I'm redesigning a board made from another person. This board have several AC/DC converters (like Traco TMP07 Series and similar) and some screw connectors to connect external devices. Neither the converters now the devices have any connection to the Earth, though they are all isolated.

The board have two fuses for each converter output: one on the positive line and on on the "negative" (actually the 0V).

I'm wondering if it's worth to have two fuses on the same current path or it's enough to put the usual one on the positive line.

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    \$\begingroup\$ What are the fuses protecting? That is fundamental to know. \$\endgroup\$ – Andy aka Sep 2 '18 at 9:07
  • \$\begingroup\$ The external devices are other electronic boards, most of them MCU based and low-voltage (5-12V). There's also a 5V analog camera powered from one of the converters. \$\endgroup\$ – Mark Sep 2 '18 at 9:08
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    \$\begingroup\$ Are you convinced that the fuse is designed to protect those external devices? What did the orignal designer say they were for? \$\endgroup\$ – Andy aka Sep 2 '18 at 9:12
  • \$\begingroup\$ Well, actually they should protect the whole line. I mean, if a device fails, the fuse(s) must avoid an excess of current on the wires. The converters have built-in protections against short-circuit. \$\endgroup\$ – Mark Sep 2 '18 at 9:16
  • \$\begingroup\$ I believe that the fuses are probably necessary, not necessarily to protect both legs of the circuit from the same current, but when something was cross connected to either line it would still provide protection. \$\endgroup\$ – K H Sep 2 '18 at 9:31

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