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MCCB operating temperature range.

The generally accepted standard ambient operating temperature range for Eaton molded case circuit breakers is -20°C to +70°C.

The low end of the acceptable range is dictated as a physical constraint of mechanical operation, and revolves heavily around appropriate substances used in lubricating moving parts (for the given operating temperature range). Circuit breaker operation at low temperatures is not a current sensing accuracy issue. For example different lubricants are used for freeze tested MCCBs (operation to -57°C), but the componentry used in building/assembling the breaker is the same for a freeze tested breaker as for a standard breaker.

As a side note we also can say that if the conducting medium for the breaker (connected wiring) is the same temperature as the breaker itself, then the standard time current curve for the breaker applies even when the breaker is operated at low temperatures.

There sometimes is not a lot of published official documentation on subjects such as “circuit breaker general operating temperature range” because these type devices are generic in nature. Any operating temperature requirements or restrictions are more likely to be assembly-related, such as published standards for gear.

Toward that end there may be info relevant to operating temperature range found in the following UL standards for assemblies:

UL 67 (panelboards)

UL 891 (switchboards)

UL 845 (motor control centers)

In section 27, Molded Case Circuit Breakers (MCCBs) of the Eaton Electrical Consulting Application Guide (CAG), there is a reference to the operating temperature range of molded case breakers built with electronic trip unit (ETUs), where the issue is discussed.

Web link to Eaton CAG section 27: Click Here

Series G - in standard published catalog information for Series G circuit breakers, a temperature range for standard MCCB operation is found in the General Specifications table. Screenshots from page V4-T2-11 of the August 2017 catalog:


Even though a similar table, as above, is not published in the Series C section of the catalog, since the construction/assembly technique and materials used in Series G and Series C breakers are similar, the same overall standard operating temperature range applies to both series of breakers. That range is -20°C to +70°C.

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