After a recent power outage i have serious power issues in my garage. With no load, i get solid 123vac from both channels in the box and a solid 240vac across both legs. As soon as i apply a load one channel drops to approx 100vac and the other shoots up to near 180vac. I have tried isolating individual circuit breakers, but so far only helps minimally and still have no usable power in the garage. It looks to me like multiple breakers were damaged. Is this plausible?
Based on my diy.se reading, you may have a damaged neutral wire to your garage or whole house, which is dangerous. See Loose Neutral or Poor Ground?
You may need to get an electrician to investigate.
The neutral wire balances the two opposite legs of the 240/120 split-phase power system, keeping both legs at approximately 120V despite different loads on each leg. If the neutral connection is weak or breaks, then the power from one leg goes through the loads on it, then through the loads on the other leg, and the different loads can have substantially more or less voltage than they are designed for, with the potential to destroy the devices and start a fire.
This sounds like a lost neutral. Assuming it affects everything on the same power company feed, CALL THE ELECTRIC UTILITY. NOW!!!. This is a serious problem that can affect safety and damage equipment.
The key is "everything". You mentioned "garage". If your power comes into your home (main panel) and from there feeds your garage (subpanel) and the circuits in the house are fine but the garage has problems, then you need to call an electrician as the problem is in the main panel (breaker to subpanel), subpanel or (more likely) the wiring in between.
However, if it is "everything" - i.e., house and garage, or the garage has its own meter, then call the power company first, because they will come for free and an electrician won't, and typically after outages (especially weather-related), the problem is more likely on utility-owned wires/equipment.
See Circuit Breakers on and outlets not working for more information.
First, make sure the house is OK. The "Lost Neutral" symptoms are slippery as can be, and are often mild enough to not be noticed. My cottage complex had an epidemic of appliance failures until my sweetie noticed a Crock Pot not heating well and the toaster being "slow".
But if the house has no trouble, this is a failure of the neutral wire on the feeder between house and garage. 90% of the time, wire failures are at the terminations (ends/lugs).
So, the right answer is to de-energize the feeder, then remove the neutral wire from its lug in the main panel, inspect the lug, inspect the wire end, clean it, refresh the anti-oxidation goop, put it back in and torque it to the panel specification.
And then, go out to the sub panel and do the exact same thing.
Chances are that'll nick it. If not, look for an intermediate splice that failed. If no splices have failed, then you have the less likely but more expensive case of a wire failure inline or underground, e.g. from a rock penetration (which is what you get when you do direct burial in rocky soil without lining the trench with sand above and below).
If you need to replace the feeder, remember that aluminum is a perfectly fine and safe choice for large feeder. The lugs are aluminum anyway.