CEC Rule 4-006
Temperature Limitations at Terminations
Just like NEC 110.14(C), the Canadian Electrical Code (Rule 4-006) ensures that a hot wire doesn't melt a sensitive breaker or lug. Even if you run 90°C-rated wire (like RW90), you cannot safely push 90°C worth of current through it if the breaker it connects to is only rated for 75°C. Rule 4-006 dictates that for equipment rated 100A or less (or marked for use with #1 AWG or smaller), you must assume a 60°C termination rating unless marked otherwise. For equipment over 100A (or marked for conductors larger than #1 AWG), you assume a 75°C rating. The great benefit here is that you can still use the 90°C column from Table 2 as your starting point for derating (due to ambient temperature or grouping), as long as your final loaded ampacity does not exceed the limit set by the termination rating.
When You Need This
- Selecting wire sizes for panels where breakers have strict thermal limits.
- Calculating derating factors for hot environments while ensuring the termination won't overheat.
- Passing a Canadian electrical inspection regarding conductor sizing.
Key Points
Common Mistakes
Using the 90°C ampacity from Table 2 as the final value when the breaker is only rated for 75°C.
Assuming all residential equipment is 75°C rated—many small devices are strictly 60°C.
Failing to derate from the 90°C column when using RW90 wire, leaving ampacity on the table.
Exam Tip
For the Red Seal, remember the 100A / #1 AWG threshold. If it's 100A or less, it's 60°C unless marked otherwise. If it's over 100A, it's 75°C. Always use the 90°C column for derating but capping at the terminal rating.
Frequently Asked Questions
Only if every single component in the circuit (the breaker, the lugs, the device) is explicitly rated and marked for 90°C, which is rare in standard commercial/residential equipment.
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Related Code Sections
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.