To fuse or not too fuse!

kapooski2012 · Sep 13, 2012

Hi there folks,
Just realized, after testing the small thermal 1.2 amp breaker I was planning to use on my PLC trainer is no good. I have several in-line fuse holder I can use. I guess I have a choice of slow blow, fast acting or ceramic and what would be the best....and if I start adding all the amperage of all the output plus the operating current of the PLC (which I could not find in the manual, unless I was looking in the wrong area) I imagine a fuse no bigger than 1.5 or even 2.0, but if were to go up to 3 or 4 would I melt or fuse something lol ? Plus I built the safety project that Ron Beaufort designed below adding my twist!
I dont how to add an image through the url, therfore I made it an attachement compliments to Ron Beafort, (hope I didn't break any copyright laws)

jrwb4gbm · Sep 13, 2012

As long as the devices and wire current carrying capacity is rated at higher than the fuse current carrying value, everything should be ok. Slow blow fuses are used on devices with high inrush current, fast acting fuses are used on electronic devices, most small ceramic fuses have a higher design voltage rating than glass type.

GlennA · Sep 13, 2012

Depends on how good your nerves are. I decided to fuse each output at 250 mA on a PLC intended to go to South America. My rationale was that an inexperienced tech could blow several fuses during troubleshooting, instead of the transistor output. What kind of outputs does your PLC have ? And how good are your nerves ?

kapooski2012 · Sep 14, 2012

I decided to go with the 2 amp fast acting on the line side, some else sugested that I put an additional 5 amp fuse on the output side...this is where it is a little confusing! I'm not sure exactly were that is, got any pictures? That is worth a few fuses.

GlennA · Sep 14, 2012

This attachment (if it uploaded) is how I fused the outputs of an Omron CP1L plc. The outputs are sourcing transistors so the +24 DC (also fused at the power supply) goes to the output commons.

Lancie1 · Sep 16, 2012

...if I start adding all the amperage of all the output plus the operating current of the PLC (which I could not find in the manual, unless I was looking in the wrong area) ...

Check the manual Appendix Page A-3. It appears that your PLC draws about 19 Volt-Amps or 0.16 Amps at 120 volts AC. But note that the in-rush current can be as large as 30 Amps for 8 miliseconds. That probably will not blow a 2, 3, 4, or 5 amp fuse, but it depends on how many solenoids, relays, and contactors that you connect on the MicroLogix 1000 Output terminals connected to the same 120 volt source.

Also check the Input and Output current requirements on pages A-4 and A-5. Your twelve relay outputs are rated for 1.5 Amps each max break current, so make sure whatever you connect to each of these PLC outputs does not exceed 180 VA.

Micrologix 1000 1761-L32AWA Power Usage.jpg

kapooski2012 · Sep 17, 2012

It is pretty obvious that I was looking in the wrong area,

believe it or not I own a hard copy of that book somewhere.

thank you so much.

Now I have a laptop dedicated only for PLC, it's going to be good,

Thank you everyone

To fuse or not too fuse!

kapooski2012

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jrwb4gbm

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GlennA

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kapooski2012

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GlennA

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Lancie1

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kapooski2012

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