Quick Hits

Episode 20 — Supervised Industrial Installations

Covers: 240.90, 240.91, 240.92

Hook: Last episode of Article 240 — a special part just for qualified-personnel-supervised industrial facilities, with its own math.

Slide 2: Part VIII only applies to the manufacturing/process-control portions of a supervised industrial installation, and everything else in Article 240 still applies unless specifically modified here. For OCPDs rated over 800A, conductor ampacity must be at least 95% of the OCPD rating (instead of matching it outright) — but only if the conductors are protected within recognized short-circuit time/current limits and all terminating equipment is listed and marked for that application.

Slide 3: Location rules largely mirror 240.21, but feeder taps under the 25-ft rules can be sized using the short-circuit current-rating formulas in Table 240.92(B) instead. Separately derived transformer secondaries get their own tap allowances (short-circuit/ground-fault protection via limited length + primary OCPD sizing, differential relaying, or engineering calculations; overload protection via single/grouped OCPDs or relaying; plus physical protection). Outside feeder taps follow the same unlimited-length logic as the general outdoor tap rules, and primary-side protection can cover the secondary where the time-current characteristics, adjusted by the voltage ratio, effectively protect it.

Quiz: In a supervised industrial installation, what percentage of an over-800A OCPD's rating must the conductor ampacity meet?
Answer: At least 95%.

CTA: That wraps Article 240! Follow for Article 250 — Grounding and Bonding — next up in the Chapter 2 series.

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