What is a Service Entrance-rated transfer switch?

A service entrance-rated transfer switch is a transfer switch that contains an integrated disconnecting device and meets the grounding and bonding requirements of the National Electrical Code for service entrance use.  

The salient features of an ASCO service entrance-rated transfer switch are (1) an integrated circuit breaker provided on the Normal side of the ATS, (2) a bonding jumper between the neutral and ground, and (3) a neutral disconnect link.