Quick Hits

Episode 3: Nameplates, Duct Heaters & Resistance Boilers (425.28 – 425.74)

SLIDE 1 (HOOK / COVER)

⚡ NEC Quick Hit: Duct Heaters & Resistance Boilers (Part 3) ⚡

Permanent nameplates, forced-air duct heater fan interlocks, and boiler overtemperature limits—let's review Sections 425.28 through 425.74! 👇

SLIDE 2 (NAMEPLATES & DUCT HEATERS)

Markings and Airflow Controls:

• Permanent Nameplates: Equipment must feature a permanent nameplate visible after installation showing manufacturer, volts, watts (or amperes), and motor ratings.

• Fan Circuit Interlock: Duct heaters mounted in forced-air systems require a means to ensure the fan circuit is energized when any heater circuit is energized.

• Limit Controls: Duct heaters require an automatic-reset temperature-limiting control plus an independent manual-reset/replaceable supplementary control.

SLIDE 3 (RESISTANCE BOILERS)

Boiler Protection Limits:

• Overtemperature Control: Boilers operating without a state change in the heat transfer medium require a temperature-sensitive limiting means to disconnect ungrounded conductors.

• Overpressure Control: Boilers with a liquid-to-vapor state change require a pressure-sensitive limiting means to disconnect ungrounded conductors.

SLIDE 4 (WRAP-UP)

💡 Apprentice Pro-Tip: Always verify that industrial process duct heaters have an active fan interlock wired in—firing up heating elements without proper airflow will instantly trip thermal limits or melt ductwork!

💬 Save this post for your next mechanical and HVAC integration project!

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← Article 425: Fixed Resistance and Electrode Industrial Process Heating Equipment

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