Continuous Current Rating
The continuous current rating of a circuit breaker is defined by the National Electrical Manufacturers
Association (NEMA) as: “
The maximum direct current or rms current, in amperes, at rated frequency
which a device or assembly will carry continuously without exceeding the specified limits of observable
temperature rise.� Sometimes referred to as the ampere rating or handle rating of the circuit breaker,
the continuous current rating relates to the system current flow under normal conditions.
UL Standard 489 states that circuit breakers must carry 100% of their continuous current rating
indefinitely (without tripping) at 104° F (40° C) in free air. QOU circuit breakers should be applied, per
the NEC, to carry 80% of their continuous current ratings in the intended enclosure. The continuous
current rating is indicated on the handle of each circuit breaker. See Table 1.
The above is quoted from the following link for a Square D Circuit Breaker Catalog (Underlines & bold font are mine):
http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QOU%20Miniature%20Circuit%20Breakers/0720CT9401R105.pdf.
Edited by: GaPete