Barry is not, despite my best efforts. However, he is the best Commander training guy around!
Here is what he said:
The split main bus was a response to the European requirement that ALL buses have protection. The main bus was split and given CB protection. Those airplanes have bus ties, which you are familiar with their operation. They also have main bus ties which are always in and only trip when there is an issue with the main bus or possibly a generator. The benefit to the split main bus system is we can now isolate the batteries if there’s a problem there and continue to run the electrical system off of the generators respectively.