Every tenant needs to have access to his 50 amp breaker.
Your main disonnect would usually be immediately after the meter, and before the trough- assuming that the apartments are not individually metered.
A more common install would have the service conductors exit the riser directly into the trough. In the trough, the service would be split to a meter for each address- with a disconnect just after each of those meters.
You are allowed to use this arrangement- one without a "main" disconnect- where there are no more than six meters.
I really think you need to talk to both your town hall, and your power company. It sounds as if this was a rather half-baked conversion, and there may be other issues you will need to address as well.
