What percentage of the full load current of a transformer is typically used for fuse chart calibration?

The correct percentage of the full load current of a transformer commonly used for fuse chart calibration is 200% to 250%. This range is chosen to ensure that the fuse operates effectively under various fault conditions.

When fuses are calibrated based on the full load current, they need to account for potential overload scenarios. The higher range of 200% to 250% effectively allows the fuse to withstand short-term overloads without blowing immediately. This is crucial for ensuring stability and safety in the network, particularly during moments of inrush current or other transient conditions.

The calibration within this range helps to avoid nuisance tripping while still providing protection against genuine overload situations. In the event of a long-term overload, the fuse will blow within a specific timeframe, protecting both the transformer and the connected loads from damage. This understanding is important in lineman practices, as selecting the right fuse significantly contributes to system reliability and safety.