Application Notes: Monitoring Unit Vents and Exhaust Fans

Monitoring Unit Vents and Exhaust Fans

Theory of operation for go/no switches:

Direct drive motors which control unit ventilators and exhaust fans typically draw either full load amps or no amps. Because these units are either on or off, there is no need for an adjustable threshold on the current switch to detect belt loss. The lowest cost alternative to monitor positive proof on direct drive motors is the VERIS 800 series go/no fixed threshold current switch. The 800 series switch turns on (closes) at approximately 1/2 amp and remains on until the amp draw falls to 0 amps.

Advantages of Veris 800 sensors over auxiliary contacts:

Auxiliary contacts monitor only contact closure from the starter. If a mechanical or electrical failure occurs, the auxiliary contacts will not detect that the motor is not operating.
The Veris 800 switch is looking at amperage and the amp load will be present only if a load is present at the motor
The 800 switch mounts directly in the unit vent or fan enclosure, minimizing the space requirements

Advantages of Veris 800 sensors over DP's:

DP's require setup and calibration and can be difficult to calibrate in low flow installations such as exhaust fans
DP's require cleaning and calibration to maintain accuracy while the 800 switch is solid state and requires no ongoing calibration or maintenance
The small size of the 800 makes it easy to install in tight spaces, while DP's are very difficult to install in a typical unit vent cabinet

The VERIS 800 series is a small current switch designed to mount in the smallest spaces. It requires no calibration, reducing the cost of installation dramatically. It turns on at ~1/2 amp and remains on until the unit senses a drop in amperage to 0 amps.

Installation instructions:

Disconnect the power to the motor on the unit vent
Remove the wire from one phase of the motor
Insert the primary conductor through the center hole of the 800 and reconnect to the starter or contactor
Connect the digital input wires from the automation panel to the output terminals of the 800
Start the motor and verify proper status (off = open; on = closed)

Typical Hawkeye 800 installation in a unit ventilator:

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.