Quick Hits

Episode 3: Resistance Welders — Sizing, Multipliers & OCPD (630.31 – 630.34)

SLIDE 1 (HOOK / COVER) ⚡ NEC Quick Hit: Resistance Welders (Part 3 - Article 630) ⚡ 

Spot and seam resistance welders draw massive short-circuit currents to fuse metal. How do you size their supply conductors and overcurrent protection? Let's check out Part III! 👇

SLIDE 2 (RESISTANCE WELDER CONDUCTOR SIZING) Managing High KVA & Low Voltage:

• Individual Welders: Sized at not less than 70% of rated primary current for seam/automatic welders, and 50% for manual nonautomatic welders (or calculated via Table 630.31(A) duty-cycle multipliers).

• Group Sizing: Supply conductors for multiple resistance welders must be at least the largest welder plus 60% of all other welders.

SLIDE 3 (OVERCURRENT PROTECTION & DISCONNECTS) OCPD Capped at 300 Percent:

• Welder OCPD: Each resistance welder must have an OCPD rated or set at not more than 300 percent of the rated primary current of the welder.

• Disconnects: Every resistance welder requires a dedicated switch or circuit breaker sized to match the supply conductor ampacity.

SLIDE 4 (WRAP-UP) 💡 Apprentice Pro-Duty: 

Resistance welders cause significant voltage drop due to their high kVA demand. Sizing conductors to limit voltage drop for proper welder performance often results in wire sizes larger than the minimum thermal ampacity rules require!

💬 Save this post for your next spot welder installation! 🔗 

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