I'm building an automation control panel. It uses a 120VAC to 24VDC power supply to power several IO cards and signal lines. The entire system will draw less than 500mA when in operation.

This PSU is rated to output 24VDC at up to 5A. The sticker also states that it draws up to 2.6A on the input side.

I have already installed a fuse on the input side, rated for 2A.

Should it also have a 5A fuse on the output? or will the 2A input fuse open if the output is overloaded/shorted?

What is the best practice in this situation?



1 Answer 1


The power supply is most likely already protected on the primary side. Check the spec sheet.

Since your secondary load is quite small compared to the capacity of the secondary, a best practice is to install secondary protection at the planned load in order to protect the load elements and associated wiring, rather than the supply.

  • \$\begingroup\$ The specs say "Protections: short circuit, over voltage, overload, over temperature" so does this mean the output side is protected against overcurrent too? Wonder if this is a single failure fuse or resettable safety? \$\endgroup\$ Jul 7, 2017 at 2:11
  • 1
    \$\begingroup\$ The idea of adding a fuse on the secondary side is to protect the devices connected to the secondary side. If a device or its wiring develops a short, the supply will route up to 5 amps into that short. This could cause more damage. The additional fuse limits this current to say 0.75 amps in order to protect the devices and wiring on the secondary side. It is not required, but it is a best practice. \$\endgroup\$
    – Glenn W9IQ
    Jul 7, 2017 at 12:15

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