Quick Hits

Episode 2: Power Sources, OCPD Ratings & Sizing (724.40 – 724.45)

SLIDE 1 (HOOK / COVER) ⚡ NEC Quick Hit: Class 1 Power Sources & OCPD Rules (Part 2) ⚡ 

How do you size overcurrent protection for 18 AWG and 16 AWG Class 1 conductors? Section 724.40 sets strict limits on transformers and power sources. Let's look at the math! 👇

SLIDE 2 (CLASS 1 OCPD RESTRICTIONS)

Protecting Small Conductors:

• Strict Ampacity Limits: Overcurrent protection shall not exceed 7 amperes for 18 AWG copper and 10 amperes for 16 AWG copper conductors.

• Non-Interchangeable: OCPDs protecting alternative Class 1 power sources cannot be interchangeable with devices of higher ratings.

SLIDE 3 (OCPD LOCATION RULES)

Where Do Fuses and Breakers Go?

• Point of Supply: OCPDs must be located at the exact point where the protected conductor receives its supply.

• Transformer Primaries: Secondary conductors supplied by a single-phase 2-wire transformer can be protected on the primary side if sized correctly using the transformer voltage ratio.

SLIDE 4 (WRAP-UP)

💡 Apprentice Pro-Tip: Don't confuse Class 1 conductor ampacity rules with standard building wire! Because 18 AWG and 16 AWG are permitted under Class 1, their OCPD limits are hard-capped at 7A and 10A regardless of typical insulation ampacity tables.

💬 Save this post for your next control panel sizing calculation! 🔗 

More code breakdowns at www.JoshTheSparky.com

← View Chapter 7 Home

← Back To Article 724 Home

← Back To Quick Hits Home