Dakota Motor Bank Feeder Guide for Red Seal Exam (CEC 2024)

You have a group of motors (a motor bank) that are all connected to a single feeder conductor — and you need to size that conductor correctly so it doesn’t overheat or trip the system when the motors run.

This follows CEC Rule 28-108 which gives us a method to size the feeder conductor based on the types of motor duty (continuous, short-time, or intermittent).

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Example

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Step 1: Handle Continuous Duty Motors

According to Rule 28-108(1)(a):

Take the largest continuous duty motor, multiply its FLA by 125%, then add the FLA of any other continuous duty motors.

• Largest continuous: 40A
• Multiply: 40 × 1.25 = 50A
• Add other continuous: +36A
  → Total for continuous motors = 86A

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Step 2: Handle Short-Time and Intermittent Motors

Use multipliers from Table 27:

• Short-Time (STD) 5 min = 110% → 50 × 1.1 = 55A
• Intermittent (ID) 15 min = 85% → 60 × 0.85 = 51A

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Step 3: Add Them All Together

Now add all the calculated values:

• Continuous motors: 86A
• Short-Time motor: 55A
• Intermittent motor: 51A

Total= 86 + 55 + 51 = 192A

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Step 4: Choose the Right Conductor Size

Use CEC Table 2, 75°C column:

• You’re looking for a conductor with at least 192A ampacity
• From Table 2 → 3/0 AWG copper is rated 200A at 75°C

Answer: 3/0 AWG copper is your minimum feeder conductor size

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Super Fun Fact!

Since this feeder conductor doesn’t directly touch any motors, Rule 4-006 (conductor correction/derating) may apply depending on your installation (e.g., ambient temp, bundling, etc.).