allen bradley micro logic 1200 blowing input fuse

[utahspud]

I have an allen Bradley micro running a fan in an industrial paint mixing facility. The input fuse is 3a. The system will run fine for a bit and then all of a sudden the input fuse will blow. There is only .22 amps on on the fuse with the fan running. Anyone have any ideas on what could be spiking in the controller to cause the fuse to blow?

 

[OkiePC]

Is this fuse the input to the Micrologix power supply?
What is the part number of the Micrologix?
Voltage?
Fuse type?

Welcome to the forum!

 

[utahspud]

yes the fuse is the input to the plc
Its a 1200 series micro logic.
120v
Fuse is ATQR3. 3a


I cant ever see more then .22 amps when I am testing. Found out the problem has been going on for a long time, they have just been replacing the fuse daily.

 

[OkiePC]

The inrush current at power up can be quite high for a few milliseconds. The book says 25a for 8ms. You have a time delay fuse, so that is not likely to be the case. Does the input power get turned off an on frequently and if so does the fuse blow when first powered up?

Is that circuit going ONLY to the PLC power supply terminal?

Also, some models have a small 24 volt power supply built into the PLC that can be used to power sensors/switches. Is anything wired to the PLC 24 volt power supply terminals?

 

[geniusintraining]

This may help

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1762-um001_-en-p.pdf

See page 91