Which of the following is not considered the protecting overcurrent protective device for a panelboard directly fed from the secondary conductors of a transformer?

Which of the following is not considered the protecting overcurrent protective device for a panelboard directly fed from the secondary conductors of a transformer?

• A. The secondary OCPD on the transformer
• B. The main OCPD inside the panelboard
• C. The primary OCPD on the feeder supplying the transformer
• D. The branch-circuit OPD protecting a downstream load

Answer: (C)

When a panelboard is fed from the secondary of a transformer, the protection for the panelboard comes from devices on the transformer's secondary side and from the panelboard itself. The protecting device on the transformer's secondary side trips to guard against overloads on that side, and the main disconnect inside the panelboard protects the panelboard and its downstream circuits. A branch-circuit OCPD protects a downstream load, not the panelboard itself, though it is part of the panelboard’s protection scheme. The device on the feeder that supplies the transformer—the primary OCPD on that feeder—lies on the transformer’s primary side and protects the transformer’s supply circuit, not the panelboard’s secondary side. Therefore, that primary OCPD is not considered a protecting device for the panelboard fed from the transformer's secondary.

When a panelboard is fed from the secondary of a transformer, the protection for the panelboard comes from devices on the transformer's secondary side and from the panelboard itself. The protecting device on the transformer's secondary side trips to guard against overloads on that side, and the main disconnect inside the panelboard protects the panelboard and its downstream circuits. A branch-circuit OCPD protects a downstream load, not the panelboard itself, though it is part of the panelboard’s protection scheme. The device on the feeder that supplies the transformer—the primary OCPD on that feeder—lies on the transformer’s primary side and protects the transformer’s supply circuit, not the panelboard’s secondary side. Therefore, that primary OCPD is not considered a protecting device for the panelboard fed from the transformer's secondary.