Selection of power electronics fuses

This page gives guidance on how to select the appropriate type of fuses for the protection of power electronics equipment. Some information is given on European and US requirements.

Which fuse for which job?

Basically fusing will be used to protect either the circuit supplying power to the equipment, or to protect the equipment itself. For the supply circuit, this is commonly referred to as 'branch circuit protection' or BCP. BCP need not be a fuse - instead it could be provided by a circuit breaker, depending on customer preference and other considerations. 

 Branch circuit protection:

Fuses used for BCP tend to be relatively 'slow' fuses. This means that they are not very sensitive to rapid changes in current going through them such as would be seen during a short circuit. They are designed to adequately protect against short circuits but they are also required to provide overload protection  - which is protection of the circuit over a typically longer time period.


Equipment fusing:

Equipment or product fuses are designed and selected by the user to protect the equipment in service against damage and to prevent the equipment becoming unsafe during a fault condition. This fuse will often be fitted in the equipment but it is also perfectly normal for it to be fitted outside of the equipment. It justs depends on the design approach taken by the equipment manufacturer. There are pros and cons for each approach.

By using an equipment fuse, it is possible to provide coordinated protection that will protect the system against damage and isolate it from the electrical supply so that no other equipment or systems in the vicinity are affected by the fuse in question blowing.