Is the line side of a 400amp. Trans S on the top or the bottom lugs?

What is a "trans S cabinet"?

Line is always on top.

A "Trans "S" is a combination meter/CT PLUS a disconnect switch in one single enclosure. They are rated from 200amp through 800amp and the line side can be either on the top or bottom, depending on how you feed the equipment. It's a common form of installation here in the NYC area.

Let me ask you a couple of questions:

(1) Are you a licensed electrician? If not stay away from a 400 Amp panelboard!
(2) Are you allowed to install the meter up side down in NYC?

Usually, the feed to a meter is at the top of the meter.

From the meter to the Main Breaker can be either top or bottom, depending on the way the cabinet must be installed.

The original question was posted Feb 2008.

I would hope the installation is done by now.

All anyone had to do was a search for Trans S meter, seems Con Ed uses these, combination CT cabinet and test meter all in one cabinet.

http://www.coned.com/es/specs/electricbluebook.pdf

http://www.coned.com/es/specs/electric/Section%20XV%20-%20Spec%20755.pdf

http://www.coned.com/es/specs/electric/Section%20XV%20-%20Spec%20195.pdf