PLC Fuse

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plc fuse

The fuse goes inline on the 24 vdc supply to plc. I prefer to use small circuit breakers. Circuit breakers are really convenient when doing maintenance. Otherwise any 4 amp fuse rated for 24 vdc OR Greater voltage is fine. If the inputs are not supplied from the plc they should be fuse protected at their source (this would be an uncommon configuration).

it would be common to use fast acting fuses for circuit boards

time delay fuses for motors

different boards can be more or less tolerant to abuse

more protection is better than less

it gets real expensive when a motor shorts out & ruins the output board

there can be issues with compliance with regulations, that require protection devices

the best configuration, depends on many factors including

duty cycle, type of load & common configurations on other equipment in your facility

Ok Sujinvipin you want to know why to use a fuse, depending on the application i would possibly use a seperate fuse for each I/O.

The reason that I would do this is for easy identification of where a problem circuit is, if the fuse is blown I is that input that is causing the problem, this can and will reduce trouble shooting time on time critical equipment.

Cheers

Joe

Doesn't it depend upon the size of the wiring? The wiring is, after all, what the fuse is there to protect!

The fuse comming from your power supply should be capable of handling the output current of your power supply and not be too large a value for the wiring you are using. Generally a slow blow fuse is used here.

Ideally each input should be fused seperately with a 0.5 amp fuse. However in a practical world I might use 1 fuse for as many as 4 inputs. Make sure that each input can be disconnected easily for troubleshooting reasons. If an input shorts it can pull down the power suply to 0 Volts and if it's not fused correctly this can be hard to find.

Each and every connected output should be fused. 0.5 amps for 24v and 2 amps for 120v. This is to protect the output triacs or relay contacts from failure in a short circuit condition. These values are general values, your needs may differ.

You can do with less fusing, but it will cost you more in down time and repairs.

What you are protecting is the power suply from overload, and your output cards from excessive current. You don't want to have to replace a card because of a short circuit in an attached device.

Good luck Elroy