Is it permissible to use a 600-volt AC rated fuse on a 300-volt DC application?

Using a 600-volt AC rated fuse on a 300-volt DC application is permissible according to the half voltage rule, which allows for the use of AC-rated devices in DC applications under certain conditions. The half voltage rule states that when an AC component is rated significantly higher than the DC voltage, it can be used safely because AC rated devices typically handle surge currents and thermal issues differently than those designed specifically for DC.

However, it is important to note that while the fuse might be rated for a higher voltage, it is essential to consider other factors related to its characteristics when used in a DC circuit, such as current interruption capability which can vary between AC and DC due to the nature of the voltage and current flow. Therefore, while a higher-rated fuse can typically be used, ensuring it is marked for DC use adds an extra layer of safety and compliance with electrical standards.