SAFETY WARNING: NEVER, EVER, consider using a double ended male electrical cord! These are commonly called "suicide" cords for a reason. When you plug one end in, the other end has exposed, energized contacts that can and will electrocute anybody or anything who comes in contact with them. Electricity doesn't care who you are or what you are doing. It's an equal-opportunity killer.Some terminology to keep in mind:
Voltage = the electrical force that makes current flow in a conductor. The unit is Volts (V). Think water pressure in a pipe.
Current = the amount of electrical energy flowing in a conductor. The unit is Ampere Amps or A). Think volume of water flowing through a pipe.
Alternating Current (ac) = With out getting too technical, ac power "flip-flops". If you were to look at the voltage on a graph, it would make a sine-wave at 60Hz (cycles per second). Your house operates on alternating current.
Direct Current (dc) - Electrical current where the voltage remains the same. If you were to look at the voltage on a graph, it would be a straigh, horizontal line. Your car battery is direct current.
Converter = An electrical device that takes 120Vac in and produces 12Vdc out.
Inverter = An electrical device that takes 12Vdc in and produces 120Vac out.
Shore Cable = The power cord that provides power into your trailer from an external source such as the campground power pedistal or household electrical outlet. The term "shore cable" comes from the fact that ships in port will use cable to bring in electrical power from the shore facilities.
Adapter = a device used to adapt one electrical connection to another without changing the type of electrical power utilized.
As previously stated, your trailer has a shore cable somewhere. It will be coiled up inside, but accessible from the exterior through either a round or rectangular hatch. Either hatch will have an inverted "U" door that the cord will pass through with the large hatch closed. See the two following photos:
Your hatch may or may not have the sticker shown. They tend to wear off after a few years.
The end of the shore cable will have a TT-30 plug (for the trailer age/size described). It should look something like this.
This plug operates at 120Vac, same voltage as your household outlets. A difference is that it is rated to carry 30 amps, and as such, it has a different plug. Obviously this won't fit the outlets at home which should be a NEMA 5-15 or 5-20 designation; both are similar and most people don't notice the difference, the 5-20 version has the extra horizontal slot as shown below:
You need an ADAPTER to plug the shore cable into your household outlet. The least expensive option is the stubby adapter that is about 2" long and about the same diameter as the TT-30 plug. It has a household-type male plug rated for 15 amps and a female TT-30 receptacle on the other side. You can see my stubby adapter on the shore cord below. Mine is a 90-degree one, most common is the staight through version with the male plug side opposite of the female side.
The upgraded adapter is basically the same but has a length of cord between the two. This is commonly called a "dog-bone" adapter. The benefit is that the dog-bone adapter separates the two connection points so heat can dissapate better. (I'm actually suprised RoyB didn't include a photo in his post.) I apologize that I don't have a good photo of one of them. With either adapter, you are limited by the household-type plug. This means that you may not be able to run everything in the trailer at the same time such as a microwave, air conditioner, electric water heater, electric space heater, etc.
Inside the trailer, the shore cord goes into a small electrical box with circuit breakers, they are same as the ones in your house. From there, the 120Vac power is fed to the household outlets, the converter, microwave, air conditioner, and other 120Vac powered appliances. The refridgerator often uses two or three sources of energy such as 120Vac, 12Vdc, or propane. The converter may also be located in the same box and you may see automotive type fuses on one side for the 12Vdc outputs.
Power from the converter is at 12Vdc (actually closer to 13.2Vdc-13.4Vdc). This power feeds things such as the water pump, lights, furnace fan. It also connects to your battery so you can use these items when NOT connected to 120Vac power through the shore cable.
Unfortunately, without an inverter and a stout battery bank, you can't use the household electrical outlets without the shore cord plugged into a source. Using an inverter is a whole different set of lessons...
As the OP mentioned, they found the outside receptacle. This is for plugging in lights, radio, or other small 120Vac powered items and not for bringing power into the trailer.
Good luck!
