In addition to every function of OSS-T3, TB3 Type ATS, OSS-TO, TBO Type ATS has additional function of Overlapping Neutral Contact. (ON-ON Type ATS)

Function of Overlapping Neutral Contact
When general ATS will be transferred, Arc will be generated between fixed contacts and moving contacts. Thus, current flows between contacts and arc will be eliminated when current will be at zero level. Eliminating time of arc is 10~12ms. Therefore, various device of load side can be protected when neutral contacts should be opened 10~12ms later than other 3-phases contacts. Load side devices of general ATS cannot be sufficiently protected because opening time gap between neutral contacts and other 3-phases contacts is less than 10ms. In order to solve this problem, Overlapping between neutral contacts of A-power (Normal) and B-power (Emergency) during transfer of switch functions to protect various devices of load side more safely. In addition, Non-linear load increases the earth potential and potential difference is occurred between earth and neutral line. When general ATS will be transferred, Neutral line is separated from load and reference potential difference cannot be established. Thus, Floating is occurred and electronic devices can be malfunctioned. When ATS with overlapping neutral contact will be applied, Floating can be protected.
N-phase Transfer
Limits of 4P Transfer