Does the sub-panel seem over loaded? If so, I could keep the water-heater in the main panel and free up space in the panel another way.
Seems reasonable to me. Most of the equipment won't draw anywhere near the overcurrent rating, at least not during normal operation. Motor loads will draw a higher current on start, but you shouldn't have a problem.
I know I need four-strand wire to run to the sub-panel (2 hot, neutral, ground) but copper or aluminum and what gauge?
You can use either copper or aluminum, though I recommend copper for DIYers. Copper is quite a bit more expensive, but it's easier to work with (in my opinion). If you feel confident working with aluminum conductors, you can save some money using it.
I've covered the topic of feeder sizing here, so I won't go into detail. If you're using copper, you'll want to use 3 AWG conductors. If you choose to use aluminum, you'll need 1 AWG conductors.
If you want to run a single cable, instead of individual conductors in conduit. You can buy what's called 3-3-3-5 SER cable (1-1-1-3 for aluminum), which will contain three 3 AWG conductors (hot,hot,neutral) and a 5 AWG grounding conductor.
When I run the wire along the floor joist, does it need to be secured to the joist or can it just hang there and rest on the drop ceiling? Seems like it should be secured to the joist with wire hanger or something.
You'll have to attach the cable to the joists, using 1 - 1 1/4" staples or other approved means. Check the packaging, to make sure they are rated for the size cable you're using.
What are the things about this project that I don't know that I don't know. :) These are the scary things IMO...i.e. the questions I don't know enough to ask.
The cable you'll be working with is thick and heavy, and it's not going to be fun pulling it. You'll probably want a couple helpers, to help you wrangle it.
Make sure all your connections are tightened to the manufacturer's specified torque.
If you choose aluminum conductors, make doubly sure you tighten the connections. And don't forget the anti-oxidant.
Come back a day or two after the panel has been put into service, and tighten any connections that need it.
Don't forget to remove the bonding jumper between the grounded and grounding bus bars.
You'll need clamps big enough for the cable, to secure it to the panels.
should I put a 100 amp breaker in the sub-panel to act as the "main" for the sub-panel? Or is the 100 amp breaker in the main panel sufficient?
You can usually pick up a main breaker panel, for about the same price as a main lug only (MLO) panel. In my opinion, unless the secondary panel is next to; or within sight of, the main panel. You're better served to install a main breaker panel. It simply offers better protection during maintenance, or other work within the panel.
For example. If you turn off the feeder breaker in the main panel, and start working in the secondary panel. Somebody could easily come along, and flip on the feeder breaker. Since you can't keep an eye on the breaker, you can never be sure the panel will be dead. (unless of course you're using a lockout like you should).
If the secondary panel is in a separate building or structure, then you either need a main breaker, a main disconnect, or the ability to disconnect all ungrounded conductors within 6 or less hand moves.
First, the aluminum wire
In the 1960s, owing to a copper shortage, they rushed to market aluminum wire made from transmission line alloys, for 15-30A branch circuits. Electricians used it with common receptacles and switches listed for Cu-only, and in the rush, nothing was properly tested. On top of that, the work was often badly performed because housing booms tend to draw from the bottom of the barrel skillwise. I hardly need to tell you how that went: the things you saw were indeed your house almost burning down, and they were due to arcing. There are two good fixes:
- Tear it all out -- kill it with fire before it kills you with fire.
- Feed it from AFCI breakers, which will detect and trip on arc faults before they melt insulation. Then at leisure move through the house, and either tear it out, or clean up all the terminations of every wire, using CO-ALR rated receptacles/switches and Alumiconns instead of wire nuts.
As a backgrounder, copper has been commercially viable since 9000 BC, aluminum since 1950 thanks to smelting processes which use electricity. Obviously Al arrived in an electrical system long built-out and with pre-existing stock of gear made for Cu-only. The AA-1350 alloy, developed for steel-core transmission lines not small-wire terminations, was also a problem. All done in a rush.
Regardless, it can be argued that Cu is the bad actor because it doesn't have a good elasticity range and likes to work-harden. Al wire on Cu lugs doesn't work, but Cu wire on Al lugs works fine - as seen on Alumiconns, CO/ALR receptacles, and the lugs on your panel. You need to get the torques right because of dissimilar metal expansion/contraction rates. The right torque lets the Al flex and spring back as Cu changes size.
The new AA-8000 alloys are safe for 15-30A branch circuit wiring, but I won't use it because the inspector hates it, the buyer hates it, there's no cost savings, and it's too oddball. Like a lot of people, I start looking at Al for 60A+ (#4-), the larger, the more likely.
Needed service
As I look at your numbers, first, on-demand water heat, awesome. Even better if it's several units near point of use, because then you're not paying or waiting for hot water to cross the house. It's common for all-electric houses in the snowbelt to have 400A service.
I don't understand 4x50A for air conditioning. This seems like both too little and too much for a heat pump, the pump proper doesn't need 50 and the emergency heat usually needs more than 50. Critical issue is which will be used at the same time. If you need to run 4x50A at once, you're gonna need a second service.
Subpanel
I think a subpanel is a great idea and I would go 200 or 225A. Stay with QO if you like, great commercial-tier panel type. I would confer with the power company about where to locate this if it's to be the future main panel for a second service (keeping in mind one option is to put the main breaker outside as part of the meter pan, and feed this as a subpanel). Set it up so you can do both:
- For now, feed it with as you plan, a 100A or 125A breaker and correct size wire.
- later, make it the "main" panel of the second service.
Spaces: You say nine 2-pole breakers (seems low, but alright, 18 spaces) plus you say 15 singles (but I count 18 singles in your panel already with the double-stuff's).
Using double-stuff breakers is bad news, especially on a panel with 3/4" wide breakers. Most circuits are or will require AFCI or GFCI (and you want AFCI on any AL branch circuits). Those don't come in double-stuff, not even on 1" breakers.
Now we're at 36 spaces optimistically, you have 30 now. I would recommend at least a 30 space subpanel but given the small cost delta, I'd go 40 or 42. 40 is not unreasonable for a 200A service.
Existing panel
As far as the existing fat 200A aluminum wires, The lugs are aluminum. I would call the power company, have them pull the meter, inspect them at all ends for deterioration, clean 'em up, use the No-Ox.
Change the meter-panel run to Cu if it's really going to bother you. Copper on an aluminum lug will work if you get the torques right.
What am I overlooking? See the two large wires landed on the neutral lug and dissimilar metals to boot? That is illegal, a recipe for disaster, and a lost neutral can do far more damage than a lost hot. If the stranded Cu cable is your wire to your grounding electrode, that should go to your ground bus. If you absolutely need both wires to land there, then get the correct lug for this, which has voids for 2 wires.
Nope. Try
Src GALCO
It sounds like you prefer running 6 AWG wire. Paralleling is absolutely not allowed, you cannot run two #6's for 100A instead of one #1Al or #3Cu. If you want to keep your heavy-wire runs to a minimum, don't be bashful about putting the subpanel right next to the main panel. That is completely kosher.
For a short run, I'd be inclined to use copper (damn the dissimilar metals) because it will flex easier and be less likely to unclip the breaker.
Best Answer
Your 200 amp service can supply your 150 amp water heater. But will anything else in your house require power at the same time? Such as a microwave, room or house heater, room or house air conditioner, stove or oven? Have you considered using the 24 instead of the 36?