Application Notes: Fan & Pump Status with Integral Start/Stop

Fan & Pump Status with Integral Start/Stop

Theory of operation for current switches with integral command relay:

Combining a current switch and relay into a single package allows the user to monitor the positive status of a fan or pump and to control the operation of the fan or pump from a single device. The current switch detects mechanical or electrical failures by providing a binary output change if the amp draw falls below a pre-set level (see "Monitoring Fan & Pump Status" for a more complete description). The integral command relay provides a start stop output (up to 1200 VA) which is activated by a 24 V signal from an automation system. The normally open contact on the relay closes when the digital output on the automation system closes, enabling the magnetic starter to close and starting the motor.

Advantages of combination devices over discrete switches and relays:

Space required for installing the devices is greatly reduced as the footprint of the combined device is the same as the current switch alone
Electrical subcontractor cost is lower as the wiring between the automation panel and the motor starter is all low voltage
Hardware cost is lower for a combined device than for separate switches and relays
Electrical conduit costs are reduced as all wires can be pulled in a single, low-voltage conduit and a separate line voltage conduit is not needed

The VERIS 735 current switch/command relay device is the industry's first multi-purpose current switch and relay. The 735 is the ideal solution for the automation installer as it combines the status and starting functions into a single package, dramatically reducing the space required for total control of fans and pumps. Hardware, labor and subcontract costs are also lower, providing a cost effective and efficient solution to the need for control and feedback of most fans and pumps. The current switch provides a status level signal to the automation system while the relay provides a contact output capable of switching almost any contactor.
Combining the industry-standard Hawkeye 700 technology with a relay output provides total control over fan and pump operation for virtually any HVAC installation.

Installation Instructions:

Current switch:

Mount the 700 series current switch on one phase of the motor between the mag starter and the motor (typically in the motor control center) - the 700 series products are all UL 508 listed devices for field mounting
Adjust the potentiometer until the "Output Status" LED just switches on;
Turn the potentiometer CCW ~ 1/4 turn;
The unit is now calibrated to detect mechanical or electrical failures

Command relay:

Wire the digital output from the automation panel to the input terminals of the 735 - this connection is low voltage (24 V AC/DC; 10mA nom.)
Wire the two flying leads from the output of the relay to the coil side of the motor contactor
Verify operation of the relay by issuing an "on" command to the digital output of the automation system

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.