150 amp and larger split bus panels were available with two separate lighting sections, but they were not very common. I've only seen maybe a dozen of them in my 30 years in the business and they were usually being removed. Split bus panels have become so rare nowadays, that newcomers to the industry have never seen them. That's probably a good thing. I tend to think that most of these panels were 100 amp with a single lighting section. Many people who aren't familiar with them often question why they were ever made. On that note, I'll throw in my two cents worth about them:
The real reason for split bus panels was to reduce the cost. 60 amp breakers and below are relatively inexpensive in comparison to 100 amp and above. By using a 60 amp "lighting main", plus the various five other two-pole breakers in the "main" section, the need for a large main breaker is eliminated. Remember that it's legal to have up to six disconnecting means on a service. This setup makes the other two-pole breakers become service disconnects instead of branch breakers. Again, it was all just an effort to eliminate the cost of a main breaker.
Supposedly, the only breakers that were allowed to be in the main section were ones for larger loads, such as ranges, air conditioning, heating, dryers, etc. The problem with these panels was that Harry Homeowners would see these vacant spaces and assume that they could use them for their own branch circuits. By using single-pole breakers in these spaces, it was possible to have as many as ten disconnects (branch circuits) IN ADDITION to the two-pole lighting main.
Then, there was also the misconception that turning off the "lighting main" killed power to the house. People didn't realize that all breakers in the upper section of the panel had to be turned off to truly kill the power.
