I visited a multiple dwelling house today that had two service panels and two meters connected on the same mains entrance. Each dwelling is wired as such:
Bus (common) → Meter → Fused switch → Conduit to dwelling → Breaker panel
The fused switch is connected to the meter via a short length of EMT conduit, providing ground to the switch box. The circuit that leads to the breaker panel is just armored cable (BX) without dedicated ground.
The breaker panel is your typical Square D QO Loadcentre with a 100A main breaker. The fused switch, however, is rated 60A with two 60A fuses in it and a neutral lug. The meter box has markings for 120V/240V 60A. I understand that the purpose of the 60A fuse is to protect the meter and possibly the circuit that feeds the breaker panel.
Is it normal to have a 100A main breaker installed in a panel that is fed from a circuit with a 60A fuse? If not, should the main breaker be replaced with a 60A breaker?
If the breaker panel had a 60A main breaker, would having the fuse be a requirement? i.e. could the switch be replaced with a non-fused, 60A switch?
Is it possible that the circuit leading to the breaker panel is rated for 100A (plus safety margin), but the 60A fuses have been installed only to protect the power meter rated at 60A?