Commercial building owners may own or lease transformers and substations. The types of connections and secondary voltages will be different.  They will be based, in part, on the primary use of the building. 

With commercial electrical systems, it all starts with the transformers and sub-stations. An inspector cannot perform a proper inspection until the type of system and its voltages are known. It is common for large buildings to have multiple substations. In some cases, there may be multiple substations so the distribution equipment can be as close as possible to the loads served.  Industrial facilities, for example, often have substations at multiple locations.  

Another common arrangement is to have two substations physically connected together but operating independently of each other during normal operation. They can be electrically connected together by way of a tie breaker.  This arrangement, called a double-ended substation, has some advantages over a typical single ended substation. In the event that one transformer fails or needs to be taken out of service for maintenance, the adjacent substation can continue to supply electricity to the entire system. 

In a perfect world, every transformer would have a readily accessible and legible nomenclature plate with a one-line diagram and Voltages listed. The plate may be there but you may always be able to read everything that is on it. It helps to be able to look at the connections to determine what type of system it is.  Small and medium size pad mounted transformers are are usually enclosed so looking at the connections may not be an option. You should be able to access the service equipment and determine the system characteristics there.

The quizzes in the transformer series will give you a glimpse into the variety you will encounter among commercial electrical systems. When you are consistently able to score in the 80% range, you will have the knowledge you need to feel confident and to be successful in the field.