probe to one leg of the 240, and channel B probe to the other leg of the 240, you will see that reference the ground, or neutral, when one leg is positive 120volts, the other leg will be negative 120 volts. That is 180 degrees out of phase with each other, but it is NOT multi, or three phase.

Look at it with a dual trace O-scope the way I said, and you will see it.

And, this whole discussion started about 50 amp service into an Airstream. There is nothing in a 50 amp service Airstream that uses 240 VAC. It is utilized in the trailer as two 120 VAC circuits.
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Old 04-10-2013, 07:28 PM   #14
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I'm no electrician. I'm not an electronic engineer. But I know unless you bring impedance and phase shifting into the discussion you guys will never reach an accord.
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