Quick Hits

Episode 17 — Cartridge Fuses and Reducing Arc Energy

Covers: 240.60, 240.61, 240.67

Hook: Bigger fuses need bigger rules — cartridge fuses, plus a serious safety requirement for large ones: arc energy reduction.

Slide 2: 300-volt cartridge fuses/fuseholders work on circuits ≤300V between conductors, or single-phase line-to-neutral circuits off a solidly grounded 3-phase 4-wire source at ≤300V to neutral. Fuseholders are designed to resist accepting the wrong class of fuse, and current-limiting fuseholders reject non-current-limiting fuses. Fuses need to be marked with ampere rating, voltage rating, interrupting rating (if other than 10,000A), current-limiting status if applicable, and manufacturer info. Class H renewable cartridge fuses are replacement-only, same logic as Edison-base plugs.

Slide 3: Fuses rated 1200A or higher trigger arc energy reduction requirements — documentation on fuse location and the method chosen has to be available, and either the fuse clears in 0.07 seconds or less at available arcing current, or one of several reduction methods (differential relaying, energy-reducing maintenance switching, active arc-flash mitigation, current-limiting electronically-actuated fuses, or an approved equivalent) has to be set below the available arcing current. The system gets performance-tested on-site when first installed, with written records kept.

Quiz: At what fuse rating does the arc energy reduction requirement kick in?
Answer: 1200 amperes or higher.

CTA: Follow — Part VII, circuit breakers, starts next.

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