Did one leg of our 1950's 100 amp main breaker fry because it was overloaded by too many dedicated circuits?

We have a main breaker with two "legs" outside our house and our main panel inside. Last week, an electrician installed 4 new dedicated circuits -- one each for microwave, kitchen lights, and 2 bathrooms. Yesterday, one "leg" of the main breaker fried turning off all the electricity to the kitchen (except the fridge thankfully!) and 2 baths. Today, since one "leg" still works, he did a temp fix and wired everything to that one leg so at least we've got lights in the kitchen and bathrooms. The kitchen lights are buzzing though...

So, is it just coincidence that everything was working fine until he put in the 4 dedicated circuits? He ONLY worked on the kitchen and 2 bathrooms and it was ONLY the kitchen and 2 bathrooms that were without electricity. He didn’t work on the fridge outlet though and that was the only outlet still working when the others went out. I’m kind of wondering why he put all 4 on that one "leg." Did he overload it? Did he do something else that he’s not being upfront about? Or is it really just coincidence?

Any suggestions on what to do next? Please help me troubleshoot.

Thanks!
Monica

This is hard to say. All to often, something old that was working fine, blows up after any disturbance. The refrigerator kept working because it was on the other leg, just a coincidence. If you did not add to the load, just spread it out among more breakers, it shouldn't have over loaded the breaker. He may have put all the new circuits on the same leg because that was where there was space for the breakers, or because he studied the loads, and decided the other leg was loaded heavier, and it would be better to put them on that one.

If you have the whole house on the one leg now, and haven't blown up that leg, it shouldn't have blown up the other one to carry part of the load. A new breaker with the loads properly distributed might be a good solution. I don't like the buzzing lights. Do something soon.

If not, you may be talking a new 200 amp box to keep up to modern loads.