ioannis_tsi

Should i fuse the 24VDC OUT? In case of a short circuit? And if yes 0.5A is ok since the maximum out is 0.3?

<ioannis_tsi>  

Personally I would never use the 24VDC output given by the PLC..
with the exception of test bench scenario.

My doubt is that the 24VDC given in this way is probably connected to the PLC internal voltages and problems may occur if this voltage is pulled low(er) than the expected voltage. There is less doubt in what the external power supply gives for protection level. The market place have small power supplies available that is cheap when considering the peace of mind the internal protection of such power supplies give.

To refresh what Mr. Jeff said (and adding to it):

Jeff Casagrande

Thank you for the correction.  I normally separate my inputs and outputs on separate breaker supplies (with monitoring) so I can do an orderly shutdown in case of power supply short.

Elsewhere there was mention of putting a bigger than needed power supply into a system. What is important is that you keep in mind to what amp rating the cabling can handle. For you it may not apply now and the protection built-in for the smaller power supply would be enough.

Having a 20A power supply where 0.33mm^2 cable is used (example), can cause wire melting if there is a short to ground. Therefore keep in mind to fuse devices in small enough groups as to not damage cabling if short to ground do occur. In fact... that is what Mr. Jeff is saying in short.

I hope these thoughts are helpful in the future.
w