I know there is a lot involved in figuring out load, etc, but as a rule what is the max amount of breaker spaces in a modern 100 amp setup? My current GE panel I think is from the 1980's or 1990's and has 20 spaces plus the main breaker at the top. I have two spaces left (yes, they are real spaces not fake). We had the SE cable and meter box replaced right after we moved in here but decided not to upgrade the service/panel to more than 100 amps at the time. Sorta wishing we had, lol. A few more spaces would be golden. Its a tiny house but I did a lot of work rewiring, regrouping, and separating things to bring it up to modern code so I used up most of the spaces. Be nice if we could get a slightly larger panel with the current feed.......

Depending on your box, tandem breakers may be an option. They essentially are two circuit breakers in one slot. Or a sub-panel may be needed. You really should do a load analysis - documenting approximate demand on the system - to properly evaluate where to go now. The sparkies here will confirm.



In the mean time:
HW - service upgrade

In Canada we can get up to 60 circuits in a 100 panel and 120 in a 200 amp panel.

Your panel will list on the door max circuits.
The code until last cycle limited it to 42 circuits in a panel.
It is now more.

A 100 amp 20 space panel can sometimes have 30 or more breakers using the double tap (Twin ) breakers CC listed in his pic.

Each panel has different limits based on the listing of the panel.

Older panels can not have more than 42 breakers.

If panel sticker lists 42, yet current code is say 60, can the OP go to 60? Or must he stay within the panel manufacturer's original stated limit?

Older panels can not exceeded the original limit.

I will see if I can find the UL section.

No need for me...

I wanted to see exactly what it said.

That is the best part about answering questions here. It keeps me up to date and I learn different things.


I never new what incorrigible was?

The specifics on the panel's listing must not be exceeded regardless of the code maximum. The panel label should say something like 20 space 30 circuits IF its listed for tandems. The label should also indicate which spaces accept tandems. There are two types of tandems, CTL tandems that have rejection tabs so they fit in only those certain slots that have rejection tab accepting notches, and non-CTL tandems that fit in any slots. However non-CTL tandems are labeled "for replacement only, not for CTL assembalies" which means they are only listed for older panels that did not have the maximum circuit requirement in their listing. I believe the maximum circuit part of the listing came in the late 60's. Around here there are some very odd local code amendments (local amendments are very common around here), one that has been becoming common (at lease a few suburbs have added it) is requiring all full size breakers. I am not aware of any safety problems with tandems other than false tripping if they are loaded up to their capacity for a long term period. I think some of those local requirements are to eliminate any questions as to if the panel is listed for tandems. Requiring full size breakers for new panels is a good idea, I seen some new installations where the panel was very small and was already filled up with several tandems. But as long as the panel is listed for tandems and you don't have both halves loaded very high for a continuous time (which should be derated if a continuous load anyway) I don't see any problems with them.

"I think some of those local requirements are to eliminate any questions as to if the panel is listed for tandems."

And I think, just because I get all cynical when I'm in Chicago, that this requirement forces many panels to be replaced which could have been avoided with tandems, a further result of the "union influence" there.

But I may be completely off base...