The answer to 'when to replace fuse box' is that it's generally recommended to replace an older fuse box every 40-60 years, or sooner if it's showing signs of wear or damage. Older fuse boxes may become less reliable and pose fire hazards as the components degrade over time. Upgrading to a modern circuit breaker panel can also improve safety and increase your home's electrical capacity to handle more power-hungry appliances and devices.
It's important to have a licensed electrician inspect your fuse box and determine if replacement is necessary. They can evaluate the condition of the components, check for any code violations or safety issues, and recommend the best course of action for your home.