Is this Cutler-Hammer Breaker meant to have a double tap?
No they are not.
Sorry guys, those are not double taps. Those are tandem breakers. Notice the two handles and labels for off/on.
Yes but did you notice on the upper breaker the TWO wires on the same lug? That IS a double tap
In addition, there is one copper wire and one AL wire.
Sorry, on the tablet it looked like a shadow.
Question - not knowing what came first , the black or red wire on that double tap . But since its not run as a 240 volt or multi wire circuit ( need another breaker to join the two so its using 2 different poles - as the small diagram shows on the face of the breaker) . Its very possible the addition of that red wire may be incorrectly working on the same pole if its part of one of the other 2 black wire circuits. Does that red wire use the same neutral ( white ) as one of those black (hot) wires ?
Well done looks like I and others did not see what you saw this could certainly make for a well overloaded neutral .
The neutral would be an issue if both hots were from the same cable.
I think you mean from same phase ,They could be different cables .
Doesn’t matter if it’s a tandem breaker in this case.
The double tap is still under one lug.