I'm hooking a 100A service panel to my meter pan. There is the 100A disconnect panel on the right side that feeds the little house, I'm installing another panel on the left side to service my barn, an approximate 150' run. Feed to the barn is 3 conductor direct burial cable. Two of them look like 00 AWG, guessing, but the wire is a good solid 1/2 inch across. The 100A breaker terminal will fit, looks like, #4 at best. Is there is "reducing" type terminal that will allow me to tight fit the 00 AWG wire and then insert into the breaker?
Electrical – How Do I Connect 00 AWG Wire to a 100A breaker
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Spaces vs Circuits
First let's explain the 8/16 thing, or "8 spaces but 16 circuits". At some point, panel manufacturers developed what I (alone) call a "double-stuff" breaker, which crams 2 breakers into a single space. This is intended to solve crowding problems in too-small panels.
photo source: Home Depot
Relying on these, marketing called their boxes 2X-circuit (X-space). Around 2014 they mysteriously stopped doing that. Recent NEC changes required AFCI or GFCI breakers on damn near every circuit... AFCI and GFCI are not made in double-stuff breakers.
Your 16/8 service panel is a legacy of that bad labeling. You have an 8-space panel, intended to replace an 8-space fuse box.
Panel space is dirt cheap. Go nuts.
You are dreaming of a 16-space panel. And even that is dreadfully small and you will find it rather limiting even with 100A service.
The practice of many electricians is to give you the smallest panel possible. That's first, to force you into more subpanel work if you expand further (more money for them) and second to save themselves $20 in part cost.
The cost of a larger panel is trivial tiny compared to total project cost. It is very correct to be extreme. Please spend an extra $100 for a 42-space panel, unless you just can't make it fit. Honestly I'd go 60-space. Not least, those larger panels are 225A-ready.
You never know. You might do a kitchen remodel and go hey, I'd like a separate circuit for refrigerator done microwave done dishwasher done disposal done 3 outlet circuits done. You have the space.
When you buy a PC, do you really calculate your needed hard drive space and buy just what you need... Or do you just buy the big 3TB drive? Of course you do. Same thing here.
More work to do at the meter
OK so the power company says their side of the cable is 320A. If they say so.
They say their meter is 320A. If they say so.
But your meter housing is not 320A.
To support more than the listed 125A, you will need to upgrade your meter housing. There's no question of that. That's your equipment and you have to pay for it, probably, unless your power company does something different with cost sharing.
You won't be able to replace parts of it, you will probably even have to replace both sides of it as a single unit. However it is very nice to have your main breaker in the meter. It means you can fully de-energize your main panel, which makes it safer for you to do yourself.
The 320A may be shared
Since it's multi-unit, the power company provisioning 320A makes more sense. Trouble is, this 320A service is probably shared between both units. So it's not as much as you think.
You really need to talk to your power company about what they consider this "320A" to be. It may be a relabeling of what other power companies call 400A service. So they may be willing to feed two 200A panels, or 100/100/200. This is a conversation you can have only with them.
More food for thought is sub-metering units, and separately metering common spaces. The new thing in rental properties is to have one main meter and the landlord has sub-meters per tenant. Many landlords prefer (and some law requires) commons space usage to be on a separate (sub) meter, i.e. heating, yard and commons lighting, anti-freeze pipe wrap or roof/gutter heat, coin laundry, Christmas decorations etc.
The breaker in the main panel is the ruling breaker, as it protects the wiring between panels. A "main breaker" in the subpanel cannot protect that wiring, so it serves only as a shutoff switch, AFCI or GFCI if equipped. ** Therefore it doesn't matter if the subpanel breaker is larger than the main panel breaker. There is nothing wrong with this and it is often mandatory.
If you want a shutoff switch (or master GFCI or AFCI) in the subpanel, select a subpanel which does that, i.e. a "main breaker" panel rather than a "main lug" panel. Main breakers make affordable shutoff switches.
Note that such a shutoff switch is mandatory when the subpanel is in a different building.
What if you have a main-lug panel? Can you just install a regular breaker of usefully large size, and backfeed the breaker? Not quite. Anytime you backfeed a breaker, it must be bolted down. (you can imagine how that rule got written.) You will need to either
- already have a panel type where breakers bolt down (Siemens, QOB, Pushmatic)
- bolt down the breaker using a listed method (which presumes the panel provides the right bolt-downs, and a breaker with the right holes/brackets)
- add an external shut-off switch
- swap the panel out for a main-breaker panel
- or if legal, do without a "main" breaker.
Edit: Here's an interesting listed method for Siemens snap-in panels to bolt a breaker down. This gen/utility interlock bolts directly to the breakers, and locks them together in a way they can't rotate to snap out -- thus satisfying boltdown. In your case, you're only after that, so the other breaker position is wasted. Do not use Siemens breakers on anything but a Siemens panel ***. I hear they'll snap in, but at wrong clamp tension etc.
** Hypothetically if you provided a 100A feed on #1AL wire to a 60A subpanel, the 100A in the main breaker would protect the wire, and the 60A "main breaker" in the subpanel would protect the subpanel. But that installation would violate diy.se's advice of "get a really big panel". Also the 60A wouldn't necessarily trip first.
*** Siemens does make breakers specifically designed to go in a QO panel. (why??) Those are for QO panels only, don't even use them in Siemens panels.
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Best Answer
Short answer - you don't. I'll echo what others have said - don't guess - find out what you have. Size and whether copper or Al. Find out if you can make splices in your panel per local code and (if allowed) splice down to the correct maximum size that the breaker will accept. Tester says it correctly - 4 wires needed -2 hots, a neutral and a ground, but the ground wire may be a size smaller than the required "hots". ALSO - once finished, will you have two separate services both feeding off the meter pan? It sorta reads that way. I do not believe you're allowed to "Piggy back" wires on the meter pan and in my locale there must be one main to turn off everything. So- one main panel to feed two sub-panels. Draw and post a diagram if you can take a picture of it. Indicate hots in red and black, neutral in white and ground in green. This is the level of detail you need to understand it, if you do this as a DIY. About a year ago, I took on a sub-panel and ran flex metal cable throughout a new shop. I researched the heck out of. It was not that hard to learn and obey all safety rules, whether or not you have code enforcement.