To calculate the fuse for a transformer, what multiplier is used?

The correct approach to calculate the fuse for a transformer involves using a multiplier of 1.25 times the total current. This practice is based on industry standards, which incorporate a safety margin to account for potential inrush currents and variations in load conditions. By using this multiplier, the fuse can adequately protect the transformer from overload conditions without being overly sensitive, which could lead to nuisance tripping during normal operation when the transformer experiences temporary increases in current, such as during start-up.

The use of 1.25 times the total current is particularly critical because transformers typically have a higher inrush current that occurs when they are energized. This inrush current can be significantly higher than the normal operating current but only lasts for a short duration. The 1.25 multiplier ensures that the fuse will allow for this brief spike without tripping, thereby maintaining operational efficiency and protecting the integrity of the transformer. This is a widely accepted method in both the National Electrical Code (NEC) and industry practices.

In contrast, the other multipliers proposed may not provide sufficient allowances for the unique characteristics of transformer operation or could lead to premature fuse blowing or inadequate protection in certain scenarios.