Veris - Application Notes: Monitoring Fan & Pump Status

Monitoring Fan & Pump Status

Theory of operation for current switches:

In constant volume fan and pump motors, most of the energy (work) is used to move the air or liquid, with less energy (typically 40 % or less) being used to actually turn the motor itself. The difference between the current draw on an unloaded motor and one which has a load (i.e., is moving air or liquid) can be detected by a current switch sensing the current flow in one phase of a multi-phase motor. Using an adjustable threshold, the switch can operate to provide different status outputs when the motor is loaded and unloaded, thus providing positive proof of flow.

Advantages of Veris current switches over DP's:

Installed cost is lower (typically $20 to $50 per point)
Current switches can be used in either air or liquid applications under any pressure, saving the need for ordering multiple models
Current switches do not require periodic maintenance and recalibration, saving the end user maintenance costs
Current switches are located in the motor control center, eliminating the need for going to the fan or pump which may be located in the ceiling or in some remote location
Current switches offer much longer life, reducing cost of operation

Applications are suggestions. Field applications vary; since manufacturer does not install the devices, it is up to the installer to ensure suitability and compliance to appropriate codes.