How to combine fuses with overload relays?

How to combine fuses with overload relays?


Fuses prevent short circuits from damaging the
installation and in worst case causing a fire, and must
therefore have adequate capacities. The lower currents
are cleared by the overload relay. Here, the rated
current of the fuse does not correspond to the motor
rating but to the current, which is likely to damage the
weakest components in the installation. As mentioned
previously, the fuse provides short circuit protection
and does not provide low overcurrent protection.


The illustration on your right-hand side shows the
most important parameters that form the basis for a
successful co-ordination of fuses and overload relays.
It is essential that the fuse trips out before thermal
damage of other parts of the installation occur because
of short-circuit

The most important parameters that form the basis for a successful co-ordination of fuses and overload relays.

The fuse time current curve always has to be situated lower
than the limit curve (red curve) for thermal damage.