The Square D QO 100 Amp Main Breaker 24-Space 24-Circuit Convertible Outdoor Plug-on Neutral Load Center for Plug-on Neutral and non-CTL tandem breakers is UL Listed for residential, commercial and industrial power distribution. This breaker box has 24 spaces with a maximum circuit capacity of 24 circuits when using non-CTL QO tandem breakers. This load center is built with a shielded, copper bus bar that is plated for reliability. QO load centers are tested and listed only for QO circuit breakers. QO load centers are the "World's Finest" designed with industry leading features for flexible application. QO load centers include features engineered for fast installation and wire savings.