SubMonitor: Overheat and Rapid Cycling Protection

In previous posts, we’ve covered the details of how SubMonitor protects a 3-phase installation from high/low voltage and under/overload conditions. This time around, we’ll cover overheat and rapid cycling.

All motors generate heat. In order to ensure proper operation and maximum life, a motor must be able to effectively dissipate the heat it generates. In the case of a submersible motor, that method is the cooling flow of water that is drawn past the motor by the pump above it. If that cooling flow is interrupted for any reason, the motor can overheat and fail.

Franklin Electric submersible 6- and 8-inch motors labeled “Subtrol Equipped” contain a built-in sensor that can detect and report an overheat condition when connected to a SubMonitor. When an overheat condition occurs, the sensor sends a series of continuous electrical pulses up the motor lead and drop cable. SubMonitor recognizes this signal and takes the motor offline to protect it.

No temperature adjustment is required if an overheat condition occurs; the sensor is pre-calibrated, and SubMonitor’s default setting for overheat detection is ON. If SubMonitor detects an overheat condition, it will take the motor offline for 10 minutes and then attempt a restart. If the overheat condition is still present on the restart, SubMonitor will take the motor offline again, repeating the cycle until it reaches a maximum number of attempts.  Both the time-out and restart settings can be adjusted manually. This time-out setting can be adjusted from 5 to 60 minutes in 5 minute increments (default is 10), and the restart setting can be adjusted from 0 to 10 restarts (default is 3).


SubMonitor also protects against rapid cycling conditions that can occur, for example, with chattering contacts. If SubMonitor detects more than 10 starts in 10 seconds, it will take the motor offline one minute. After that minute has elapsed, it will attempt to restart the motor 3 more times before requiring a manual reset. This setting is also adjustable, but the default parameter generally covers the vast majority of installations.


Even though SubMonitor protects against many of the circumstances that can harm a submersible motor, there are certain damaging conditions to which SubMonitor does not apply. We’ll cover those in our next post.

Note: Even if a motor does not contain a Subtrol heat sensor, SubMonitor will still protect it from high/low voltage, under/overload, and rapid cycling conditions.

One thought on “SubMonitor: Overheat and Rapid Cycling Protection

  1. Hi, Thanks for the info on sub monitor. i need your help on a 2.2KW 400V blac bocs 3 phase intelligent system management serial No; B12975, F.E part number : 382000013 that seems to have been burnt out for one reason or another. I have failed to get a replacement from the local Franklin representative and from the internet too. is it an obsolete piece of equipment that warrants me to get an equivalent sub monitor? If so what model of sub monitor do i need and from where can i source it directly?

    Many thanks for the Frankin Aid articles, they r such an important source of knowledge.

    A merry xmas and a prosperous new year.

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