Switching the Neutral Conductor

Automatic Transfer Switches (ATSs)
are available with and without a dedicated pole to switch the neutral conductor of load circuits between Normal and Emergency power sources. This paper describes the function of switched neutral contacts together with considerations for their use. Although the examples shown herein describe options for three-phase systems, the same concepts also extend to managing the neutral conductor in single phase systems.

Three pole transfer switches are used to provide basic load switching operation for three-phase backup power applications. These switches transfer the three phase conductors between the Normal and Emergency power sources. In this application, the neutral conductor of the Emergency source is bonded to the neutral conductor of the Normal source using solid neutral plate mounted within the ATS, and the building ground serves the entire power system.