Mercury switch units, by their design, are less precise than snap switch units. Because of this, they have more tolerance and the setpoints are less likely to be affected by the system operating pressure and fluctuating water lines. This is related to the linkages that hold the mercury tubes and the rolling effect of the mercury itself.

Snap switch units are more precise. When the water level rises or falls beyond the setpoints, the switch quickly changes state. There is no mercury or linkages to compensate for the subtle movements of the float. Because of this precision, the settings appear to be less than they really are.

The electrical ratings (120VAC/7.4FLA) of both the mercury and snap switch units are the same. Mercury switches have been used in applications where the current loads exceeded the specified ratings. Due to the inherent characteristics of mercury, they worked satisfactorily, with few failures for a limited time. Snap switches, however, are less tolerant of higher current loads and will likely fail if installed in applications that exceed their ratings.

The setpoints on the snap switch units are not designed to be adjusted in the field. The differential between on/off is a function of the micro-switch, which is pre-set. The range is set at the factory using the bracket screw that rides on the micro-switch lever arm.

Keep in mind there are differences. This is due to the inherent nature of the switches and the types of systems where the units are installed.