What is meant by inrush current? Does this phenomenon affect every transformer?

When a voltage is applied to a transformer a magnetising current will briefly flow. This ensure that all magnetic particles in the iron core are correctly oriented.

This is referred to as the inrush current. In extreme circumstances this current can amount to 15 or even 20 times the nominal current in the transformer.

At EREA we make a distinction between standard transformers and transformers with a low inrush current.

Inrush current is rarely a problem in an industrial setting. 

In domestic premises, shops and smaller office buildings there is usually insufficient capacity to supply the inrush current for a transformer. The main circuit breaker will often trip when a non-low inrush current transformer is started up.

We have developed our IRC series of transformers for this situation. These can be protected at their nominal current with a type C circuit breaker. This means they can be used in small-scale electrical installations without problems.