Quick Hits

Episode 4: Duct Heaters, Resistance Boilers & Low-Voltage Heating (424.57 – 424.104)

SLIDE 1 (HOOK / COVER)

⚡ NEC Quick Hit: Duct Heaters & Boilers (Part 4) ⚡

Forced-air duct heater fan interlocks, boiler overtemperature limits, and low-voltage heating rules—let's finish Article 424! 👇

SLIDE 2 (DUCT HEATERS & BOILERS)

Airflows and Thermal Limits:

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

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

• Boiler Limits: Resistance-type and electrode boilers must be equipped with temperature-sensitive (or pressure-sensitive) overtemperature limit controls that disconnect all ungrounded conductors.

SLIDE 3 (LOW-VOLTAGE FIXED SPACE HEATING)

Low-Voltage System Limits:

• Power Unit Caps: Low-voltage fixed electric space heating must use an isolating power unit with an output not exceeding 25 amperes, 30 volts AC (42.4V peak), or 60 volts DC.

• Grounding & Protection: Secondary circuits shall not be grounded, and ground-fault protection is not required for low-voltage systems.

SLIDE 4 (WRAP-UP)

💡 Apprentice Pro-Tip: 

Always verify that duct heaters have an active fan circuit interlock—energizing electric heating elements without airflow will instantly trip thermal limits or cause a fire!

💬 Save this post for your final code review on Fixed Electric Space-Heating Equipment!

🔗 More code breakdowns and study tools at www.JoshTheSparky.com

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