Main bonding screw

[starsandstripes]

I installed a transformer and panel at a guardshack for a high school. The transformer is fed 480 volt single phase from one of the many subpanels at the school, stepped down to 240/120 for lights, heat, and gates for the guardshack. The main bonding screw stays out, correct?

 

[kwired]

I installed a transformer and panel at a guardshack for a high school. The transformer is fed 480 volt single phase from one of the many subpanels at the school, stepped down to 240/120 for lights, heat, and gates for the guardshack. The main bonding screw stays out, correct?

Depends, your separately derived system needs to be grounded, and a grounding electrode needs installed. It can be done at the transformer or the first disconnect, usually can not be both.

 

[tom baker]

For panels in a building or structure, set up as a feeder, a neutral to case bond is not made, with exceptions for a SDS.
For a seperate building, since the 2008 NEC, the neutral to case bond is not allowed. But if you have an SDS, then the neutral to case bond, or green screw is used, at the transfomer or first disconnect. This bond is called the System Bonding Jumper.
And that seperate building feed requires an equipment bonding conductor run with the power conductors, and a connection to a grounding electrode system....