RV Receptacles, Plugs, Cords, and Adapters 101

[wmtire]

This thread is going to hopefully give those reading a basic understanding of the common outlets/plugs and cords you may encounter with a RV as well as adapters to use same. We are going to discuss mainly the NEMA 14-50, NEMA TT-30, and NEMA 5-20(5-15) receptacles/plugs you will encounter at campgrounds and at home. All three of these are shown in the diagram below. We will also delve into the NEMA L (Twistlock) connections too.

First off, lets talk about what NEMA is, which is the abbreviation for National Electrical Manufacturers Association. The connections we will discuss all have a NEMA designation/nomenclature. Once you get a little familiar with the terms, it will make it very easy to understand, when discussing these or using adapters.

The NEMA designation will end with a R or a P.
R means it's the receptacle (sometimes called the female)
P means it's the plug (sometimes called the male)

If there is a L at the beginning of the designation, then its a "locking" type connection.

You may also see variations in nominal voltage. For our tutorial purposes 120/125 volts mean the same as so does 240/250 volts. Older sources may still refer to these voltages as 110/115 and 220/230.

These diagrams will make it easy to reference as the thread posts progress.

 

[wmtire]

There are two anomalies to the NEMA naming scheme, which we will explain in this post.

The first is the TT-30. This means it is specifically for travel trailers/RV's and 30 amp, 125 volt. Although the TT is abbreviated for "Travel Trailer" it applies to all 30 amp RV's (motorhomes included) that use this connection and not just a travel trailer per se.

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The second is the SS2-50. The SS means Ship to Shore, and was originally/mainly used for marine applications while at dockside. The RV industry also started using this connection for 50 amp RV's, where the shore power cord attaches to the RV. The ground is actually on the side of these plugs/receptacles, as shown in the following diagrams.

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The SS2 is 125/250 volts whereas the SS1 is 125 volts. This short video may help explain this better, along with another designation you may see on these that has to do with CS (California Standards). If it was all simple, we wouldn't need this thread.

 

[wmtire]

The common receptacles you will encounter on a campground pedestal will be as follows (but not every pedestal will have all three, depending on the age and location of the campground).

1. NEMA 14-50R which is 125/250 volts. This will consist of two hot wires (each at 125 volts), 1 neutral wire and 1 safety ground wire. You can power up to 12500 watts of things because each hot leg (there are 2) is capable of 6250 watts. 250 volts X 50 amps = 12500 watts

2. NEMA TT-30R which is 125 volts only. This will consist of one hot wire, one neutral wire, and one safety ground wire. The NEMA TT-30 designation is specific to Travel Trailers/RV's (TT) and 30 amps at 125 volts only. Please keep this in mind that these type RV's only use 125 volts......and not 125/250 volts like a 50 amp RV does. You can power up to 3750 watts of things with this connection. 125 volts X 30 amps = 3750 watts

3. NEMA 5-20R which is 125 volts only. This will consist of one hot wire, one neutral wire, and one safety ground wire just like the NEMA TT-30R. Many of these receptacles by code will also be a GFCI (Ground Fault Circuit Interrupter) receptacle to boot. You can power up to 2500 watts of things with this connection. 125 volts X 20 amps = 2500 watts. (Side note: A NEMA 5-15P can be also be used in a NEMA 5-20R, but a NEMA 5-20P cannot be used in a NEMA 5-15R)

Even though we used the nominal voltage of 125/250 volts for the wattage figures, you may see closer to the 120/240 volts in real life and/or generators output explained in post # 5 below and will need to adjust the wattage down a bit.

As you can see from the pic below, each of these receptacles may be on it's own circuit breaker. The double pole 50 amp circuit breaker (remember this is a 125/250 volt receptacle with 2 hot wires thus the double pole breaker) controls the NEMA 14-50R.

The single pole 30 amp circuit breaker controls the NEMA TT-30R and the single pole 20 amp circuit breaker controls the NEMA 5-20R GFCI.

Just to note, some campgrounds may have a NEMA 5-15R and if so it should be on a 15 amp circuit breaker.

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[wmtire]

For shore power cords (the cordsets used to connect the RV to a campground electric pedestal or generator), you are normally going to encounter one of two types---direct wired and detachable. We will show the NEMA connections for both types in this thread.
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Direct wired will have one end permanently connected to the RV, and you extend the cord out to connect to the electric pedestal/generator. The 30 amp RV's will have a NEMA TT30P on the other cord end.... while a 50 amp RV will have a NEMA 14-50P on it's cord end.

See pics below for these type connectors. I used pics from Conntek for demonstrative purposes but cord colors and handle ends can vary among manufacturers. The NEMA connection will be the same though.

NEMA TT-30P



NEMA 14-50P

For the detachable type shore power cordsets, you will have a connection shown above on one end, but the end that connects to the RV will have a twistlock NEMA connection. When you connect the twistlock end to the RV make sure to actually twist the connector to lock it in place and make a good connection. Many new RV owners forget to make the twist to lock/connect it, and sometimes forget you must untwist it to remove the cord.

A 30 amp RV will have a NEMA L5-30R connector on the detachable shore power cord where it attaches to the RV....while a 50 amp RV will have a NEMA SS2-50R (this is also a twistlock connector) on it's detachable shore power cord. These detachable cordsets will also usually have an additional threaded ring you use after making the NEMA connection to help keep out rainwater from the connections where they attach to the RV. See pics below:

NEMA L5-30R


NEMA SS2-50R

Up next, generator connections.
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[wmtire]

OK, this post is going to explain the common NEMA receptacles you will find on portable generators but we are going to digress just a little to hopefully give you a better understanding on this. The reason for this detour is that generators usually have the watts in their model numbers. If you have a working knowledge of how watts, amps, and voltage work together... it will help you in knowing what NEMA receptacles you can expect to find on generators. Just know this formula:

Watts = amps X voltage

EX:
3600 watts = 30 amps X 120 volts
12000 watts = 50 amps X 240 volts

So just from above you know a 30 amp RV exists on up to 3600 watts, and a 50 amp RV exists on up to 12000 watts when using 120/240 volts as the base figure. The numbers are 3750 watts and 125000 watts when using 125/250 volts as the base voltage.

So you would be looking for around a 3600 watt generator to fully power a 30 amp 120 volt RV......and a 12000 watt generator to fully power a 50 amp 120/240 volt RV.
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Now the common (but not all inclusive) NEMA receptacles you will find on 120 VOLT generators are 5-20R (which can also accept a 5-15 plug), along with twistlock L5-20R and L5-30R receptacles. You will also find generators with a TT-30R receptacle.

On generators that are 120/240 VOLT capable, you may find the receptacles listed above...as well as L14-20R and L14-30R depending on wattage, and can even find the 14-50R if it's high wattage.

You may run across the terminology that a generator is "RV Ready". According to Champion Generators, this means the generator has either a NEMA TT-30R or a NEMA 14-50R receptacle but not all manufacturers use that criteria.

Here are some pics of Westinghouse generators showing the NEMA receptacles. You can see the watts on the panels to give you an idea of what receptacles are used for the wattage of the generators.

WGEN3600

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WGEN5300



WGEN12000

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Hopefully you are gaining an understanding of the NEMA 5/NEMA TT and NEMA 14 series by now and how they apply to RV's. If you catch yourself looking at generators when inside a big box store, that's not my fault.

Next post, adapters

 

[wmtire]

Adapters

There are a multitude of electrical adapters on the market that will allow you to plug your RV into many different outlets at the campground, a generator, or at your home.

These adapters will come in different colors, shapes, types, etc....but all perform the same function. We will cover the adapter basics here and are going to focus primarily on the NEMA 14-50, NEMA TT-30, & NEMA 5-15 adapters to use on campground pedestals or your home....although there are many more adapters for other configurations.

You may see these adapters referred to as straight, round, compact/miniature, puck type (these resemble a hockey puck), and dogbone/ or pigtail (as these resemble a dogs chew bone)

Hopefully by now, you are becoming familiar with the NEMA terms for each plug/receptacle and if it's 120 volts or 240 volts.

The vast majority (there is one exception I do know of) of adapter manufacturers will use the plug/male end of an adapter first in it's name, then the receptacle/female end of an adapter second.

So a 50-30 adapter would have a 50 amp plug and a 30 amp receptacle.
A 15-30 adapter would have a 15 amp plug and a 30 amp receptacle...etc.
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This would be an example of a straight/round/puck 15-30 adapter


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Here is a compact/miniature/triangle 15-30 adapter


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This would be a dogbone 50-30 adapter


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To test your knowledge, what would this adapter pictured below be called?



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Up next, basic adapters most RV'ers should have and how they work

 

[wmtire]

OK, so you may be wondering how you can connect a 30 amp 120 volt RV to a 120/240 volt power source.... or vice versa on how you can connect a 50 amp 120/240 volt RV to a single 120 volt source, and it all get power. We are going to do a very basic crash course in this. This schematic below may help as it shows the hot lines, neutrals, and grounds for both a NEMA 14-50 and NEMA TT-30 amp RV receptacle. A NEMA 5-20 and NEMA 5-15 receptacle will be the same wiring schematic as a NEMA TT-30 amp one is, just less amperage.



Connecting a 30 amp RV to a 50 amp receptacle:

Since a NEMA 14-50 plug has TWO hot lines, then the adapter will actually terminate one of these hot lines inside the adapter, so there is no way for the end with the TT-30 receptacle to get fed 240 volts, but just one 120 volt line. See this dogbone 50-30 adapter schematic below, but it works the same internally if you have a straight, miniature, etc adapter. You may need this type adapter when you have a 30 amp RV and stay at places that only have NEMA 14-50 receptacles. Sometimes even if a pedestal does have the NEMA TT-30 receptacle, it is the one most used and can be very worn out due to all the other campers before you. If so you can use the 50-30 adapter and be able to plug your 30 amp RV into the 50 amp adapter and be able to use it all.



Connecting a 50 amp RV to a 30/20/15 amp receptacle:

Now we go in the opposite direction. What if you have a 50 amp RV and the campground only has a NEMA TT-30 receptacle on the pedestal, as you may encounter in older campgrounds.

Well since there is only ONE hot line in a 30 amp feed, but you need TWO hot lines to properly feed your 50 amp RV...this is where this adapter below comes into play. As you can see from the 30-50 adapter schematic, the adapter will actually use a "jumper" to connect the one hot line feed to both the hot lines used by the RV. This way, everything is powered in the 50 amp RV...but you are strictly limited as you now can only use up to 3600 watts of things, whereas you could have used up to 12,000 watts when connected to a true 50 amp power feed. You have to keep this in mind when connecting your 50 amp RV to a 30 amp receptacle.....and maybe even less than that should you use other adapters to connect to 20 amp or 15 amp receptacles (which you can).



They also make adapters that allow you to plug in your 50 amp or 30 amp RV into either NEMA 5-20 or NEMA 5-15 receptacles you may have at your house. You can use these when you need to use limited things in your RV and/or let the converter recharge the batteries while at home and/or storage. You can see some of these type adapters in the post preceding this one. Just keep in mind when you are connected to these 20 or 15 amp receptacles, you can only usually use up to 2,400 and 1,800 watts of things in the RV. As we explained earlier Watts= Volts X amps

This website link below has much more information, including how to test receptacles, which you should be doing every time BEFORE you connect your RV to one.

https://www.myrv.us/electric/index.htm


Up next, cheater adapters

 

[wmtire]

Cheater adapters

We are going to touch briefly on a certain type adapter for 50 amp RV's called a Y/Splitter adapter (often times also called a cheater adapter).

This adapter will consist of two male plugs and one NEMA 14-50R receptacle. This is supposed to possibly allow you to connect to TWO NEMA TT-30 receptacles for 7200 watts .......or One NEMA TT-30R and One NEMA 5-15R for 5400 watts.

There are some stars that have to align for these cheater adapters to work, which we will touch on briefly, but need to delve into exactly how a 50 amp RV is wired first. See schematic below and notice the two hot lines referred to as L1 and L2.



The cheater adapters will use one male plug to provide power to the L1 side and the other male plug to provide power to the L2 side of a RV's 50 amp electric distribution panel. The adapter will share the neutral and ground wires between the 2 connections. So if you use a 30/30-50 adapter you are providing the L1 and L2 each with 30 amps.



If you use a 30/15-50 adapter you are providing the L1 with 30 amps and the L2 with 15 amps (or L1/L2 could be vice versa depending on how the adapter is wired).



The reason we talked about the stars aligning is for a few reasons.
First the two receptacles that you plug the male plugs into have to be wired separately (L1 and L2).

Second you cannot plug into ANY GFCI receptacle or it will trip. This goes back to where we talked about a shared neutral. A GFCI is looking for balanced current between the hot line and neutral. Because the cheater adapter shares the neutral between the plugs connected to both L1 and L2, the neutral is not going to carry the same balanced current, thus will always trip.

You are rarely going to find a campground pedestal without a 20/15 amp GFCI outlet, so that makes you only able to use half of this cheater adapter, and thus only half of your 50 amp panel will be powered.

Here is an article from Conntek on this:

https://conntek.wordpress.com/2016/11/29/how-to-successfully-use-a-cheater-box-adapter/

Coming up next, generator parallel kits.

 

[wmtire]

Thread moved to FAQ section