SparkyNC:
The Devices I believe you are referencing are the "Sub-Feed" types, which are placed on the actual Bus Kit its self; as opposed to being connected to the Bus Kit via Lug Landing Studs + Breaker Mounting Accessories.
The QO/QOB Line of "Sub-Feed" Circuit Breakers, for use on NQOD Bus Kits, use the Standard Catalog Numbering Protocol as a typical QO/QOB Device, with the letters "SL" preceding the Frame Designation.
For example, a Two Pole, 90 Amp Sub-Feed Plug-On Device would be Catalog No.: QO290SL
The Three Pole version of the 90 Amp Sub-Feed Plug-On Device would be Catalog No.: QO390SL
For the Bolt-On (QOB) versions of the Sub-Feed Devices, the Catalog Numbers will be QOBXXXXSL
Catalog Number examples using the 90 Amp Trip Rating:
QOB290SL for the Two Pole Bolt-On,
QOB390SL for the Three Pole Bolt-On.
The Plug-On Sub-Feed Breakers will have Two Sets of Clips, so the Device connects to both the Left AND Right side Bus Tabs.
The Two Pole versions will have a total of (4) Bus Clips, and the Three Pole versions will have a total of (6) Bus Clips.
The Sub-Feed Breakers look like a typical QO/QOB Device (Trip Handle, Trip Indicator, Mounting and Bus Tabs, Frame width and height, etc.), except they extend across the full width of the NQOD Bus kit.
Sub-Feed Breakers are completely different from the Designated "Main Circuit Breakers".
These are the "QOM1" and "QOM2" Series of OCPDs, which do not attach to the Bus Kit at the Branch Device spaces; instead these Devices are separately mounted at One "End" of the Bus Kit, and have Terminals which attach to the Bus Kit in lieu of Main Lugs.
The Line Side of these Devices have Lugs, which Terminate the incoming Feeders.
"Sub-Feed Breakers" and "Main Circuit Breakers" have completely different appearances and characteristics, it would be nearly impossible to mistake the two device types.
Main Circuit Breakers would be considered as "Bolt-On Only", whereas Sub-Feed Breakers may be either "Plug-On" or "Bolt-On".
Sub-Feed Breakers mount on the Bus Kit, in the Spaces designated for Branch Circuit Breakers (the Distribution Bus Section);
Main Circuit Breakers are mounted separately (remotely) from the Bus Kit, and Terminate to the Bus Kit at the "Mains Section" only.
--Scott (EE)
