What modern 20 amp breaker is compatible with my Challenger panel?
TLDR: Replace every breaker in your panel with a BR type from Bryant, Cutler Hammer or Eaton, readily available most places that sell breakers.  Nothing else should be in your panel - especially not a Challenger (unless you like fires)! 

For the best answer ever on this subject, see here.



Green highlighting added. The breakers don't actually have that.

You must use UL-listed or UL-classified breakers

UL-listed means the manufacturer of the panel makes the breakers using their internal knowledge, and UL certified it as safe. 

UL-Classified means a competitor reverse-engineered it.  UL has torture-tested it and confirmed it safe. 

Never stick random Brand X breakers in your panel. The bus stabs are different for patent reasons, and will arc and burn when heavily loaded.  We call these "alien breakers". 

Challenger is cursed...

Because of the need for backwards compatibility, one cannot change a bus design. But it's a good bus design. Unfortunately Challenger hopped on the FPE/Zinsco crazytrain and made some very bad breakers for that good bus.  That is why Challenger is on the same "remove it" list as FPE/Zinsco, but only insofar as the breakers, not the panel. 

... but Challenger is blessed.

This industry runs on mergers and acquisitions.  Challenger/Westinghouse wound up in the hands of Bryant who promptly fixed the breaker problem. They changed its name to BR, so they could outlaw use of the defective Challenger Type C breakers. (The buses remain the same).  As for BR breakers, they cross-listed those Type C, since of course they fit Challenger.  This gives Challenger panel owners a super easy upgrade path; simply swap out the vile Type C for Type BR/C for about $5/circuit. 

To be clear: BR/C isn't "UL-classified" for your panel.  It is "UL Listed" for your panel.  And your only legal choice. 

BRyant got folded into Cutler Hammer who got folded into Eaton.  The buses are still the same to maintain backwards compatibility and because the original bus is perfectly fine.

You must change every breaker in the panel to BR type

Since the Challenger breakers are dangerous, every breaker in your panel needs to be a Type BR/Type C from Bryant, Cutler Hammer or Eaton.  If it's not, change it now. 

Also, where your breaker has failed, look closely at the bus stabs under the breaker.  Challenger never had a bus-stab problem, but lots of people don't know about the BR/C thing, so they run out and grab any "alien breaker" like a Square D HOMeline or GE or Murray.  Those could have burned up the bus.  A burned bus is unusable; that space is permanently dead. Search the panel for any other alien breakers and get rid of em.  

An alien breaker can be a sleeping monster; most circuits aren't loaded very hard (until they are, and that's when it fries).