I have a new 20 Amp Afci breaker powering 7 outlets in a bedroom. (Unfinished basment). When I use my mitter saw, the breaker keeps tripping. When the saw is plugged into the exsisting 15amp gfci outlet, it works fine

Forgot to mention afci breaker is connected correctly. Return from outlets( white) is going to return/white terminal on the breaker. The white pigtail on the breaker is connected to the neutral bus in the panel. All grounds are connected.

I suspect your miter saw motor uses brushes, which arcing produced at the brushes will be seen by the Arc Fault device as a problem.

Do other things work in that outlet?

Other devices work OK on this circuit. Shop vac, elec drills, etc. I'll just have to use a different circuit to plug my saw into. Thanks for the replies..

These other itmes have motors that use brushes also, and make arcs.

The AFCI breaker may be trying to tell you something is wrong with the miter saw.

Or it may just not like it.