The 200 amp SQ-D panel I'm working with in a home is full. I need to add about 5-120v circuits and 2-240v out to a new attached garage. I could pull the singles and add twins but some inspectors don't like a lot of twin breakers. I will add a 100 amp sub-panel in the garage feeding it with a 100a breaker (which I'll have to add 4 twins to make room) but think this will be better. Also, will adding the 100a panel be a problem with loading the 200a panel? Thanks for any input.
The Golden Rule - "The man with the gold makes the rule"
Just because they make tandem breakers that fit doesn't mean you should use them. One sure way to tell is if there will be more than 42 (40 in most) poles/breakers, then the panel is not meant to have tandems. You may have a 30/40 panel that can have 10 tandems, but it sounds like you may run over that. You may need to add the sub panel in the garage and another sub next to the main panel.
I have argued on this board that the 42 circuit limit is ridiculous and 1 or 2 tandems should be allowed, but you sound like you need a lot more than 1 or 2. Also, it may be a code violation, depending on your panel.
#40429 - 07/20/0409:16 AMRe: Twin breakers or Sub-panel?
Not only is there the 42 NEC limit, but each panel has a limit. Look at the fine print inside the can. If your 200 amp panel already has 42 full spaces, then your other alternative is to do a load study of each branch circuit, and combine those that you can.
#40430 - 07/20/0411:05 AMRe: Twin breakers or Sub-panel?
The subpanel next to the main panel is for the circuits that are displaced for the feeder connections. If the main panel is full, you need to move four poles to the subpanel, freeing four poles in the main panel. Then, two of those poles feed the new subpanel, and the other two feed the remote subpanel with all the new circuits.
You can, of course, also put some of the new circuits on the subpanel next to the main panel.
#40432 - 07/20/0402:53 PMRe: Twin breakers or Sub-panel?