The series of columns on automatic transfer switches (ATS) that ran April through June 2001 generated more e-mail than any previous topic, including some insightful questions. I thought two in particular deserved a follow-up:
A reader took issue with my position on the use of three-pole switches on four-wire systems, stating: "Your article suggests that three-pole switches with solid neutral bars [should] never be used due to '...electromagnetic interference from currents flowing in the ground, and can interfere with the proper operation of ground fault protection systems...' Manufacturers have been selling three-pole automatic transfer switches without switched neutrals for 120/208 and 277/480-V, three-phase, four-wire systems for years without incident. Personally I've been selling them for over 20 years. Please provide me with your insight as to why we should discontinue using these switches in applications without ground fault protection."