Thermal Overloads

Just a very quick post on thermal overloads and the dangers lurking within some of the functionalities available.

You would no doubt have seen that there is a manual or auto selection available on the front of the overload unit. When set to manual, it means you have to reset the overload by pressing the reset button. When set to auto however, the unit will reset once the bi-metal strip has cooled down.

This is where I get concerned. How many times has the overload tripped and reset itself? How are you going to know that there is a problem on the installation if it keeps on resetting itself? Fair enough to say that you would need to start the unit again but what if it is a pump that will start automatically? This means you may not find out that there is a problem until it is too late!

Another addition to the thermal overload is the adding of a reset magnet. This unit clips onto the overload and when powered, it activates the little plunger and resets the overload. In my eyes this is a far safer method of resetting the unit from a remote location. The magnet can be activated via a relay driven by and output on your PLC. This means you can reset the unit and if it should trip again, you can investigate it before trying again

This leads me to another point. Do Not just reset the unit when it has tripped. There is a reason for the motor drawing too much current and you need to check the installation first. And lastly, as per the previous post on the thermal overload, never turn the setpoint up because it keeps tripping!

Told you this was a short post!

Till next time, stay safe and keep up the good work

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