Quick Hits

Episode 3: Continuity of Power & Locked-Rotor Current Sizing (695.5)

SLIDE 1 / (HOOK / COVER) ⚡ NEC Quick Hit: Continuity of Power & Locked-Rotor Sizing (Part 3) ⚡ 

Why must fire pump overcurrent protective devices be sized to carry locked-rotor current indefinitely? Section 695.5 has strict rules to keep power flowing during a fire. Let's break it down! 👇

SLIDE 2 (DIRECT CONNECTION VS. SINGLE DISCONNECT)

Minimizing Inadvertent Disconnection:

• Direct Connection Preferred: The best way to maintain power continuity is connecting the source directly to the listed fire pump controller without intermediate disconnects.

• Single Disconnect Allowance: If a disconnect and OCPD are installed between the source and controller, they must be limited to a single disconnecting means (except for campus feeders or standby generators).

SLIDE 3 (LOCKED-ROTOR CURRENT & SUPERVISION)

Carrying the Load Indefinitely:

• Sizing for LRC: OCPDs for individual sources must be rated to carry indefinitely the sum of the locked-rotor current (LRC) of the largest fire pump motor plus full-load currents of other pumps and accessories.

• Mandatory Supervision: Disconnecting means must be marked "Fire Pump Disconnecting Means" in 1-inch red letters and supervised in the closed position via central station signal, local alarm, lock, or seal.

SLIDE 4 (WRAP-UP)

💡 Apprentice Pro-Tip: Standard motor OCPDs are designed to thermal-trip during an overload, but a fire pump breaker must never thermal-trip on locked-rotor current. It must hold indefinitely so the pump can fight the fire until destruction!

💬 Save this post for your next fire pump service installation! 🔗 

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