Circuit breaker derating refers to adjusting the installed circuit breaker's rated current to match the actual electrical system requirements by replacing fuses or modifying parameters. This ensures safe equipment operation when the original rated current exceeds the real-world load. The primary reason for derating is that when electrical equipment operates below its rated current, an oversized circuit breaker may fail to provide proper protection, leading to operational risks or unexpected power interruptions. So, have you considered these factors when selecting a circuit breaker? Why is derating necessary? When is it required? How much derating is appropriate? Let's explore below.

※ Why Derate a Circuit Breaker?

First, derating is required when the operating ambient temperature exceeds specified limits. Standard thresholds are 40°C (or 65°C for motor protection applications).

※ When Is Derating Necessary?

1. Outdoor installation in high summer temperatures (ambient temperature >40°C).

2. Indoor installations with poor ventilation, where internal cabinet temperatures exceed 40°C even if room temperature is lower.

3. Air-conditioned rooms with densely packed circuit breakers and inadequate heat dissipation.

※ How Much Derating Is Needed?

Derating depends on installation conditions and load rates, but exact values vary. Typically:

· Use a derating factor of 0.8 for high ambient temperatures or poor heat dissipation.

· Apply 0.7 in extreme cases.
Over-derating increases cable costs and reduces short-circuit protection sensitivity. Avoid excessive derating.