RBM wrote:

I don't know the code specific answer to how many amps you can draw
off a main panel, but I can tell you this. In a 4 year old house
here, I just finished helping a friend add a new line for a new
irrigation well. We hooked it to an 80A sub panel that was
installed for the pool eqpt and run off one of the two 150A main
panels. That sub panel had passed local inspection and is more that 50%
of
the main.

Your friend has a 300 amp service split between two "main" panels.
The pool sub panel fused at 80 amps is not greater than half the size
of the main panels. The OP has a 200 amp service, a 100 amp sub
panel, and seems to be asking if he can pull 125 amps on it

I live in what was orginally a duplex. Each side was equipped with 200-Amp
service.

By the simple expedient of adding a door to the common wall, I converted the
building to a single-family residence. Bingo! I have 400-Amp service split
between two main panels.

Is it your position I can now put a 175-Amp sub-panel off of one of the main
panels because such would not exceed 50% of the total power delivered to the
building?