[brian john]

From MXSLICK at Mike Holt

The Pushmatic breakers aren't necessarily unsafe. They do have one drawback in that the original ones only have thermal trip mechanisms and do not have an instantaneous magnetic trip mechanism. In real world terms that means they won't react quite as fast in the event of a short circuit, but their overload response time is average.

The main drawback is that old ones tend to fail mechanically, ie they won't reset after a trip or if you turn them off. So far I have only seen and heard of them failing "safe", as in not turning back on as opposed to FPE and Zinsco which stay closed into a fault. 😁

The little "on/off" indicators also go bad and stay stuck in either position or just rattle around loose.

UBI makes replacements (at $40+ EACH for single pole) which seem to have more robust mechanisms, but I don't know if they have magnetic trip added to them.