Larry, typically not all panels are designed to accept tandem breakers regardless of size. This is especially true of QO main breaker panels. If the lable on the panel does not show tandem spaces, then tandems are not allowed.
Scott, when installed in a panel, there is no visible difference between QOTxxxx and QOxxxx breakers. In fact, the only physical difference is the mounting foot.
What you are describing is the difference between an old style and new style QO tandem breaker. The handle change occured in the mid to late 80's.
edit: changed first line to "not all panels". fingers and brain not always connected.
[This message has been edited by JBD (edited 07-26-2005).]
