Quick Hits

PART VII — SERVICE EQUIPMENT and OVERCURRENT PROTECTION over 1kva

EPISODE 13 — Service Overcurrent Protection — Article 268 FINALE (268.90–268.93)

Slide 1 — Hook "Final episode of Article 268! Wrapping up with overcurrent protection for the service itself."

Slide 2 — 268.90 Where required

• Every ungrounded service conductor needs overload protection — an OCPD in series, rated/set no higher than the conductor's ampacity (single-pole devices on a multipole circuit count as ONE device for this rule).

• Motor-starting currents get to follow 430.52/430.62/430.63 instead; fire pump supply conductors follow 695.5(B)(2)(a).

• The grounded conductor generally can't have an OCPD in it — UNLESS it's a circuit breaker that opens ALL conductors of the circuit simultaneously.

Slide 3 — 268.91, 268.92, 268.93

• 268.91(A): the protective device has to be able to detect AND interrupt any current above its trip/melting point that could occur there. A fuse rated up to 3× conductor ampacity, or a breaker trip setting up to 6× ampacity, satisfies the short-circuit protection requirement.

• 268.91(B): the short-circuit protective device must be integral to (or immediately adjacent to) the service disconnect; if fuses are used, the disconnect has to sit AHEAD of (on the supply side of) those fuses.

• 268.92: if the service OCPDs are locked/sealed/not readily accessible to the occupant, branch-circuit or feeder OCPDs must be added downstream, readily accessible, and rated LOWER than the service OCPD.

• 268.93: to prevent tampering, an automatic OCPD protecting only a specific load's service conductors can be locked/sealed — as long as the lock/seal stays accessible.

Slide 4 — Quiz + CTA Q: "A fuse used for service short-circuit protection is considered adequate if rated up to how many times the conductor's ampacity?" A) 2× B) 3× C) 4× D) 6×

✅ Answer: B — 268.91(A): fuses up to 3× ampacity (breakers up to 6× trip setting) satisfy the requirement.

CTA: 🎉 That's a wrap on ALL of Article 268 — Services Over 1000V! Follow for more daily quick-hit study notes as we continue through the medium-voltage articles.

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