This is actually a multi-pronged question. I will ask it all and split out what I can as needed.
I am renting a remote out building in a rather rustic location on a farm. The power situation here was pretty reckless (as in lots of frayed extension cords running all over the place and mouse eaten wires -- all of which I have removed/replaced with proper solutions) and I am trying to make it incrementally better but have several limitations (the most urgent one being that the ground is about to freeze until spring).
So, there's a subpanel at the outbuilding that was originally fed by a 4-wire hookup from a subpanel at the barn. This was all wired probably 14 years ago. At that point I'm not sure if it was code or not for ground and neutral to be bonded in the subpanel, but they are bonded in both the barn subpanel and the outbuilding subpanel. I know they shouldn't be bonded and that there should also be at least two grounding rods hammered in at the outbuilding for a local ground as well.
Well, at some point this 4-wire bundle (thick, insulated aluminum wires, not sure the gauge or type -- the run from the barn to here is maybe 700-1000 feet), was plowed through and then someone ran a new set of wires from some splice in an unknown location in the field between the two buildings. But whether they wired that wrong or whether it has since failed, there is now only one hot wire coming out to the outbuilding. Since the neutral and ground are both on the same bus (which is completely corroded so I can't quickly and easily detach either), I can't yet tell or figure out how to tell whether ground is broken or perhaps neutral is broken (and the neutral would then be coming in through the ground which is bonded to neutral on both ends, ack!).
So, in summary, here's what I've got coming in:
1.) one guaranteed 110v hot (30amps),
2.) two other wires, at least one of which is obviously carrying neutral back since the power works; they are bonded on both ends so it's hard to figure out which, if either, would be broken;
3.) and one known open wire which is definitely broken somewhere along the way.
While I would like to do so, I can't fix things right; the failed splice probably can't be located before the ground freezes and the owner most likely feels that as long as the lights work the power is fine in her book. Plus, I can't unbond ground and neutral at the subpanel in the barn (I can remove my ground wire if I like from the bar, but can't rewire the whole panel).
So I'm trying to understand what are the critical safety issues and improvements.
I know that:
1.) The ground can be improved with the addition of two grounding rods (I have read at least 6 feet apart -- have to get them in quick as the ground is freesing).
What I don't know:
1.) Can I do anything about the missing hot? I am guessing that it's best to just work with the 110v coming in, unless perhaps carrying the missing leg on what is now the ground wire (assuming it's the proper rating and proper insulation -- at first glance it appears to be the same wire type as the rest of the wires) and dropping anything other than a local ground. I don't know the relative safety repurcussions there.
2.) Is there any real safety issue with having only 110v coming out, other than imbalanced load further back? It is a double 30amp breaker feeding this outbuilding. I plan on detaching the failed leg on the barn-side for safety reasons to make sure there's no live wire out in the field.
3.) What is the safest way to deal with the fact that neutral and ground are bonded in the subpanel at the barn? Is a completely local ground safer than linking up with that bonded-ground? Is it no big deal? I can't modify the barn subpanel in any serious way (other than the wires that have to do with my circuit), but have full control over my subpanel at the outbuildin and can replace and rewire as needed.
As far as amperages if that factors into the degree of danger or the best intervention -- the feed to the outbuilding is originally on a double-pull 30amp breaker. It comes into the breaker box into a double-pull 50amp breaker (that's very bad, right? Or is it irrelevant because it's acting as a cut-off more than a breaker since there's a breaker on the other side). On the other side of the breaker box were two 20-amp breakers (one for each leg coming in), but, of course, only one was working. So I've got 30amp @ 110v coming in, and one 20amp @ 110v currently pulled from that.