CEC Rule 28-106

Conductor Size for Individual Motors

Canadian Electrical CodeCEC 2024NEC Equivalent: NEC 430.22

Motors run hot, and continuous-duty motors can run for hours or days without stopping. To prevent the wires feeding them from severely overheating, the Canadian Electrical Code mandates a safety multiplier. You must calculate 125% of the motor's Full-Load Current (FLC). Crucially, per Rule 28-100, you obtain this FLC value from Table 44 (for three-phase) or Table 42 (for single-phase)—NOT the motor nameplate! You multiply that Table FLC by 1.25, and then you use CEC Table 2 to select a wire that can safely carry that adjusted current. It is mathematically identical to the NEC's 430.22 rule and is the very first step in sizing any motor circuit.

When You Need This

  • Sizing conductors for new rooftop HVAC units, pumps, or industrial machinery.
  • Confirming wire size during motor replacement.
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Key Points

1Branch-circuit conductors for a single motor must be sized at 125% of the motor FLC.
2The motor FLC MUST come from CEC Table 42 or Table 44, not the nameplate.
3If the motor is non-continuous duty, Table 27 provides different percentage multipliers.
4For multiple motors on a single feeder (Rule 28-108), you take 125% of the largest motor FLC plus 100% of the remaining motors.

Common Mistakes

Using the motor nameplate FLA instead of Table 44 to calculate the 125% requirement.

Forgetting to apply the 1.25 multiplier entirely.

Applying the 125% rule to the overload protection (overloads use the nameplate FLA, not the table FLC).

Exam Tip

Red Seal exams frequently test Rule 28. Always grab the FLC from Table 44, multiply by 1.25, and select the wire from Table 2. Remember that the CEC demands the Table FLC for wire and breakers, but Nameplate FLA for Overloads (Rule 28-306).

Frequently Asked Questions

You do not use the 125% multiplier for short-time duty motors. Instead, you refer to CEC Table 27 which will give you a specific multiplier based on the duty cycle and time rating.

Inline Tools

Motor FLC Calculator

Look up full-load current for any motor HP and voltage

Related Code Sections

CEC Table 2Ampacity of Insulated Conductors

This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.