The overcurrent protection device on the primary side of a transformer operating at less than 1000 volts must be set at no more than __________ percent of the transformer’s rated primary current?

For transformers operating at less than 1000 volts, the overcurrent protection device on the primary side is required to be set at a maximum of 125 percent of the transformer’s rated primary current. This regulation is in place to ensure that the transformer can handle inrush currents and temporary overloads without tripping unnecessarily. The 125 percent setting provides a balance between protecting the transformer from sustained overcurrent conditions while allowing for transient events that may occur during normal operation.

Setting the protection device at this level helps to prevent nuisance tripping and ensures that the transformer has adequate time to manage short-term overloads, which are common during startup or under specific load conditions. It's crucial for maintaining the reliability and longevity of the transformer, as well as for the safety of the electrical system. Understanding this setting is essential for anyone working with transformer installations in compliance with electrical codes and best practices.