For interconnected sources, the feeder ampacity must be at least what percent of the power source output current?

For interconnected sources, the feeder ampacity must be at least what percent of the power source output current?

• A. 25%
• B. 100%
• C. 125%
• D. 175%

Answer: (C)

When multiple power sources can feed the same circuit, the conductors feeding that bus must have extra capacity, not just the exact output of one source. The rule requires sizing the feeder ampacity at least 125% of the power source output current. The 125% margin provides room for backfeed interactions between sources, peak/continuous loading, and safe operation without overheating or nuisance tripping. For example, if a source can supply 80 A, the feeder must be rated for at least 100 A (80 × 1.25). The other percentages would not give enough margin (25%), would give no headroom (100%), or exceed what the standard requires (175%).

When multiple power sources can feed the same circuit, the conductors feeding that bus must have extra capacity, not just the exact output of one source. The rule requires sizing the feeder ampacity at least 125% of the power source output current. The 125% margin provides room for backfeed interactions between sources, peak/continuous loading, and safe operation without overheating or nuisance tripping.

For example, if a source can supply 80 A, the feeder must be rated for at least 100 A (80 × 1.25). The other percentages would not give enough margin (25%), would give no headroom (100%), or exceed what the standard requires (175%).