Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the “RV Handbook” and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses an RV’s electrical junction box and shore power cord.
When I purchased my (used) Coachmen Prism, I was told to keep the shore power cord plugged into the onboard electrical box except when plugged into shore power. It’s difficult to access and I really can’t understand why it’s necessary unless I’m using my onboard generator. It’s a 2008/2009 Coachmen Prism Class C with Freightliner diesel power. Any info would be appreciated! —Doug
What you have is called a “J” box (junction box), which is wired back to your generator. Your shore power cord comes directly off your distribution center and you have to manually plug it into the “J” box to get electricity from the generator to the distribution center.
This photo shows an older model from an Itasca Suncruiser. You can see the junction box to the left goes up to the distribution center and the shore power cord is wired into it. The junction box to the right has a plug-in and it is wired to the generator.
Upgrade to an Automatic Transfer Switch
This is the economy version that you need to manually plug into the “J” box. The upgrade is an Automatic Transfer Switch (ATS) that does just what the name says: automatically transfers or switches from the generator power to the shore power.
This photo shows the upgrade we made to the Suncruiser with the ATS that we got from Progressive Dynamics. The shore power cord is coming out the bottom and goes over to the next compartment. The ATS senses the power coming from either the shore power or onboard generator and automatically switches inside the box. It is also time-delayed so the generator has time to get to proper operating speed and is providing stable power. This delay can be disabled if you are using an inverter; however, this unit did not have one. With this model, the generator overrides the shore power.
With the Automatic Transfer Switch, there is no need to plug or unplug the power cord – which is nice when it’s raining and the campground power goes out!
Read more from Dave here.
Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.
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