Sizing an automatic transfer switch downstream of a standby generator starts with the continuous and non-continuous load schedule, not with the generator kVA. Calculate the design current, apply the applicable diversity and duty factors, then select the ATSE frame whose rated operational current covers that current at the ambient temperature of the switchroom. Confirm the short-circuit withstand of the ATSE against the prospective fault current at the point of installation, and verify that the switching device is coordinated with the upstream and downstream protection.
Source & Authority
This guide is maintained by the engineering team at MOTE Electric, a China-based ATSE manufacturer supplying critical infrastructure projects since 2003. Product specifications referenced are based on IEC 60947-6-1 and internal type-test reports.