GE PowerMark Plus GE Breakers
GE breaker part numbering explained

GE loadcenter-type breakers come in various flavors, but there are a few things in common.  First off, all the part numbers start with "T" -- this is likely because the line was acquired when GE picked up an upstart breaker maker called Trumbull Electric.  The next one or two letters (H, HH, X) designate the interrupting rating of the breaker -- the normal H designates a standard residential 10kAIC breaker, with a few exceptions to be noted below, while HH and X are used for higher interrupting ratings found in commercial work.  Some very old (Trumbull-era) breakers lack this letter in their part number, indicating they are only rated to 5kAIC -- this is a good indication they are obsolete.  The next two (or occasionally three) letters indicate the type of breaker:


QL denotes the standard "Q-line", plug-on-type, 1" wide breaker
QD denotes a "double-wide" (4 slots in a 2x2 pattern) breaker used for 150-225A ratings -- these breakers are 10kAIC unless denoted with a raised interrupting rating by a single H in the part number.  They are cable-in/cable-out types by default, although they are available as plug-on types as well, denoted by a "QDL" in the part number.
QP denotes a "half-width" (1/2" wide), plug-on-type breaker (GE's equivalent to what's called a "double-stuff", "cheater", or "tandem" breaker).  These can only be used in slots that specifically permit them.
QC denotes a cable-in/cable-out type of breaker, used for applications like subdivided protection for large electric heating loads.  Instead of plugging into a panel to get their power, they have a lug terminal on each end and thus can be used in a situation where there is no busbar to plug on to.


Following this letter prefix for the breaker type/series (what you see on the labeling on your loadcenter), there is 4 or 5 digit part number:


The first digit denotes the number of breaker poles present
The second digit denotes the voltage rating of the breaker, save for THQP's which lack it and are always 120/240V as a result.  It will always be 1 on breakers used in residential work, for a 120/240V slash rated breaker (120V line-to-neutral, 240V line-to-line).
A few devices will have letters after the second digit, to denote unprotected switching -- you probably won't run into these.
The remaining digits in the part number specify the trip rating (amp rating) of the breaker.


Any designations after the amp rating indicate special breaker features, such as ground fault, arc fault, or dual function (arc &amp; ground fault) protection.  (There are others as well, but you generally won't find them in residential work.)

Specifically:


GFT denotes a current-generation ground fault breaker (the T here is for self-test functionality as per the current UL943)
AF2 denotes a current-generation combination arc fault breaker (AF was used for the previous generation of GE combination arc fault breakers -- the differences are fairly subtle and only impact multi-wire or 240VAC branch circuits)
DF denotes dual-function breakers that combine arc &amp; ground fault protection


Of course, not all part numbers are made -- check a current GE breaker catalog for details on what you can get.