What is the low side rating that would typically have a center tap that is not split?

The low side rating that typically has a center tap that is not split is 240/120. This configuration refers to a split-phase system commonly found in residential and light commercial buildings. In this setup, the center tap provides a neutral point, allowing for both 120-volt and 240-volt circuits.

When using a 240/120 rating, the split phase allows 120 volts to be taken from each of the two hot wires (each providing 120 volts to neutral), and when combined across the two, it allows for 240 volts. The arrangement does not "split" the center tap, as it simply acts as a neutral point, making it ideal for multiple common household applications, such as lighting (which typically uses 120 volts) and larger appliances (which may require 240 volts).

In contrast, the other ratings listed do not employ a standard configuration that includes a center tap in the manner typical for 120/240 systems, or they represent voltages not usually seen in residential installations, leading to their exclusion as fitting answers for this question.