Major update 7/16
Thank you all for your helpful replies and encouragement! I wanted to update everyone on where I'm at with this project.
Intentions and use case for adding a subpanel
To answer the intent question brought up in a couple replies, my immediate intention is simply to be able to allow simultaneous operation of two woodworking machines (one is a dust collector) on 120V and/or 240V. Ergo, two 120V branch circuits and two 240V branch circuits, right? But beyond this, if I'm putting the effort into installing a subpanel in the garage, I would like to account for the possibility of an electric heater, ductless mini split with heat pump, and /or electric car charger in the future. What do you think? Is this reasonable? Do I need to account for anything else? Oh, one more thing. I do have a goal of building a sawmill with, say, a 7HP, three-phase motor on it. I do not intend to weld or use a plasma cutter here, but that could change or could happen under a future homeowner.
Note that right now I have only 100A main service installed in a 1980s CH7CC Cutler Hamer Loadcenter. I have no intentions whatsoever of getting an electric car in the next few years. Furthermore, with only 100A service, it is unlikely I will be doing electric heat. As I said, while I want to allow for future possibilities, my immediate use case for the foreseeable future is literally just running a saw and a dust collector at the same time. I currently have a 9A 240V dust collector and a 15A 120V table saw. It is likely I will get a 3HP bandsaw in the future, and I might change the table saw to 240V if not install a 3HP motor.
Before I apply for my permit and proceed with the project, I would like to get your feedback on three alternative options to a garage subpanel:
Garage subpanel alternative #1:
First, after talking with my power company, it appears there is the possibility of relocating the meter and service entrance to exterior wall of the garage...on the other side of the house. I was told this is done by an electrician and/or the homeowner because the pad-mounted transformer is member owned, and it is common for a homeowner to do the trenching. The upside to this is the current main could be fed as a subpanel and, I believe, ultimately phased out, which would be nice because it's in the wall of a finished basement living space.
Here is a two-minute, narrated 3D animation outlining this option:
Is this ridiculous, or is it practical if not a good idea? My main concern is the time and effort it would take to do this. Furthermore, I am not sure if wires can be spliced and rerouted to the garage over time such that the current main can be phased out. While I like the idea of this, I know of only one (possibly) legal way to do it, and I doubt it's designed for splicing literally every circuit in the house. The three 240V circuits could just be rewired entirely since they're so close. If there is no possibility of phasing out the current main without rewiring the entire house (or at least the first leg of each circuit), I don't think this is practical to even consider.
Garage subpanel alternative #2:
Second, I can either have the main panel and service upgraded to 200A, or I could do it myself. If a subpanel is to go in the garage primarily for just operating two 10 - 15 amp motors at this time, I do not believe the main service needs to be addressed at this time.
That being said, if the main were already 200A and had more than two open breaker slots, would you instead simply run four branch circuits from the main to the garage, or would you still install a subpanel? The nearest garage wall is exactly 20' away and up one level.
Garage subpanel alternative #3:
Being that my main panel is a) in basement living space with finished walls and ceiling, and b) it has only two open breaker spaces, should I instead consider putting my subpanel in the basement utility room and running the branch circuits to the garage from there? It is located on the other side of the garage back wall and down one level, and it has 5x5' of room in it, half of which has furnace ducting protruding 1' from the ceiling and a sump basket in the floor (though no pump...yet). The other half has a drywalled wall that would make the required clearances for a panel install, I believe. In other words, would it be better to run branch circuits to the garage and then have this panel accessible for future work on the house, e.g. living room can lights, kitchen remodel, and/or house addition, all of which would occur above the main basement area, which has a drop ceiling? Or should I not worry about it now and just install my subpanel in the garage, later having to run a circuit or two either to the garage subpanel or to the house main (if it is even upgraded and thus has more spaces)?
Here is a two-minute, narrated 3D animation outlining this option:
Attached is a photo of what would become free space if I removed the shelf, screens, and tripod.
General updates, wire selection, panel selection:
In the past two days, I have spoken with both my local electrical inspector and my local building inspector. Both were friendly and helpful. I am also ready to submit my electrical permit application at any time, which will be approved the same day so that I can start work quickly.
- The electrical inspector did say that yes, he will tell me what he wants to see if I'm off on a couple things, though he did say that I am supposed to know what I need to do. But that's why I'm here, right? He was friendly, though, and even said he would stop by to take a quick look after I've just started to make sure I'm on the right track, which is very kind of him.
- The building inspector said it's perfectly fine to mount a subpanel in a drywalled garage wall that has the residence on the other side because the panel closes the hole cut in the wall for it. No concerns whatsoever.
What kind of feeder wire should I use for this? Again, it's 20' exactly through the joists (will have to drill holes, as the run is perpendicular), and then <10' vertically in total...so less than 30' for sure. I was originally going to use 6-3 Romex, which can be purchased locally for $1.63 per foot. Alternatively, the second of two nearby suppliers with whom I spoke suggested #2 SER cable @ $1.42 per foot "because it's good for 90 amps versus only 50 or 60." Until hearing this, I had thought 6-3 was completely the right choice. As I am truly trying to consider future use and expansion, e.g. electric heater or mini split AC, electric car charger, or welder or similar, I want to take the time to do this right the first time. Is that fair?
For subpanel size, given what I've outlined above, I am thinking of going with a 16-space Eaton CH unit, $50 for panel + $20 for cover, because my main is also CH. Thoughts?
Are there any specialty or unique tools I will need for this job aside from a heavy duty drill, auger bits, and wire strippers?
Finally, am I correct in understanding that when the main breaker is off, nothing in the panel is hot except for the service entrance conductors themselves and where they connect to the main breaker? The hookup sounds basically the same as a standard breaker, which I have done before, aside from an additional conductor. I'd stick a normal breaker in there without giving it a second thought. Not sure why I've made a big deal about this install
