Hello BenTripin,
Thanks for posting your sub install. This is good info for anybody who wants to get rid of the hazardous extension cords and power strips in their grow room & bring in some serious power.
I certainly don't want to bash your work and I know that you posted this info with the intention of helping your fellow indoor gardener but I do want to point out a couple things in addition to what has already been said.
I'be pasted a copy of one of your pic's below & inserted an orange arrow over what I believe is the bonding screw that should connect the neutral bus to the enclosure if this panel were being installed as service equipment. While your ground bus MUST be bonded to the enclosure, the neutral bus cannot be bonded in your sub panel installation. Just make sure and remove that green screw and connect the ground bus to the enclosure and you're good.
The other thing is that your Romex 6-3 w/gnd is rated for only 55 amps.
See NEC table 310.16:
If you were to run some 6ga THHN in conduit you could increase the rating to 65A. See the de-rating table too as you must de-rate the ampacity of the wire as the temp rises (91% @ 87°F...)
Once again, I don't mean to knit-pick your work -Just some constructive criticism aiming to help anyone else out there who might be doing a similar improvements in their grow-op.
Anything that helps people get rid of extenion cords & power strips with HID ballasts connected to them is a good thing.
But, to all those considering a similar project, if you don't have electrical experience you should hire an electrician or enlist the help of a trusted, competent friend with some real-world electrical experience -Installing a sub panel in your home or building is not the type of job that you should take on for practice! If you need information don't hesitate to ask for help. There are people here and on other forums on the web who are willing to help. I get calls and emails all the time from people I don't know -even people who have bought equipment from my competition have asked for help! And I'm happy to do it -If I can do some small thing to maybe prevent somebody's house from burning down I will do anything I can!
Here are a few links with electrical info some folks might find useful
240V receptacle & panel wiring:
The 240V system explained:
Why do I need four prongs/four wires (my stove only has three!)
Timers, Relays & Contactors:
Hope this info helps somebody out there... DW