For starters, this is in an RV in the United States. But the 120v electrical system is identical to a home just on a smaller scale. For specifics, it's a 50amp RV which is 110/220v split-phase. We can completely ignore the 12v/battery side of RVs for this discussion.

Because it's an RV, let me give a tiny bit of background. I have 2 sources of power - either shore power (aka plugged into a campsite) or generator power. These both feed into an automatic transfer switch (ATS).

The output of the ATS goes to my main distribution/breaker panel.

Main breaker panel

I also have a secondary panel:

Secondary panel

I initially thought that this secondary panel was fed from a breaker in the main panel. Turns out, it's not connected to the main panel whatsoever. It's actually fed directly from the automatic transfer switch.

Current setup

This will make you weep, but here's the ATS. The input enter from the bottom of the picture and output through the top. The orange 10/2 wire is what feeds the secondary panel.

Automatic Transfer Switch Wiring

Due to some future upgrades (that do involve the battery system + inverters), I'd like to make this a proper subpanel that is fed from the main breaker panel instead of the ATS. But, as you can see from the first image above, I'm out of space. My options are:

  1. Replace a breaker with a tandem breaker and feed the subpanel off of the tandem
  2. Move the water heater/20 amp breaker to the subpanel and using that now freed up slot

I'm leaning towards #2. But here's where my actual question is... how do I determine the size of breaker that should go into the newly freed up slot? Is 30amps enough? Or do I need to put a larger breaker there (and a matching one in the subpanel and upsizing the wire based on length + breaker size)?

The final product would look something like this (but obviously, with a potential different sized breakers + wire size):

Rearranged installation

  • Who is the manufacturer of the panel and does it have labeling stating the correct breaker types to use? I note a dog's breakfast of HOMeline, Siemens and Eaton BR. They are not compatible with each other. Jul 6, 2022 at 19:26
  • I'll check. I'm not sure which specific breakers each needs.
    – Doug S
    Jul 6, 2022 at 19:28

2 Answers 2


So this one turned out to be short and sweet and did require a little bit of RV knowledge. Since I'm gutting the 12v system and replacing it with 48/12v step down converters, I don't need the Power Converter breaker any longer. I'll pull the wires for that, cap them, and can then put a 30amp breaker in its place. That'll feed the subpanel.

And 30amps for it should be plenty fine, especially considering I opted for a combo washer/dryer instead of stackables. The dryer breaker isn't being used and if I do reuse it, it'll just be for some tech cabinet stuff at very minimal amperage (1-3, I'm betting).

  • Please continue to bear in mind Harper's advice to make sure you're using the correct breakers for your panel - replace the foreign ones immediately no mater the cost. You cannot (safely) mix and match breakers in a panel. They won't fit properly and have a high likelihood of eventually failing and resulting in a fire. If that fire happens when you're on I-80 in the middle of Wyoming, say goodbye to the RV because by the time fire services get there, they will only be able to give you a lift to the next town and call in a wrecker to haul the remains away.
    – FreeMan
    Jul 7, 2022 at 14:04
  • Thanks for explaining his comment because it was largely lost on me. Those mix and matched breakers came from the factory this way (doesn't make it right, I know!). Interesting to see/hear how it's a bad idea.
    – Doug S
    Jul 7, 2022 at 15:34

There are 2 standards for RV’s 120v 30 amp and 240v 50amp.

The size breaker should match how you want to rewire, yes you can maintain the same generator and use the larger service.

The size breaker feeding the unit should be either 30amp 120 OR 50amp 240 by maintaining the size and type of electrical you will be able to plug in at RV parks where if you changed this and did not use 30/50 you would not be able to plug in or not allowed because of non standard equipment.

  • I'm sorry but that doesn't answer the question. I know it's a 50amp RV. I have a 50amp main panel in the RV. It's this subpanel that I'm trying to determine its breaker sizing that I need help with.
    – Doug S
    Jul 6, 2022 at 20:07
  • Sure it dose any RV pedestal will have exactly the same as I mentioned so it will be either a 50 amp 240v or a 30 amp 120v those are the choices not just what RV parks offer but it matches the code requirements also.
    – Ed Beal
    Jul 7, 2022 at 4:09
  • 1
    I’m not interested in changing what is coming into the camper, that stays at 50 amps/240. I want to pull this second panel in to being a subpanel under the existing main panel and was hoping for guidance on how large of a breaker it should be protected by.
    – Doug S
    Jul 7, 2022 at 13:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.