Dakota Welders Guide for Red Seal Guide (CEC 2024)

Types of Welders

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• Transformer Arc and Inverter Welders – Old-school, sturdy, heat-on-demand.
  
• Motor Generator Arc Welders – High-tech and efficient.
  
• Resistance Welders – Zap it and clamp it. Great for precise, controlled joins.
  

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Key Terms You Gotta Know

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• Actual Primary Current: The real current your welder is pulling right now.
  
• Rated Primary Current (RPC): What’s on the welder’s nameplate. It’s your "starting point."
  
• Duty Cycle: How long the welder works before it needs a break.
  
  • Example: 70% = work 7 mins, rest 3 mins.
    

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Receptacles (42-004): What to Know

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• If the welder has a cord, the plug and receptacle can be rated lower than the breaker — but never lower than the RPC.
  
• The receptacle must be labeled with:
  
  • “Welder Use Only”
    
  • Conductor size, material, insulation type, and OC protection rating (80% or 100%)
    

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Transformer & Inverter Welders

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42-006: Conductor Sizing

• You size the conductors by:
  RPC × Duty Cycle Multiplier (Table 42)
  
• Example:
  RPC = 200A, Duty = 70%
  200 × 0.84 = 168A
  Use #1/0 AWG (from Table 2)
  

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42-008: Overcurrent Protection (O/C)

Two rules here:

• Breaker size = up to 200% of the RPC
  
  • 200A × 2 = 400A
    
  • Use Table 13
    
  • GO DOWN to choose 400A
    
• Breaker size based on 200% of wire’s ampacity
  
  • #1/0 AWG = 170A
    
  • 170 × 2 = 340A
    
  • Use Table 13
    
  • GO UP to 350A
    

💡 Use the lower of the two unless one causes frequent tripping.

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Multiple Welders? Time to Group Them!

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42-006 (2) & 42-008 (3)

RW75 Copper

• Welder 1: 100A × 0.89 = 89A → #3awg
  
• Welder 2: 40A × 1.0 = 40A → #8awg
  
• Welder 3: 40A × 0.78 = 31.2A → #10awg
  
• Welder 4: 20A × 0.78 = 15.6A → #14awg
  
• Welder 5: 20A × 1.0 = 20A → #14awg
  

Demand Factor Formula:

• 100% of the 2 biggest
  
• 85% of the 3rd
  
• 70% of the 4th
  
• 60% of the rest
  

Calculation:

• 89A + 40A = 129A
  
• 31.2A × 0.85 = 26.52A
  
• 20A × 0.7 = 14A
  
• 15.6A × 0.6 = 9.36A
  
• Total = 178.88A
  
• Use Table 2: #3/0awg
  

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Over-Current for Grouping

Protecting the Feeder:

• Welder 1: 100A
  
• Welder 2: 40A
  
• Welder 3: 40A
  
• Welder 4: 20A
  
• Welder 5: 20A
  

Calculation:
Pick the Welder with the largest RPC/FLA, use the appropriate multiplier, then ADD the rest. 
(100 × 200%) + 40 + 40 + 20 + 20 = 320A
GO DOWN → 300A

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Resistance Welders (42-014)

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Conductor Sizing

• 70% of RPC for seam/auto welders
  
• 50% of RPC for manual welders
  
• Use Table 42C for exact current & duty cycle
  
• For groups:
  100% of largest + 60% of all others
  

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Overcurrent (42-016)

Resistance welders get more flexibility:

• O/C = Up to 300% of either:
  
  • RPC (GO DOWN)
    
  • Or conductor ampacity (GO UP)
    

Pick whichever gives better protection.

Example:

• 89A × 3 = 267A
  
• Add other welders = 373.8A
  
• GO UP!
  
• Use 400A breaker
  

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Over-Current for Grouping

Protecting the Feeder:

• Pick the biggest RPC
  
• Multiply by 300%, add the rest
  
• GO DOWN

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Disconnects (42-010)

⚠️ If your welder doesn’t come with a built-in disconnect, you must install one.
It needs to be rated high enough to handle the breaker you calculated in 42-008.

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Motor-Generator Arc Welders

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42-012: Conductor Sizing

• RPC × Duty Cycle Multiplier (Table 42B)
  
• Example:
  RPC = 200A, Duty = 70%
  200 × 0.86 = 168A
  Use #1/0 AWG (Table 2)
  

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Grouping

RW75 Copper

• Welder 1: 100A × 0.91 = 91A
  
• Welder 2: 40A × 1.0 = 40A
  
• Welder 3: 40A × 0.81 = 32.4A
  
• Welder 4: 20A × 0.81 = 26.3A
  
• Welder 5: 20A × 1.0 = 20A
  

Demand Factor Formula:

• 100% of the 2 biggest
  
• 85% of the 3rd
  
• 70% of the 4th
  
• 60% of the rest
  

Calculation:

• 91A + 40A = 131A
  
• 31.4A × 0.80 = 25.12A
  
• 26.3A × 0.7 = 18.41A
  
• 20A × 0.6 = 12A
  
• Total = 186.53A
  
• Use Table 2: #3/0awg
  

What About Over-Current Protection?

Rule 42-012 (1) says for Motor-Generator Arc Welders, you use REGULAR MOTOR RULES!!!

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Summary

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• Know your welder type (Transformer-Inverter, Resistance, MG Arc)
  
• Start with the Rated Primary Current
  
• Multiply by Duty Cycle Factor (Table 42A/B/C)
  
• Size:
  
  • Conductors = use Table(s) 1-4
    
  • Breakers = 200% (arc/inverter), 300% (resistance), follow motor rules (MG-Arc)
    
• Use grouping demand factors for multiples
  
• Label your receptacles if they're for welders
  
• Don’t forget your disconnect!

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