Electrical – Elecrical panel box. Does it need a cover

This one popped up for some reason, so I'll edit in some new thoughts.

Corroded or arcing power feeds are "burn your house down" serious business. Fix immediately! Aluminum feeder wire is fine stuff, but you do need to use the anti-ox goop, and torque it correctly. Many electricians in the 80s and 90s did not get the memo. Nip it in the bud fast.

Likewise corrosion (read: arcing) on breaker contact points is absolutely unacceptable. Catch it early and you may be able to save the breaker space, otherwise that's a dead space in your panel. The #1 cause is using the wrong brand of breaker. Brand X breaker won't engage Brand Y buses with the correct contact shape or clamping force, causing the arcing.

If the panel is a goner, swap it. Let me come back to that.

The cable between main and sub doesn't need 2 breakers. It needs a breaker upstream (in the main panel) to protect the cable. A 60A breaker is correct to protect #6Cu or #4Al. At the subpanel, the cable/wire can land on main lugs (provided the subpanel is rated for 60A+) or on the subpanel's main breaker (of any rating - a smaller main protects the panel, a larger main is just a shutoff switch, which you do not need since it's in the same building.) So if the subpanel has main lugs, use them instead of backfeeding a breaker.

One more thing. If the main panel is breakered at 100A, and the cable supports 100A, and the subpanel supports 100A, then the main main breaker protects them all. You don't need any breakers for the sub. You can use thru-lugs or snap-in lugs in the main panel.

With that in mind, back to replacing the panel(s). Talk to the power company and see if your service drop/meter can support 125A. Even if not, you can order a 125A main panel and swap the main breaker to 100A.

See if you can upgrade the main-sub cable to 125A. If so, order a main panel with thru lugs, which will save 2 breaker spaces, and a 125A sub. Voila, no breakers needed, space maximized!

You can also look at the CH or QO panels, which use 3/4" high breakers, so more spaces in the same panel footprint. GFCI and AFCI breakers are available for them.

What doesn't work is "double-stuff" breakers (including GE's 1/2" Q-line breakers). Those are useless as almost all new work today requires GFCI, AFCI or both - and you cannot obtain those in double-stuff. So a "24/48" panel is actually 24, period.

Original:

Wire gauge is decided by what NEC requires (and those are in stair-steps) and what your electrical distributor has in stock.

So with numbers as close as 100A vs 125A, you might get lucky: imagine the original installer found #2 wire was good for 95A, #1 for 110A and #0 aka 1/0 was good for 125A. He can't use #2, the distributor does not stock #1, so he uses 1/0. You get a happy surprise when you aim to upgrade. Hey, it could happen - check. If not, you need to pull bigger wire.

Check the markings on the aluminum conductors to make sure they are stranded and the modern AA-8000 series alloy, which are legal and safe. (NEC 310.106b). The problem alloys from the 1950s are now outlawed, and your distributor won't even sell them.

Your reduced voltage to 108 is more likely to be a problem with your neutral. Poor connections can't drop 12 volts without destroying themselves from heat (volts x amps = watts of heat), more likely your other leg went to 132 volts because of a lost neutral. This is an extremely dangerous condition that needs to be taken out of service immediately because the imbalance can be much worse than 12V, and that will destroy appliances and start fires. If you know where the problem is, but can't de-energize your house now, a short-term work-around is disable one "hot" - doesn't matter which one. Look at how the hot busbars are arranged inside the panel, pick one leg, and remove every breaker which uses that leg. Rearrange as necessary to keep the lights on. At that point, if the neutral fails, the circuits will shut off instead of giving dangerous voltages.

Look for other options (i.e. other brands or suppliers) that will give you more spaces in the panel. You don't want to be forced into using duplex breakers, because - especially when you remodel - you'll be forced to follow current code, and will need more kitchen breakers and GFCI and AFCI breakers in many slots. Those are a lot more expensive as duplex. You can completely fill the panel with double-stuff breakers (in fact, doing so is the basis of their "48 circuit" marketing claim).

Don't buy this at the big-box home improvement stores, go to a real electrical distributor such as Greybar - they tend to be locally owned. They will have better options (eg more breaker spaces in smaller boxes, Homelites are huge), better quality and sometimes better prices. For instance, Homelite is Square D's bottom-tier brand. There's better out there, and it's worth an extra $100 to not have problems like the ones you are having.

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.