Fuse Speed Explained

The speed of a fuse is essentially the time it takes for the fuse to open when a fault current occurs. The speed at which a fuse opens is governed by the material used in the fuse element, the overload current and the ambient operating temperature.

For example, if a current of 20A was flowing through a fuse rated at 10A, a very fast acting fuse might open in 0.1 seconds, a fast acting fuse may open in one second, whilst a slow acting fuse may take tens of seconds to open.

When replacing a fuse, or choosing a fuse for a new application, it is very important to select a fuse that will open fast enough to protect the circuit from unexpected overloads, but not open under normal operating conditions. The speed of the fuse is also known as the time current characteristic of the fuse.

FUSE SPEED Categories (Element Speed): 

FF: Very Fast Acting (Flink Flink).

F: Fast Acting (Flink).

M: Medium Acting (Mitteltrage). 

T: Slow Acting (Trage or Timed).