To me it looks like he's got 100A for the whole house, 40A breaker for the garage and 80A for the rest of the house.  Wouldn't that allow up to 40A (at 230v = 9,200Watts) in the garage (if at full load, that would leave 60A for the rest of the house) or 80A for the rest of the house (leaving 20A for the garage).  If it goes over 100A for both then shouldn't the main 100A breaker flip?  So he should be able to use up to 40A in the garage, as long as his rest of the house load isn't over 60A?  If it goes over, shouldn't the main 100A breaker flip and then no the house wouldn't theoretically burn down?  (wh00per, that's a question mark there just in case you're not sure I'm asking a question).