BQ was their long standing bolt-on breaker, Siemens replaced it in panelboards with the BL, QP, plug-in, E2, 240V, E4, 480V, E6, 600V.Looking into a 1982 Speedfax catalog, it looks like ITE used EQ to designate their 240V max breaker line, which they called 'normal duty'. They used ET for their 'heavy-duty' 600V products. Then you had the specific breaker type like BQ, E4, QP etc.