FUSING OF TRANSFORMERS

Short circuit protection for a transformer is connected on the primary side and must have slow characteristics due to high inrush currents in the transformer. Ideally this should be a motor protection adjusted at the theoretical short circuit current for the transformer and therefore have a higher value than the overload protection. The short circuit calculation we have done in table is for an ideal short circuit close to or inside the transformer.

The short circuit protection is not an overload protection. 

Overload protection is placed on the secondary side close to the transformers connectors and must be maximum the transformers current on the marking plate and with a characteristic depending on the type of load: Electronics needs to be disconnected immediately, contactors have high inrush currents. See also our contactor test.