Quick Hits

Episode 2: Supply Conductors, SCCR & Flexible Cords (646.7 – 646.10)

SLIDE 1 (HOOK / COVER) ⚡ NEC Quick Hit: MDC Conductors & Flexible Cords (Part 2) ⚡ 

How do you size supply conductors for a modular data center? Can you run flexible power cords from an external service into an MDC? Let's check out Section 646.7! 👇

SLIDE 2 (125% CONDUCTOR SIZING & SCCR)

Continuous Load Calculations:

• 125% Rule: Because an MDC is treated as a continuous load, supply conductors must have an ampacity of not less than 125 percent of the full-load current rating.

• Short-Circuit Ratings: Service equipment connected directly to a service must have an SCCR not less than the available fault current of the service.

SLIDE 3 (STRICT RULES ON FLEXIBLE POWER CORDS)

Internal vs. External Cord Limits:

• Internal Connections Permitted: Flexible power cords (extra-hard usage, wet-rated/sunlight-resistant if outdoors) are permitted only for connections between internal MDC equipment enclosures (such as between a server rack and a power distribution unit).

• External Ban: Flexible power cords shall not be used to connect an MDC to external sources of power like electrical services, feeders, or premises branch circuits!

SLIDE 4 (WRAP-UP)

💡 Apprentice Pro-Tip: You can use flexible power cords inside an MDC to link modular server pods together, but your main incoming feeder must always be wired using a permanent Chapter 3 wiring method. No temporary drop cords from external services!

💬 Save this post for your next MDC installation checklist! 🔗 

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