1 Generator 3ATS 2 Separate Utility Sources

[Russell White]

Being asked to provide a design where one generator will feed three ATS. Two of the ATS normal power is from one utility drop and the third remaining ATS normal power is from a separate utility source. Have done multiple ATS downstream from a generator before but never with (2) separate utility sources. Concern is if one ATS calls for emergency power and the other separate utility ATS has not we will end up with both normal and emergency power in a ATS at the same time. Have concerns someone could get hurt in this condition and trying to find if there is any code violations here. Appreciate the help.

 

[Russs57]

I see no issues from a safety point of view.

Assume your standard installation with multiple ATS's. In what way would things be different if you tripped a normal power breaker feeding a given ATS? All the other ATS's would have both normal and emergency power under those conditions.

Now I did think it used to be an issuse to have one particular wing of a building supplied from different a utility source but I am seeing it done now. To be clear I'm talking about something like a hospital with two POCO vaults supplying two different "wings" built at different times. Vault A used to feed wing A with feeders A, B, and C. Vault B used to feed wing B with feeders X, Y, and Z. Now some EE comes along and value engineers so an existing ATS in wing A now supplies a load in wing B....meaning normal power now comes from a POCO vault and normal switch board in a different "building". Can't say I approve but nobody cares what guys at my level think.