Small AC breaker box for a mobile application

slipperysam

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Feb 2, 2021
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I can't seem to find a small breaker box that fits my needs, but perhaps I am misunderstanding how they work. I am very new to this.

I only have 10 AC circuits planned, all 15-20A. I'd like a small breaker box that fits at least 5 tandem breakers to support these in addition to a main breaker for the panel itself, to protect incoming wire between the AC panel and the inverter. However, all such residential boxes I see from e.g. Home Depot or Amazon (Homeline 100 Amp 6-Space 12-Circuit Indoor Surface Mount Main Lugs Load Center) look like "sub panel" boxes that are expected to be fused from a main panel. Such sub-panels would also need an extra grounding bar to keep neutral and ground separated.

Contrast this with the Progressive Dynamics panel layouts here which show that there is a designated main breaker to accept the incoming hot lead from the inverter, and when that breaker is closed, that hot lead is connected to a bus bar which feeds the current through the rest of the circuits' breakers. Unfortunately for me, the panel doesn't quite work; it can be split into two separate 4-space 50a-breaker panels to power 8 circuits per side (but I only have one single-phase 120V lead), or a single 9-space 30a-breaker panel (but I want to power more than just 30a at a time).

1. Am I misunderstanding something?
2. Is there a typical way to take one of those sub-panels and wire it with a main breaker like the Progressive Dynamics one?
3. Do I even need that main breaker? It would seem to me that, without it, the wire between the inverter and the AC panel wouldn't be protected. You could, for example, have 6 awg triplex between the inverter and the AC panel, expecting to support around 50a, then pull close to 20a on, say 4 circuits, causing your inverter output to surge to 80A, much more than the ~ 6AWG triplex could handle. Is this correct? What do people normally do? Links appreciated.
 

slipperysam

New Member
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Feb 2, 2021
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Yeah I've seen those but, it does seem a tad silly to use a $700 dollar AC panel when there is likely one from Amz / Home Depot for under $50.

Maybe I should rephrase my post to a TL;DR:

Does there exist an AC panel with
1. a main breaker (~50A)
2. a grounding bar
3. between 5-10 breaker spaces
4. is not absurdly expensive

If this isn't what you did, what did you do? External breaker between inverter and sub-panel? I just can't seem to find this documented on here but I know everyone that uses AC power on this site has had to do this. If only I knew the search terms :(
 

slipperysam

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Feb 2, 2021
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For posterity, the answer is: backfeed a main breaker. If you wanted to use one of those small breaker boxes from Home Depot that only cost around $40, but they have a main lug instead of a main breaker, just get yourself a single pole 50a breaker that fits in your breaker box, and instead of running the incoming hot lead to the main lug on the bus bar, you feed it to that 50a breaker. There are also "retaining kit" attachments like this to secure the main breaker.
 

rmaddy

Full-time Solar-powered Trailer Life
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Nov 16, 2019
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Now that you have an answer I'll post what I used. I didn't do so earlier because it doesn't quite meet your complete requirements.

First, I'm really curious why you need 10 AC circuits. That seems like a lot for a mobile setup. I only have 3 in my trailer.

I used a WFCO distribution panel. This has two halves - an AC main panel and a DC fuse box. The AC main panel can support either single phase with 3 spaces (up to 6 circuits) for a typical 30A shore power connection or it can handle dual-phase with 6 spaces (up to 12 circuits) for a typical 50A shore power connection.

 

slipperysam

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Feb 2, 2021
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Yeah I saw the WFCO panel, it's similar to the offerings from Progressive Dynamics. Perhaps my build is peculiar? But I have a number of AC uses... The minisplit, water heater, induction cook top, and oven each have a dedicated circuit. A couple 20A outlets in the kitchen, one exterior 20A as well. Then a couple general purpose multi-outlet circuits. I probably could have gotten away with the panel I linked above, which is similar to the AC portion of yours, if I made some of my outlets shore only and put them on the other side of the panel, with the AC-2 output of the Multiplus. But, I'd rather not. And it'll be good to have a few extra spaces available for the future.

For a van, maybe this seems extreme. For my full-time live-in bus, it's luxurious but I wouldn't call it extreme.
 

Rednecktek

Photon Sorcerer
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Sep 8, 2021
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On a boat usually.
2. Is there a typical way to take one of those sub-panels and wire it with a main breaker like the Progressive Dynamics one?

Yes, it's done for most sub-panels installed in houses. Instead of trying to find a small panel with a disconnect, you install a breaker and bring the power into that. Here's a krappy MSPaint sketch of what I'm talking about:

Most sub-panels are designed for 220v split phase and each side of the panel will have its own source, so if you're only hooking up single phase you'll have to get a double-pole breaker and jumper the input between both poles. That way the single phase will power both halves of the buss bar. If you're doing split phase the DO NOT jump those. You'll probably want to leave the Neutral and Ground bars connected (there's usually a strap or bar pre-installed) since that will be connecting up to your chassis. If you want to keep the A/C Neutral away from your chassis, just remove that bar/strap and you'll be good.
 

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HRTKD

Boondocker
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Apr 24, 2020
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Somewhere South of Denver
My WFCO main distribution panel has room for six breakers as I recall. I added a breaker when I put in my LiFePO4 battery bank so that I could easily turn off the LiFePO4 AC-DC converter.

My panel does not have a main breaker. The "main" breaker would be on the campground pedestal, or on my built-in generator. I have caused the generator breaker and pedestal breaker to trip when I pulled too much current on multiple legs (different breakers in the panel).

In my trailer, multiple AC outlets are one breaker. That's the compromise I would suggest you go with. I had to go around and label each outlet so that I knew which outlets were on the same breaker.

At the end of the day, it sounds like you need a 50 amp system, not a 30 amp system.
 
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