If you are having issues with drilling the corner, realize that you can make the job significantly more possible with an ordinary drill if you don't try to hold it level - shift the wire up or down a few inches as well as taking it around the corner, and the hole becomes much easier to drill.
As for your question about the approach using conduit, that's going to depend on the LAHJ (local authority having jurisdiction) a.k.a. "the building inspector", if you are subject to inspection. Generally better to ask them first, than to try and convince them that the internet said X would be OK...what is acceptable in one local area may not be in another, and in some cases what's acceptable in the same area will vary with inspector (probably shouldn't, but often does, even so.)
Per the calculator here[http://www.electrician2.com/calculators/vd_calculator.html], 150 feet at 100 amps on 10Ga copper would be 15.5% drop - not the least surprising given that 10Ga is 30 amps in normal use and that's a long run.
- 3AWG copper is 3.1% drop - not quite kosher, but pretty close.
- 2AWG copper gets it down to 2.4%
- 3AWG aluminum is 5% drop.
- Aluminum has to be 1/0 (0) gauge to get below 3% drop (2.5%).
1" schedule 40 Conduit is not adequate to run a service with any of the sizes that will actually carry that load. I'd suggest 2" schedule 80 so that you could run it on aluminum wires, since they will cost a good deal less than copper, even at the larger size, in general. Schedule 80 only costs a little more than schedule 40, and is thicker/more robust. Since you already have it, run the 1" conduit in the same trench and you can use it for network, telephone, intercom or the like.
In a quick look at my local prices from vendors that publish prices...(there are often better prices from other vendors, but the relationship between Cu & Al is less variable.)
- adequate 2Ga Cu $1.79/ft
- not quite adequate 3Ga Cu $1.39/ft
- overkill 2/0 Al $0.98/ft
- and adequate 1/0 Al $0.82/ft
If you buy a separate ground wire, and upsize the conduit to fit it, there's also a 4/0 4/0 2/0 aluminum wire (twisted together, but not jacketed) for $2.09/ft, or less than 3 individual 1/0 wires. A better supplier might have a similar product with all 4 wires at a similarly attractive price. Depending on insulation type, that will still fit in a 2" conduit (or need 2-1/2 for other insulation types.)
None of this assesses whether your service into the building will carry the additional load, either. You may need to upgrade that before proceeding.
Both compressors (moreso) and tablesaws are hard to start - and both benefit from being run as 240V loads if possible, since they'll draw less current that way.
Best Answer
25 feet is no big deal for voltage drop. We start worrying about 70-100'.
You don't need a 20A switch unless you're switching 20A of lights. For a common household light, a regular switch will do.
You're speaking precisely about wire type, i.e. NM-B, but that's absolutely the wrong wire for that job. NM-B can't go outside. I say "wire" instead of "cable" because you are better off using actual wires in conduit, which is to say THWN-2. If you want to staple cable to walls at the ends of the conduit run, have the conduit end in a junction box, then use the junction box to splice between your NM (outside conduit) and THWN-2 (in conduit).
You can get multiconductor cable similar to NM that is rated for outside, but it's more expensive than THWN and it will be much harder to cram down a conduit.
Make sure you bury deep enough, 6" for rigid conduit, 18" for other conduit.