Sunday, May 28, 2023


No power is coming from my RV’s onboard generator. Why?

Dear Dave, 
The Onan generator starts and runs perfectly, but when I start it, it’s not powering up the RV. —William, 2017 Fleetwood Flair LXE

Dear William,
I believe the onboard generator you have is a standard Onan gas generator. Since you did not provide the length, let’s assume it is at least a 5000-watt version. The first thing I would look at is the circuit breakers on the generator. You should have a 30-amp and 20-amp circuit breaker, either on the front or on the side. Some like this one have two 30-amp breakers.

What each breaker does

One breaker is inline of the 30-amp power going to the distribution center, while the other goes to the back air conditioner. This allows you to run both roof airs at the same time by running the generator, with the front being powered by the 30 amps going to the distribution center and the back supplied by either the 30-amp or 20-amp circuit breaker. If the 30-amp breaker is tripped or in the off position, then you will have no power going to the distribution center. Even if you do not have two air conditioners, there will be two circuit breakers and the second is just not wired to anything.

If the circuit breaker is on, the power from the generator will go to either a “J” box or an automatic transfer switch (ATS). From what I can see on video walkarounds is the shoreline cord is in the back driver side compartment and has a quick connect on the side wall of the compartment. I cannot see a separate “J” box. Here is what one would look like.

Since it looks like a quick disconnect, which is a twist-on plug, there is only one outlet box in the compartment that would look like this.

This is an electrical compartment in the 2015 Thor we have been working on, and it is a 50-amp service. However, you can see the shoreline cord is connected in the upper left to the junction box with a similar quick connect.

What the ATS does

This most likely has an ATS, which means the power from the generator comes to the ATS directly and the outlet for the shoreline cord is also wired there. When the generator is running and power is coming from it, the ATS will default and switch internally, allowing power to flow from the generator to the distribution center. Once the generator stops, it switches to the shoreline outlet.

Use a noncontact voltage tester

The ATS can become defective and not switch, so I would verify that power does get from the shoreline power to the distribution center first, then unplug the shoreline power and start the generator. Use a noncontact voltage tester to verify 120-volt power is coming from the generator to the ATS.

This will verify 120-volt power is coming from the generator and getting to the ATS. Next go inside and, again without the shoreline cord plugged in and the generator running, use the tester to check for 120-volt power at the distribution center. You will have a main breaker on the panel that is 30 amps, and several individual 20 amp breakers for appliances and outlets.

If you do not have power here and there was power at the ATS, either your ATS is defective or there is an open circuit in the wiring from the ATS to the distribution center. But if there is power at the distribution center, check the main circuit breaker as well as the individual circuit breakers to verify they are on. If you have power to the distribution center but not to the appliances and outlets, your main breaker most likely is defective.

 You might also enjoy this from Dave 

Why did RV’s lights and fridge stop operating on generator?

Dear Dave,
Recently I turned the generator on and, like always, it came on, but my inside lights, fridge and all did not come on. I plugged in my shore plug, and all came on. What could be the issue? Any troubleshooting I can do? This has never happened in my years of owning it. Doesn’t appear to be blown breakers or fuses on hallway floor panel. Help. —Janis, 1995 Rexhall Aerbus

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberg
Dave Solberg 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. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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Michael Galvin
1 month ago

When my generator doesn’t work, it’s because I forgot to plug in the shore power cord to the generator panel down in the electric bay.

Dave Telenko
1 month ago

Hey Dave
As a side note & nothing to do with generators! Dave you have a pic of the electrical compartment on a 2017 Thor that you’re working on, in that compartment it appears there is a segmented flag pole with an LED light on top, any chance you have some information on it?

Neal Davis
1 month ago

This has happened a couple of times with our new (since 7/2022) DP and we had tripped the breaker on the generator both times. We are updating our pre-departure checklist to preclude it (at least because of us failing to power-off stuff before departing).

1 month ago

The issue can also be within the genset itself. We had no power from the genset while at a rally in Perry, GA. The generator would run fine, but no power output. I don’t remember what internal part it was, but an Onan facility in Nashville found and fixed the issue quickly. Back in 2002 the fix was around $80. Nowadays they probably wouldn’t even diagnose it for that!

Parson Pete
1 month ago

I have been twisting wrenches for some 60 odd years so thought I knew a lot about gasoline powered engines. Before going on a trip to the ice fields in northern Canada I serviced my Onan genset; new plugs, fresh gas, cleanup, etc. It ran like a top. However, once “up North” when I started the generator I had no electricity in the RV. A little t/s determined that the ATS was not switching to the gen side, due to a blown diode in the box. H-m-m-m! What I later learned is that while a car mechanic may advance the throttle position manually to check smooth operation at higher rpm, not a good idea on a generator. The higher rpm also meant higher voltage that blew the diode in the ATS. Back in the states it was a quick and cheap fix ($25 for a new board) but it sure would have been nice to have electricity while in Canada.

Bob p
1 month ago

We had a 2002 Mountain Aire was new to us, on our first trip returning from KS we stopped at a friendly KMart that allowed us to park for the night. Upon starting the generator DW said only half the motorhome is working. Getting out the owners manuals, yes I said manuals because Newmar supplies a manual for everything on or in the unit, I discovered the two circuit breakers on the generator. Upon checking I found one breaker tripped and the other on. Resetting the tripped breaker DW now had power to prepare our meal, and that gave me more respect for Newmar. We sold that unit regretfully after we had done everything to make it ours, we still regret that mistake.

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