Tuesday, December 5, 2023


Can I “exercise” my generator while plugged into shore power?

Dear Dave, 
I am trying to figure out if it is OK to start my generator up on my toy hauler while it is plugged into 50-amp service shore power. Since I bought the trailer in Dec. 2021, it was plugged into a 120v outlet for the first two months (Jan. and Feb. 2022), just to charge and have minimal power. As of mid-Feb. 2022, I’ve been living in the trailer at an RV park while working and have barely even used the generator at all.

I am concerned if I don’t run the generator for a while soon it could cause problems with the battery or the small amount of fuel the dealership had placed in it. I don’t mind having to unplug the trailer from shore power and run the generator for a couple of hours. I’m just curious if it needs to be unplugged, since I would normally boondock with my old 2001 toy hauler and pretty much ran generator only. Thanks. —Ronnie, 2021 Keystone Raptor 423 Toy Hauler

Dear Ronnie,
I assume from your comment about the small amount of fuel that your generator is a gasoline model. However, you did not mention if it is a portable or onboard generator. Either way, it is recommended that you run your generator every 30 days under load to not only lubricate the interior components but also burn off any carbon or varnish.

Earlier I posted a question and answer about winterizing a generator and not being able to get to the rig every 30 days. You can read the post here.

Recommended Onan procedure

Just as an overview, there is a procedure Onan recommends about filling the fuel tank and adding a can of OnaFresh Fuel Stabilizer, detaching the fuel line and running some of the additive through the carb, and spraying a fogging product in the cylinder as well.

However, back to your question about starting the generator and being connected to shoreline power. If you have a permanently mounted generator, it either has an automatic transfer switch or a “J” box. This is what an automatic transfer switch (ATS) looks like.

The power cord from the generator is wired directly to the box and the shoreline cord comes out of it. A power cord is wired from the ATS directly to the distribution center inside your rig. When the generator is started, the ATS identifies power coming from the generator and switches internally to allow the power to flow from the generator to the distribution center, which shuts off anything coming from the shoreline cord. If you have an ATS, even if you are plugged into a campground source, the power will come from the generator and not from the cord until the generator stops, at which time the ATS will switch back to the shoreline cord.

If there is no ATS box

However, if you do not have an ATS box, then you would have a “J” box that looks like this.

This is basically a manual version of the ATS, as the outlet on the right side is wired to the generator so you have to manually plug it into the outlet to get power from the generator when it is running. And you have to manually unplug it and plug into a campground source to provide power from there to the distribution center.

In this type of setup, if you are plugged into a campground source and start your generator, the power just goes to the outlet and does not come into the coach so you will not overload the distribution center with power from two sources.

 You might also enjoy this from Dave 

Ask Dave: Can I start my generator when RV is plugged into shore power?

Dear Dave,
I own a Class C motorhome. Can I start the generator when I am connected to 110v AC power at a campground or at home? Or will that create a problem? Thank you for your help. —Sam

Read Dave’s answer.

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

Read more from Dave here


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Dave Solberg
Dave Solberghttp://www.rv-seminars.com/
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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Ron L (@guest_215045)
11 months ago

The poster was asking if he can start his generator while plugged into 120v outlet. He really means if he can start his generator while plugged into a 15amp outlet as even the outlets in his 5’ver are 120v. All outlet powers are determined by their amperage, as all outlets are 120vac. I’m surprised that Dave didn’t mention this.

Last edited 11 months ago by Ron L
Bob (@guest_215057)
11 months ago
Reply to  Ron L

That’s the second entry in the post. “You might also enjoy this from Dave”.

Original posted question says he is plugged into a 50 amp shore line.
Two different scenarios.

tom (@guest_215004)
11 months ago

I installed a fuel cutoff on the genset fuel line. If used, when finished, I turn the fuel line off and run the genset carb dry. Nothing remains to dry out.

Kasey (@guest_215003)
11 months ago

If you have a J box and don’t unplug from shore power and plug into the Jbox when you run the generator, you’re not going to achieve any load on it. Fine for running it, but the recommendation is a load on it for exercise.

Dna (@guest_215007)
11 months ago
Reply to  Kasey

Exactly. Is it just too difficult to unplug from shore power and run the generator for 20 or 30 minutes? When ours is in storage we start the generator and run either the AC or a small oil filled space heater to provide load.

Cee (@guest_215061)
11 months ago
Reply to  Kasey

I must be misunderstanding you… I can’t be plugged into both the J box and the pedestal at the same time because I have only one shoreline.

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