i purchased a tiny house as an abandoned project, and the electricity was already roughed in at purchase. I'm not an electrician, but all the work on the house seems pretty sound from my research. All the wiring is 12/2, with a an RV inlet (30 amp, 125 v). The panel confuses me, as it has both the ground and neutral on a single bus bar. The breaker is a square D 15 amp tandem, with only a single bus bar. Does this look correct?
This is a total hack job.
It's super cheap, but not even that; there are places money was spent unnecessarily. But the workmanship is a punch-drunk disaster. No one did any research nor asked for any help. The installation is actually dangerous, and could set the tiny-home on fire from an unrelated electrical problem in the facility it's plugged into, even.
Just to breeze you through what's wrong with the panel: #12 on a 30A circuit, no ground bar, lugs double-tapped, missing entry clamp, double-stuff breaker where AFCI may be required, no provision for solar, way too small panel (cannot meet NEC minimums for circuit count). And if it's outdoors: indoor box outdoors, NM cable outdoors, outdoor clamp needed (they don't allow 2 cables), entering a box from the top unnecessarily.
Multi-sourcing and solar
My first thought was that there are four kinds of RV hookups: common 120V/15A (you know the one), trailer TT30 120V/30A, NEMA 14-30 (240V/30A) and NEMA 14-50 (240V/50A) which you see on the big RVs built on bus frames. And then you've got solar on top of that.
And first I thought, "let's get you a line/gen transfer switch". But then I realized those are quite large. Even one that's integral to the panel (like Siemens') does not switch neutral, which is an absolute requirement here!
So what I want instead is to mount a 14-50 inlet (or 14-30 if you are sure you'll never need more than 30A). Right next to that, a tiny compartment where you can stow a short cable with a 14-50 socket on the end. To run in solar mode, you unplug from shorepower, open this compartment, and plug the socket into the inlet. If you're super sharp, you recess all this so you can leave it in while towing.
If your shore power isn't 14-50, you stock a variety of adapters. Most are readily available at RV shops, or a steady hand can make them.
The service panel
That thing actually is a service panel, it's so tiny that it's hard to recognize as one. It won't do. It's a $19.99 Home Depot cheapie, and the worst brand they sell (I think). We're going to spend more like $100 on a proper panel. Panel size is a factor, so we prefer dense panels in smaller sizes. That makes Eaton CH or Square D QO contenders (yes, Square D again, but this time their industrial line) since they pack full breaker functionality in 3/4 the space. (GE Qline goes too far, their 1/2 height breakers can't perform essential functions, other than that it's a fine panel if you use their fullsize breakers.)
As far as spaces, what worries me is that an inspector could come by and require you to have the NEC minimum number of circuits - and also, a few circuits are just a good idea. The former builder used a "double-stuff" breaker to cram 2 circuits into 1 breaker space. Don't count on that, because that inspector may require you use AFCI or GFCI breakers - and those do not exist in double-stuff.
Using the service panel to separate solar loads
You may want to automatically disconnect non-essential loads while on solar. And now is the time to be thinking about it, because there's a clever way to do this for free, right now while we are designing the panel. You see, North American power comes in two 120V "legs". The legs are normally just for more power. They aren't normally assigned different tasks, but they could be. Read my Q&A on double-stuffs, which talks a great deal about how panels are separated into two poles.
So layout your panel so the L1 pole serves loads you do want on solar, and the L2 pole serves loads you don't want on solar. It's important you don't install any 240V loads at all, and avoid using an archaic wiring method called MWBC aka shared-neutral.
After that, the cable I mentioned? You wire up the inverter as 120V, and only connect L1 in the socket.
In North America, that would be correct for the main service panel which is directly after the electric company meter, but it is incorrect for a subpanel.
A subpanel should keep separate the grounds from neutrals and connect those separately to the main service panel. This is to prevent ground loops and the serious danger caused by failure of a conductor. See this and especially this.
Presumably one of the large screw lugs on the bottom is connected to the neutral bar with its four smaller screw lugs, and maybe the other one is also, or maybe the other one is connected only to the metal case. You would have to get instructions for this panel an/or use a multi-meter in resistance mode to determine what is connected to what.
Then determine what are the requirements for bonding the neutrals and the grounds for an RV. The question would be should the neutrals be bonded here or should neutral and ground be separate to the RV receptacle?
If another breaker would be added, a jumper would be used to feed it from the lug on the first. If the lugs are not approved for two conductors, then a single one would go through the first lug and on to the second.