Awl knotted up
Shore power

Shore Power

The amount of power required by new RV grows with each new model introduced. Air conditioners, microwaves, entertainment systems, satellite Internet connections, all consume power. The larger the rig, the more room for power consuming devices. Smaller tent trailers are usually limited to 15 Amps, travel trailers and van conversions with a single air conditioner have a 30 Amp connection, larger fifth wheelers and motorhomes with two roof top air conditioning units use a 50 Amp connection.

Even though your motorhome may have a 50 Amp connection, the campground may only have 15 amp circuits at the camp sites. The various umbilical cords are not interchangeable, thus a 50 Amp cord will not plug into a 15 Amp socket. Adopters are available to allow safe interconnection among the various types but you are still limited to the power available at the box. You will not be able to run your roof top air on a 15 Amp circuit.

15 Amp Service

15 amp socket

The 15 Amp service socket is the familiar wall socket in your stick built house. It has two slots and a ground pin hole. One slot is longer than the other and is the neutral line. Some times the plugs in the box at the campground are on separate circuits but usually they are the same. 15 Amps at 120VAC is 1800 Watts. You can run a microwave and a blow drier on 15 amps but not both at the same time. Roof Top air conditioners will not start with 15 amps and may be damaged. Sometimes you will find 20 Amp service. The difference in sockets is the larger neutral slot is T shaped to the side

To check for proper voltage, you should measure 120 Volts between H-N. G is the ground pin. Any other contition is cause to not connect to that socket. Be sure to test with all adopters and pigtails you use in place.

30 Amp Service

Three prong connector

30 amp service is required for an RV with a single roof top air conditioner. The additional power allows operation of more appliances such as a microwave and a refrigerator. The 30 amp 120 VAC socket is shown at left.

To check for proper voltage, you should measure 120 Volts between H-N. G is the ground pin. Any other contition is cause to not connect to that socket. Be sure to test with all adopters and pigtails you use in place.

50 Amp Service

four prong connector

An RV with two roof top air conditioners will require 50 Amp service. This additional power also allows such luxuries as a washer/dryer. huge entertainment systems, etc. 50 Amp service is really 240 VAC split between the two sides. 30 and 15 Amp adopters only use one leg of the 240VAC service for 120VAC. The 50 amp 120 VAC socket is shown at left.

To check for proper voltage, you should have 120 Volts between L1-N, L2-N and 240 between L1-L2. G is grounded. Any other condition is cause to not connect to that socket.

Adopting between the various sockets.

Don't be concerned about plugging your 15 Amp RV into a 30 Amp or 50 Amp service or your 30 Amp RV into a 50 Amp service. With the proper adopters you can connect any RV to any service. You should have a distribution panel in the RV with its own circuit breakers. Those circuit breakers insure that you will not use more Amperage than the RV is rated for. On the other hand, trying to run a roof top air conditioner off a 15 Amp service will not work. The extra load should pop the circuit breakers to the junction box. If you have to connect to a service rated below your RV power requirements, monitor what you use and keep the loads below what is available. For example a 15 Amp service will not support roof air. A 30 Amp service will only support a single roof roof air unit. Be aware that discharged batteries will require more power until they are charged.

30 Amp to 50 Amp service adopter

30 to 50 Amp pigtail

This pigtail connects to the 50 Amp service and gives you a 30 Amp socket for your RV. Only one side of the 50 Amp service is used but you should still have the full 30 Amps available. A 30 Amp to 50 pigtail looks the same only with a 30 Amp plug and a 50 Amp socket. In this case as the 30 Amp service is 120 VAC sometimes only half the RV will be powered.

15 Amp to 30 Amp service adopter

15 Amp plug30 Amp socket

This small adopter has a 30 Amp socket behind a 15 Amp plug. A 30 Amp to 15 Amp adopter will have a 15 Amp socket and a 30 Amp plug.

Safety precautions

Small portable GFI

As mentioned, the power available to a camp site may not be the clean 120 VAC or 240 VAC you have at home. Remember that the 120 VAC is a nominal value. Specs exist for the maximum and minimum value but those specs are for what is delivered to the power panel. What is available at the camp site may be different due to how long the wire runs are, the condition of the various connections between the junction box and the camp site, how many units are in the camp ground using power, etc. 120 VAC may be delivered to the pole out front but if it is a hot humid day in a crowded, poorly maintained campground, do not expect 120VAC to your RV. Never trust the campground power completely. A small Ground Fault Indicator plug is handy to carry and use when using something outside. The external plugs on your RV should be protected by a GFI but you cannot be sure the camp ground plugs are protected.

Check proper connections

circuit tester

A tool that should be in every RVers tool box is an AC circuit tester. They are cheap (usually around $5) and available at any home center or hardware store. There are many shapes and the one in the photo is an old one I have had for years but is typical. They all have a 15 Amp plug on one end, three lights to indicate circuit condition, and a legend to show what the lights are telling you. Before you plug your RV onto the junction box, dig out the necessary adopters and plug in your tester. A broken junction box should be fixed before use.

Check proper Voltage

Line volatge meter

Next to incorrect wiring, incorrect voltage is the most common problem. That long wire run and all those roof top air conditioners are a huge load and can drop voltage to below minimums. One one of the RV lists a member mentioned another severe problem caused by an improper repair. The 50 Amp junction box did not work. Now remember 50 Amp is both legs of 220 with the common. The blotched repair connected 220 across what should have been 120 and did extensive damage to the coach. So before you connect be sure to check the voltage.

There are several version on the market but the one shown is the simplest. Just plug it into a handy socket and continuously monitor your AC. Before plugging the RV into the junction box, use the small tester shown below to do a quick verification. The small tester is also used when you are working on 120 VAC wiring to make sure that it is truely off.

AC  probe

Line conditioning

There are various devices on the market that provide clean power to your RV no matter how bad the power is to the junction box and will protect against surges. They tend to be very expensive but well worth it if as happened to a friend, there is a huge power surge in the RV park. An RV hit and knocked over the main power pole as it was pulling into the park. The wires on the pole fell against the wires leading into the park, delivering a huge power spike to the RVs parked there. That huge spike destroyed the power centers in many of the RVs and took out computers, refrigerators, microwaves, etc. My friend had recently purchased a Huges Autoformer and escaped any damage. Lightening strikes can cause similar problems.


Please email me at don.bowen@eart hlink.net for more information or corrections.

Return to RV electrical technical articles page