Stray neutral current problems and analysis associated with multiple ATS generator installations

Abstract

In generator installations where you have more than one 3-pole automatic-transfer-switch (ATS) on a 4-wire system, stray neutral currents and unwanted magnetic fields may arise. These stray currents and fields can cause a multitude of problems. Magnetic fields created by stray neutral currents can cause objectionable current on the conduit system. Objectionable current of this type can cause voltage rises on the grounding system. Geometries of stray neutral current paths can cause magnetic fields through areas of buildings that may cause problems with sensitive electronic equipment. Ground fault protection devices may detect incorrect ground fault condition. The presence of stray ground currents in multi-ATS installations is dependent on equipment selection and bonding connection points, whereas the magnitude of these currents depend on the system geometry, raceway size/types, and other factors. This paper looks at several stray neutral configurations tested in the Vanderbilt Power Laboratory.