Which statement about sizing the feeder OCPD is correct?

Which statement about sizing the feeder OCPD is correct?

• A. The OCPD must protect only branch circuits
• B. The OCPD must be sized to at least the calculated load after demand factors
• C. The OCPD is optional
• D. The OCPD should be the smallest device that will fit

Answer: (B)

Sizing the feeder OCPD is all about matching protection to the actual load the feeder will carry. You determine the feeder’s expected current by calculating the connected load and then applying demand factors, which account for the fact that not every circuit draws maximum current at the same time. The protective device on the feeder must be rated at least as high as that calculated load so the feeder can handle normal operation without nuisance trips, but it must not be undersized relative to the conductor’s capacity. This ensures the feeder conductors are protected from overload. That’s why the correct approach is to size the OCPD to the calculated load after applying demand factors. It’s not optional, and it’s not about using the smallest device that fits or protecting only branch circuits.

Sizing the feeder OCPD is all about matching protection to the actual load the feeder will carry. You determine the feeder’s expected current by calculating the connected load and then applying demand factors, which account for the fact that not every circuit draws maximum current at the same time. The protective device on the feeder must be rated at least as high as that calculated load so the feeder can handle normal operation without nuisance trips, but it must not be undersized relative to the conductor’s capacity. This ensures the feeder conductors are protected from overload.

That’s why the correct approach is to size the OCPD to the calculated load after applying demand factors. It’s not optional, and it’s not about using the smallest device that fits or protecting only branch circuits.