How can we help you today?

What is a QO, QOB, or QOU high magnetic breaker (suffix HM), and is it marked anywhere on the breaker?

Standard QO115 and QO120 circuit breakers are manufactured to have a magnetic trip point at approximately 8x to 10x the breaker rating. There are some applications, however, in which a load has an inrush current high enough to cause these standard circuit breakers to trip. Examples of these loads include area lighting for athletic fields, parking lots, or outdoor signs. To allow the high inrush current without tripping the circuit breaker, a high magnetic breaker should be used. These high magnetic breakers have a magnetic trip point set much higher than the standard circuit breakers. They can be identified by the HM suffix on the catalog number (QO115HM). Current production HM breakers are also identified with a "High Magnetic" label on the side of the breaker (see photo).
NOTE: The above explanation comparing the standard breaker to the high magnetic breaker applies to 1 pole, 15 and 20 A, QO, QOB, and QOU breakers only. Other ampere 1p breakers and all 2 pole and 3 pole versions are already high magnetic as standard. (Breakers with suffix GFI, AFI, CAFI, and DF are not available as high magnetic).

Picture of HM breaker