Low voltage - Johnson Controls - LIT-12011950 - Building automation software - Smart Equipment Controller - 5.0

Smart Equipment Controls Sequence of Operation Technical Bulletin

Johnson Controls
Product name
Smart Equipment Controller
Document type
Technical Bulletin
Document number
Revision date
Product status

Setpoints and related data

The setpoints and related data include the following items:

  • Outputs disabled due to low input voltage (UCBLowVolt)
  • Outputs limited due to low input voltage (UCBBrownOut)


The input for low voltage is the supply voltage to UCB - UCB 24VAC input (UCB24VForOutp).


The outputs for low voltage are all relay outputs.


The UCB monitors the 24 VAC for low voltage conditions and has two thresholds, one at approximately 18 VAC and one at approximately 20 VAC.

If the UCB needs to turn on a relay output, it determines if the voltage is above approximately 20 VAC before it energizes the output. If the voltage is not above approximately 20 VAC, it holds off additional relay outputs and displays the appropriate alarm on the LCD. Any relay outputs that are already energized continue in that state.

If the voltage drops below approximately 18 VAC, the UCB de-energizes the relay outputs and displays the appropriate alarm.

Note: If W1 is present, the UCB energizes the indoor fan relay output even with a low voltage detected.