Secondary current
The current delivered to the load connected to the secondary (I2).
Definition
The secondary current is the current delivered by the transformer to the load connected to its secondary winding. It is denoted I2 and is the sizing quantity for the cables, protections and equipment supplied downstream.
The relationship between primary and secondary current is inverse to the turns ratio: if U2 < U1 (step-down transformer), then I2 > I1. A 400 V/24 V transformer drawing 1 A on the primary delivers about 16 A on the secondary (losses aside). This is why low-voltage secondary terminals are always sized for larger cable cross-sections.
Under a secondary short circuit, the current can reach very high values, limited mainly by the short-circuit impedance of the transformer. It is this characteristic that determines the breaking capacity of the downstream protections.
The ABL tip
For installations with many secondary outgoing circuits, ABL Transfo can integrate a low-voltage distribution board directly into the transformer enclosure. This simplifies wiring and ensures optimal discrimination between the protections.
