Safest way of temporarily working with a failed 4-wire outbuilding subpanel (one missing hot leg, neutral bonded ground on both ends)?

Question

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.

Answer 1

14 years ago it was surely Code to separate neutrals and grounds on the subpanel. Certainly one would never run separate wires and then bond them; that defeats the point of running them in the first place and sounds incompetent. Aluminum wires installed in the 2000s will be large, at least 4 AWG. They probably oversized the conductors because their installer told them to, the idea being to compensate for voltage drop. There are better ways to do that.

Bailiwick

Part of this is a question of bailiwick. You don't get to fix every wiring defect everywhere, you may have to think globally and act locally. If you want to fix the bonding in the barn, that might be "not your bailiwick" and therefore "not your concern". It is irrelevant as to whether your outbuilding is safe.

Since you seem to have permission to control the outbuilding's subpanel, I would test, by unbonding neutral and ground there (after shutting off power). Try using both as a current return for a hefty load like a heater and watch the voltage across the heater. Both will dip and ground will dip further since it's thinner wire, look for a lot more. Just do it momentarily, this is likely to "light up" all your grounds.

What you want is to have a hot, neutral and ground wire that all work, are separate and and are not bonded anywhere in your outbuilding nor in the cable from the barn. And have grounding rods locally, bonded to your ground wire and not your neutral.

You find wire breaks with specialized equipment, typically by energizing or putting a tone generator on only the test wire, and then wandering about with an antenna listening for the signal (or not). It's possible to find and fix it in a day or two if you call in a pro. So get going. Once properly spliced, it will be legal and "good to go".

Questions

Can you do anything about the missing hot? Sure, you can move the other breaker over one space, so it is also landed on the working pole. If this is a 2-space panel that won't happen, but if it's 4-space, should be sympatico. What do you fill the empty hole with? A cover plate, or a breaker.

Is it safe to continue a suspected-damaged cable in service? Not so much, until you are able to get to it and inspect the damage. Not least, a hot could have insulation damage and be energizing the earth around it.

If the barn has a 30A breaker feeding the long run, your outbuilding's subpanel must be at least 30A in rating. 50A is fine. 200A is fine. You are correct, 30A won't damage a 200A panel :) Your outbuilding needs a main shut-off switch in the subpanel and that's why there's a main breaker at all. It is there as a shut-off switch (or GFCI if equipped).

What's bad about a 50A panel is not many spaces, and you go through those much faster than you'd expect. This situation being a case in point, you suddenly need twice as many because half are dead.

How much power do you want?

It looks like they laid heavy aluminum wire. Modern aluminum wire is fine for large sizes. Aluminum's bad rep actually relates to dissimilar metal corrosion, and the lugs are aluminum, so aluminum wire is the right stuff. Darn shame they ran so much so far, though. The voltage drop calculator is telling me for 30A@1000ft, to use 4/0 aluminum cable (at these sizes using copper isn't even stupid.) That's to carry 7200 watts (!!) I hope they didn't do that.

You can also carry 7200 watts with 15A@480V, or 12A@600V. This will allow 8 AWG or 10 AWG copper to be used, respectively, and stay within 5% drop. You have a bumping transformer at each end to kick it up to the higher transmission voltage. This only requires 2 conductors.

Transformers provide isolation, double-isolation in fact, so your panel is no longer a subpanel, it is a new service which absolutely requires its own ground rods, and neutral bonded to ground in the panel. At this point it really is a main panel.

Assuming they've got #1 aluminum in the ground, they could carry 20KW at 480V (80A@240V) or 30KW at 600V, (125A@240V) at sane voltage drop. That's plenty for a full sized house, and only requires 2 conductors. But you'd really want to fix the cable damage/leakage first!

If it's 4/0 aluminum, that could carry 60KW.