CEC Rule 14-104

Rating of Overcurrent Devices

Canadian Electrical CodeCEC 2024NEC Equivalent: NEC 240.4

This is Canada's equivalent to NEC 240.4. The core principle is simple: the overcurrent device (OCPD) is there to protect the wire from melting. Therefore, the rating of the trip element or fuse cannot be higher than the steady-state ampacity of the conductor. However, 14-104(a) provides the 'next standard size' exception: if the conductor's ampacity does not correspond to a standard OCPD size (which are listed in Table 13), you are permitted to use the next higher standard size, provided the rating does not exceed 800A. Additionally, Rule 14-104(2) places absolute hard caps on small conductors: 15A max for #14 AWG copper, 20A max for #12 AWG copper, and 30A max for #10 AWG copper. Unlike some other rules, these max breaker sizes are locked in stone for general-purpose circuits.

When You Need This

  • Choosing the right circuit breaker for standard residential branch circuits.
  • Rounding up to the next standard breaker size for feeders.
  • Sizing protection for derated wires where the new ampacity is non-standard.
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Key Points

1The overcurrent device cannot exceed the conductor's tabulated ampacity (after derating).
2If the ampacity falls between standard sizes (Table 13), you may round up with a maximum of 800A.
3Above 800A, you must round down.
4#14 AWG is capped at a 15A breaker.
5#12 AWG is capped at a 20A breaker.
6#10 AWG is capped at a 30A breaker.

Common Mistakes

Trying to put a 20A breaker on #14 AWG wire because its 90°C rating is higher than 15A (capped at 15A).

Rounding up to the next standard size on a service over 800A (you must round down).

Confusing overload protection limits with short-circuit rules for motors.

Exam Tip

Always verify Table 13 standard sizes before assuming a breaker size exists. Memorize the small conductor limits: 14=15A, 12=20A, 10=30A.

Frequently Asked Questions

Yes, but only in specific scenarios like motor circuits (Rule 28) or A/C equipment where the OCPD acts only as short-circuit protection, not overload protection.

Inline Tools

Circuit Breaker Calculator

Find the correct OCPD size for your circuit

Related Code Sections

CEC Table 2Ampacity of Insulated Conductors

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