Sizing ATS When Considering Load Shedding

[dbaltazar]

For an optional standby generator with load shedding and with the ATS integrated into a switchboard, must the ATS be sized to the main breaker? For example, say there is a new 4000A-480V-3Ph switchboard (with a 4000A main) to be installed in a commercial/industrial setting, but a 1MW (480V-3Ph) generator with load shedding is to be used to back up this switchboard. As stated before, the ATS will be integrated into the main switchboard; the ATS should be a 4000A ATS, correct? Has anyone seen or worked on a similar scenario? I know NEC art. 702.4 mainly dictates this scenario; are there any other code sections that come into play?

 

[jim dungar]

For an optional standby generator with load shedding and with the ATS integrated into a switchboard, must the ATS be sized to the main breaker? For example, say there is a new 4000A-480V-3Ph switchboard (with a 4000A main) to be installed in a commercial/industrial setting, but a 1MW (480V-3Ph) generator with load shedding is to be used to back up this switchboard. As stated before, the ATS will be integrated into the main switchboard; the ATS should be a 4000A ATS, correct? Has anyone seen or worked on a similar scenario? I know NEC art. 702.4 mainly dictates this scenario; are there any other code sections that come into play?

The ATS needs to be sized for the current flowing through it 4000A in your case. If you were using an Automatic Throw Over scheme, using individual breakers, you could have it built with different size devices.