Bill,
If Murray has redesigned the bus in their panels, then neither the listed nor classified breakers made for the older panels would be permitted to be used in the new panel. If they made a big enough change to be able to patent the new bus and breaker design, they will be able to prevent any one from making "classified" breakers that fit the new panel. I believe this is exactly what happened with the Square D QO breakers. That bus design is unique and was patented by Square D. There were no third party breakers available for that panel for many years. Now there are "classified" breakers that can be used in the Square D QO panels. I assume that this is because the patent has expired.
Don
