[jhudson12]

I have 30 women with sewing machines in the same room. They all are using basically the same amps... 12 amps. How many breakers do I need and of what ratings?

[donf]

OK, J Hudson

Lets think about this, each breaker can handle up to 20 Amps. Each line uses a 12 Amp Sewing Machine. 12 from 20 =8 Amps. On raw math alone, you can put one sewing machine on one circuit, safely.

[Yipster]

Treating each sewing machine as a motor load, and making an assumption that this is an industrial setting, your sewing machines would be considered continuous loads. This brings the loads ampacity to 15A (125% of the motors load), so like donf states, the load is one sewing machine per breaker, with no additional load exceeding 5A being placed on that same breaker.

[labman]

12 amps each? Are these large, industrial machines?

[Stratmando]

I would use 30 20 amp breakers. Lighting on separate circuit(s).