Where must the overcurrent protection be located if a panelboard is supplied through a transformer?

The correct placement for overcurrent protection when a panelboard is supplied through a transformer is on the secondary side of the transformer. This is crucial because the transformer steps down or steps up voltage levels, and the overcurrent protection must be sized and located where it can adequately protect the load served by the panelboard.

By placing the protection on the secondary side, it ensures that any fault occurring downstream of the transformer is detected and mitigated. This allows for appropriate circuit protection to handle the specific characteristics of the electrical load connected to the panelboard, considering factors like current rating and fault conditions that the transformer has to support. Properly located overcurrent protection assists in preventing potential damage caused by overloads or short circuits after the transformation process.

While other locations such as the primary side or other points may logically seem relevant, they do not cater directly to the protection needs of the secondary system where the actual distribution to the loads occurs. Therefore, ensuring that overcurrent protection is correctly positioned on the secondary side is essential for the safety and reliability of the electrical system.