Welcome. My name is ***** ***** would be glad to assist.
It sounds like, you have a 200 amp main service from a single utility meter, is this correct?
Then you have connected an apartment to this main? What amperage 100?
How is this connection taking place? Is the main a breaker panel?
Does the panels identification label show that a 100 amp breaker can be used in the panel?
Or is this some other type of disconnect?
The total allowed connection on any single service must be calculated and determined as suitable, so need all the electrical appliances, along with all
the sqft area of both apt and house to begin any type of determination of the load.
Let me know and we can continue,