I own a duplex with two older electric fuse panels. The tenants have been replacing small fuses with bigger fuses and I am concerned that this could be a problem. Is there any way I can control this situation?

 You are absolutely right that this is a problem that you should control. Over-fusing a branch circuit can lead to an electrical fire. Unfortunately, it is hard to educate every person living in your building about using the correct fuse for the branch wire size. However, you can purchase fuse rejecter washers that will restrict the size of the fuse that fits in the corresponding fuse holder. In other words, with a fuse rejecter screwed into the fuse socket no one can install a larger fuse than required in that opening. There are also “Type S” fuses available designed to prevent the wrong fuse from being introduced as circuit protection.

 When purchasing fuses, look for type “Type P” fuses. They are designed to sense high temperatures around the fuse and blow even though the current draw is low. Appliances with large electric motors like refrigerators and freezers should be fused with “Type D” fuses that permit extra current to flow on a demand start-up without “nuisance” blowing the fuse. This will help limit the number of times your tenants need to replace fuses. Fortunately, for the safety of you and your tenants most modern fuses are designated “Type D and Type P”.