I have a 1947 house w/ a main electrical panel (see pic below; in order from top to bottom the breakers are: 125 amp; 20 amp; 100 amp service disconnect; 30 amp (garage); 20 amp). There's the main service disconnect, then 4 circuit breakers---these lead to 3 places: An electrical panel on the main floor, and electrical panel in the basement, and an electrical panel in the detached garage. I believe the house only has 100 amps running to it in total, seeing as the service disconnect is rated at 125 amps and the house is so old.
Right now the garage has a 30 amp capacity (30 amp breaker w/ a 12 gauge wire). I'm wiring up a small workshop that's in the garage and would like to increase this to 60 amps if possible. However, I'm having a hard time determining if I can safely just swap out the breaker on the main box and run a higher capacity line. I do realize that if I were using close to 60 amps in the garage I'd be using over half the total capacity of the house and could risk setting off breakers if enough power was being used in the house, but my real issue here is whether or not the panel itself would be able to manage a 60 amp breaker along w/ everything else in the first place.
Anyone here know how to look at this correctly?
1) I believe that 10 gauge wire is the correct wire for a 30 amp circuit, so it seems your breaker is already to big today for your existing wire.
2) A panel rated for 125 amps, which has a 100 amp breaker should have no problems as result of a 60 amp breaker being install (you could only trip the 60-amp breaker if you overloaded the garage or the 100 amp main breaker if all of your circuits together overloaded it). The main breaker will protect long before the panel itself was in danger from too many amps flowing through it.
3) Make sure that your garage sub-panel can handle 60 amps and if it has a main breaker remember to adjust that one as well.
4) Despite my comments and questions below regarding code . . . I googled Challenger electrical panel (for only a few moments) and it was enough that if one was in my house I would be concerned. It seems they can have some serious risks (see:
http://inspectapedia.com/electric/Challenger_Electrical_Panels.php) From one discussion it seems that this may have been due to faulty breakers (
https://www.nachi.org/forum/f73/challenger-panel-rejected-tower-hill-86547/) and there are approved breakers for the panel (file:///Users/WaggleDance/Downloads/UL%20listed%20C-H%20breaker%20used%20with%20westinghousebryant%20challenger%20panel%20load%20center.pdf)
If I were in your position, I would assess the condition of the panel before going any further with your current project, depending on you skill and comfort level that may mean calling in a professional electrician.
The double breaker in the middle is the main service disconnect. The oversized, 125 amp breaker on top serves no purpose, the main would trip first. As for upgrading the garage service from 30 to 60 amps, yes you can do it, but I wouldn't recommend it. That type of breaker panel is no longer code valid, replace it outright with a 150 to 200 amp rated panel if you can. If you do it anyway, be aware that you have to upgrade the copper wiring from the panel to the garage as well. But the garage having over half of the main panel's power capacity is irrelevent, there is an expectation of non-coincidence of demand. Said another way, if you are in your garage using high power for short periods of time, and the main house is mostly using light loads such as lighting, you can make it work.
I am not sure how it is with panels, but with many other aspects of a home a change in the code (i.e. no longer meets code) are grandfathered and do not have to be replaced; not meeting current code does not mean that it is inherently unsafe. Like I mention above, this panel could have safety issues, which is entirely different than not meeting modern code.
Actually, looking at it again, that's type can have it's main breaker on any set of slots; so the top could still be the main disconnect, but then the sticker should have been moved. Again, this type isn't code for a main panel anymore. You really should consider calling an electrician to replace it.
For my own knowledge, how did you determine that the main breaker can be anywhere? From looking at the diagram in the first picture it indicates the main is located between 8 and 9 in the middle of the panel where the sticker is placed.