120 Volt RV Electrical Wiring
It is the season for RVers to be repairing and improving their RV and those repairs have raised some interesting questions in phone calls that I have received during this Covid-19 Pandemic. Answering these questions and others in recent times gave rise to my decision to prepare this TechTip to address some of the changes that have slowly made their way into the production of modern RVs.
Many of us assume that the AC electrical wiring in a RV is the same as that in our stick-built houses. A better description would be to say that the RV 120 Volt AC wiring is similar, yet different. There are few or no conventional junction boxes in newer RVs. Electric receptacles are flush mounted without an electric box.
Often these receptacles are ‘daisy chained’ in a series, all on one circuit. Imagine taking a sufficiently long length of wire and running it to all the locations where receptacles will be located in one area of the RV and that are all on one circuit. Then as the first receptacle is fitted into the finished wall with the wiring feeding out through the wall hole, through the receptacle and back into the same mounting wall hole where it carries on to the next receptacle. The wiring connection (highlighted by the Red Arrow in photo above left) is made by opening the (white) back of the receptacle, laying in the cable, then closing the back and using a tool to press the back onto one side of the cable until the back locks onto the (black) receptacle which automatically makes the connections to the Black, White and Ground individual wires. The wire then carries on to the next place where another receptacle is needed. This is known as ‘daisy chaining’ the receptacles, since one cable connects many and the wire is never cut from beginning to end. This is the primary reason why the circuit breakers in the main panel or modern RVs are labelled ‘General Purpose 1’ or 2 and so on. The receptacles follow the wire not the room or area where they are located,(bedroom, living room etc.) as they are in a stick-built home.
The first receptacle is mounted to the wall panel by tightening two screws at opposite ends and sides of the face of it. (see yellow arrows in top right photo above) When the screws are tightened they swing (white) plastic wings that flip out at 90 degrees to the receptacle’s front surface and engage the wall immediately behind the receptacle. (See yellow arrow in left photo above). Once secure and lined up parallel with the appropriate surfaces, the screws are tightened and a covering plate is pressed into place onto the receptacle. (see green arrows in lower right photo above) There is no wall box, no bare wires attached to the gold, silver and green screws, no wire cuts, mounting screws or clamps to secure that cable at each receptacle. The only exception to this is in the installation of Ground Fault Circuit Interrupter (GFCI). When this type of receptacle is installed in a RV, the individual wires are looped around the appropriate connecting screws. After wire installation the receptacle is wrapped in electricians tape covering all wire connections to prevent contact with anything else. Still not in a box, but more protected than it would be if left without the tape covering
Slide Outs Require Special Wiring Approaches:
When wires need to be connected, then the RV industry has stepped up by using suppliers that produce special connectors that take the place of ‘junction boxes’ and twisted together connections. This is even more important when different types of wires are to be joined. Obviously, solid wires cannot be used in the wiring harness of moveable slideouts which extend and retract numerous times. Properly protected stranded wire cables must be used between the fixed RV body and the moving slideout to maintain integrity of the wiring. Wire connections can be made that ensure a safe, secure and properly polarized wire connection. The photo to the right shows a typical Self-Contained Power Connection (SCPC) as used in a RV. The White, Ground and Black individual wires (above the red arrows) can be seen through the clear cover. This half of the connector is plugged into the white mating connector allowing power to flow in the wiring when the circuit is live. This connector can be placed anywhere in the area and in this photo the connector is attached by screws (green arrows) to the board where the wiring is laying. Here is a link to the types of Self-Contained Power Connectors (SCPC) often used in RV applications:
As you can see from this catalogue, many low voltage (i.e. 12 Volt) connections are addressed in this product catalogue as well. These connectors take little space, can be placed almost anywhere and can be secured with a screw to provide security to the connection.
On the assembly line, the installation process is demonstrated on this YouTube video:
For RVers making their own repairs or upgrades of connections using standard hand tools watch this YouTube video:
I have had the opportunity to use these SCPC units in an RV setting and found them easy to install once you have the room to use a large pair of pliers to secure the two halves together. They are well thought out with polarity and ground markings clearly visible to make it easy to properly insert the wires, stops that make it easy to insert, then clip the wire ends off and a hinged locking cover which takes some strength to properly clamp the halves together, that ensures a tight safe insulated connection. A bonus is that the connector can be secured to a surface to ensure it stays where desired.
Another Innovative Wiring Solution:
I have learned from numerous owners of older RVs that frequently when multiple wires are joined in a standard junction box, that the wire connections become loose, then overheat with evidence of insulation being charred from this heat. The twist-on connectors are usually taped to the wiring after installing them to secure the cap. They are not easy to see since these connections are under the box cover plate. When something does not work, the troubleshooting process leads to these boxes and the loosened connections. While the connector mentioned above would eliminate this issue in production with planning to use them, what can you use in coaches that do not benefit from the newer technology to secure the wiring?
WAGO has developed a number of easy to install connectors known as Series 221 Lever-Nuts® that simply require an individual copper wire to have the insulation stripped back by a specified amount, then insert it into a slot on the connector and flipping a small lever to lock the wire in place. The selection of the Lever-Nut® is dependent upon the number of wires to be joined since they have versions from two to five wires. Here is a link to some information on these:
What is nice with these connectors is that they accept (and can safely join) various copper wire sizes and types (solid or stranded) while making the connection easily accessible for circuit testing without having to disturb the connection.
I have used them, both in 120Volt AC and 12V DC applications and have been very satisfied with them. Not only are they easier to install and more secure than traditional wire nuts, they take up far less space than the conventional solutions. This is especially important in settings where multiple wires must be connected in a tight space where switches or AC receptacles are ganged together then another wire needs to be added.