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Anthony Coker

Technical Services Manager North Georgia District

Schematic examples of the Safety Chain for RTU’s – Part 2

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On the first Tech-Tip we went over the R looper wire which went through Pins 7 and 8 on  UCB Main like below as well as the LSM.

In this Tech Tip, we will go over Pins 7 and 8 again with the red looper wire as well as go over the one with the UCB going to a (VFD) Variable Frequency Drive.

Example 1: 48FC 04-07 RED LOOPER WIRE

Details for Example 1:

  • 24vac from transformer
  • UCB Main Pin 1
  • UCB Smoke Shutdown A
  • UCB Smoke Shutdown B
  • UCB Remote Shutdown A
  • UCB Remote Shutdown B
  • UCB Phase Monitor (PMR) A(24v)
  • UCB PMR B(CONT)
  • Main Pin 7
  • Just a RED wire in a loop from UCB Main Pin 7 to Pin 8
  • UCB Main Pin 8

You now have R!

Note: The yellow letters are between Pin 7 and 8 on UCB Main!

Note: Check all voltages to ground.

Example: 24VAC Transformer Secondary to ground. Then UCB Main at Pin1 to ground then

Smoke Shutdown A to ground etc, etc…

If you have voltages all the way to Pin8 on UCB Main then you will have Voltage on R terminal.

Example 2: Commercial Air Handler/ 40RU 410A with VFD
  • 24vac from transformer
  • UCB Main Pin 1
  • Smoke Shutdown A
  • Smoke Shutdown B
  • Remote Shutdown A
  • Remote Shutdown B
  • Phase Monitor (PMR) A(24v)
  • PMR B(CONT)

NOTE: Everything with yellow letters is between Pin 7 and 8 on UCB Main in this example

  • UCB Main Pin 7
  • PL12 Pin1
  • PL1 Pin8

ACS320 Drive, which has orange boxes around it in the photo below.

The ACH180 is the yellow boxes which will use Terminal 6 that will be the drive that we use for this example.
The ACH550 and the ACH580 will be the blue boxes which will use Terminal 25. I just want to make sure you see how they have written the numbers. 

On the picture above you have VFD Drive Terminals.
RO1 Relay Output 1 Source which is either
(NO) = Normally Open which is Power off or
(NC) = Normally Closed which is Power on.
All of this is inside the VFD drive. Now we will leave the VFD drive and head back to the UCB Main Plug to complete our circuit.

Now check voltages from these pins to ground.

  • VFD Drive ACH180: use 7 which is the RO1 Relay Output 1 Source in the VFD Drive.
  • PL1 Pin 11
  • PL12 Pin2
  • UCB Main Pin8

Now you have voltage on R!

Disclaimer: The technical statements, information and recommendations contained herein are believed to be accurate as of the date hereof, but Mingledorff’s does not make representations or warranties, express or implied, as to its accuracy, its completeness, or the results to be obtained. The information is being provided for informational purposes only and is intended for use by persons having adequate skill and expertise regarding the proper selection, use and application of the products and recommendations and at their own risk and discretion. 

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