Fan Safety Alarm Circuits

Noah Smith
4 min read
RIBMNLB FamilyYou've got an Air Handling Unit (AHU) in need of a fan-safety-shutdown. You need to isolate field devices from your building automation controller. Your middle name is Alan. If any of these things are true, you've come to the right blog post. If all three of these things are true, that means our mind reading technology is working.

RIBMNLB

The first product in Functional Device's line of Fan Safety Alarm Circuits is the RIBMNLB. RIBMNLB combines all the relay logic to facilitate fan status, fan safety control, and damper actuator control. It is intended for use in a circuit that will control fan start/stop and fan safety shut-down circuit monitors three critical inputs:

  • Low-limit freeze protection (to stop fan and remove power from damper actuator)
  • Static pressure (to monitor for hi/low pressure condition)
  • Smoke detector / fire alarm

One aspect of the RIBMNLB that can be applied to more general use cases is the isolation of field devices from the building automation controller. The logic table below is the default configuration of the RIBMNLB. However, it can be simply reconfigured in the field to monitor normally open inputs or disable unused inputs.

Dry Contact Inputs
(From Field)
Isolated Dry Contact Outputs
(To Controller/Fan/Actuator)
Low Limit Static Pressure Smoke Detector/FA Master Relay Low Limit Static Pressure Smoke Detector/FA
CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED
OPEN x x OPEN OPEN x x
x OPEN x OPEN x OPEN x
x x OPEN OPEN x x OPEN
OPEN OPEN OPEN OPEN OPEN OPEN OPEN

Other Fan Safety Alarm Circuits

We offer a range of other Fan Safety Alarm Circuits to meet your needs. Only have two inputs? Take a look at the RIBMNLB-2. Have 6 normally open inputs? Take a look at RIBMNLB-6NO. Need BACnet capabilities? Take a look at RIBMNWLB-7-BC. While all these devices offer similar functionality, having a device that's sized correctly and has the correct logic directly out of the box can save on valuable space and time. If you're interested, be sure to check out the linked datasheets to see all the extra features such as latched inputs and 24V sourced outputs.