two companies involved - there is common ownership between the companies, but they are NOT a controlled group. Each company wants its own plan. Can an owner of both companies participate in both plans, and, does the owner have separate 415 limits in each plan or, since the owners are more than 5% owners, are they constrained by one annual additions limit?

There would be one annual addition limit if the owner was a more than 50% owner or one of the plans was a 403(b).

Sounds like you have two separate limits in your example

BobK

Haven't gone back and double checked, but isn't it just "ratcheted down" from 80% to 50% under 415 in a parent/sub group but remains at 80% for brother/sister?

owners are 25% owners - common interest is 15%. Can they have two annual additions limits?

Sounds like it assuming you have run through all the attribution rules and there is no affiliated service group.

There is no attribution - as for affiliated service group - they don't share clients or resources, they don't exchange services, so I think that means they aren't an ASG. Is that correct?