Your subpanel needs a main breake--- no, that's not quite right. Your subpanel needs a disconnect switch
. Given the stock of equipment readily available, the cheapest way to get a disconnect switch is to choose a panel with a main breaker, and just ignore the number on the main breaker and pretend it's just a switch
A subpanel also needs grounding rods. One rod will do if it passes a test that requires a $5000 tester, otherwise you need 2 rods >6' apart (most people just go for that).
Wow, that makes a subpanel seem like pain, huh?
However rjniles is right that Code doesn't allow 2 separate 120V circuits out there... but there's a cheat... if one of them is on a switch (from the house), then it's legit.
Otherwise you could follow the multi-wire branch circuit
approach: a MWBC gives you 2 usable 20A "sub-circuits" (one for saw, one for dust collector+lights, solves that piccadillo!) And a MWBC counts as 1 circuit, so that rule is dodged. To do that, take one white wire out of service (cap it off at both ends, don't destroy it) and use the other neutral with the 2 hots. You must tie the 2 breakers with a factory-approved handle-tie, or simply use a 2-pole breaker (which by nature has factory-tied handles. DO NOT use a twin/tandem/duplex/double-stuff
1-space breaker with 2 independent handles!)
Color wise, green and bare must be ground. White and gray must be neutral (and can't be re-marked to be a hot since you are in conduit). All other colors are hot.
Since you are in conduit, you are free to use any colors you want (within the above rules), even purple or pink. They even make color-striped-other-color, like white with blue stripe (blue's neutral obviously). You can't re-mark a neutral to a hot, but you can remark simply for identification purpose: I put blue tape on a white to say "this goes with the blue hot". Easy peasy.
You don't need 2 grounds in a pipe. Circuits can share grounds. THEY CANNOT SHARE NEUTRAL except in the abovementioned MWBC.
If you want a subpanel, the most important thing about subpanels is spaces. Nobody cares what the bus rating or main breaker is (as long as it's enough
). Spaces are dirt cheap when you're buying, and priceless beyond jewels when you're trying to add something. So go absolutely bat-crazy and get yourself a 12, 16, 24, even 30 space panel. Seriously. This means the panel busing and the disconnect switch will be higher ampacity than your feed (currently 20A) and that's totally fine
At some point in the future, I bet you'll pull three #6 and a #10 wire into that pipe, and you'll be glad your panel is 200A-bussed and 125A-disconnect instead of 60/60, because with that #6 you can feed it with a 70A breaker.