Ballast with a switched gray wire?

[zappy]

Hi, I was changing a ballast when I noticed this ballast. If you look at the diagram on the ballast, it shows a switched gray connected to the neutral. I was just wondering what is this all about? Thank you for your help.

 

[Fred B]

A disconnecting means shall be provided that also disconnects the grounded conductor.
410.130(G)(2) Disconnecting means.
(2) Multiwire Branch Circuits.
When connected to multiwire branch circuits, the disconnecting means shall simultaneously break all the supply conductors to the ballast, including the grounded conductor.

 

[zappy]

A disconnecting means shall be provided that also disconnects the grounded conductor.
410.130(G)(2) Disconnecting means.
(2) Multiwire Branch Circuits.
When connected to multiwire branch circuits, the disconnecting means shall simultaneously break all the supply conductors to the ballast, including the grounded conductor.

So what is the grey wire for? There is a white wire already.

 

[CoolWill]

I found this picture pertaining to this ballast.

 

[infinity]

It allows you to switch on and off a certain number of lamps.

 

[don_resqcapt19]

It seems strange that you can accomplish the number of lamps selection by connecting the gray wire to either the white or black supply conductor.