ATS Sizing Tool

From service amps or generator kW to the next standard transfer-switch frame — the 125% continuous rule, shown.

Recommended ATS frame

400A

226 A load × 1.25 = 282 A

30407080100150225260400600800100012001600200030004000

Standard frames from the same ladder our sizing engine uses. Withstand/close-on ratings, poles and transition type are an engineering call — verify with a licensed electrician.

Generator size · 150 kW

Voltage

Phase

Sizing from the generator suits essential-loads (downstream) transfer. For whole-building, service-entrance transfer, size from the SERVICE instead — switch the basis above.

Read the ATS guide

This tool is a planning aid. It does not replace final engineering review, AHJ determination, or a formal quote. Verify requirements with your AHJ and a licensed engineer.

New to transfer switches? the plain-language ATS guide