Original Breaker Panels had Main Fuses not Main breakers heres why

 If you go into an older home or business built in 50s you will more than likely find that the breaker panels that did not have a main breaker and instead had main fuses.

This is because of 2 reasons  1st main breakers where at the time very expensive and main fuses where cheaper . 2nd Main fuses had a higher Fault current rating than main breakers at the time and there was the worry of runaways when a breaker tripped  and main breaker could not handle the amperage produced and damage the electrical system 

In my area you typically find them in the rural   Penelec territory's  in Cambria and Blair County Pa.   as they required main fuses because their systems had higher fault amperage's