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What is the proper way to fuse and switch a power supply consisting of a bunch of SMPS like the following:

smps power supply

There would be up to 5 separate output voltages. The outputs shown are about 35W each. Other outputs would be less.

So currently I have a mockup that has a single fuse and a single switch on the AC load line.

Is this safe?

Would it be better to use a 2 pole switch to switch in both load an neutral? Why?

Should I fuse each SMPS separately? If yes, why and where?

Points labelled A, B, C and D are potential locations for reference.

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So currently I have a mock-up that has a single fuse and a single switch on the AC load line. Is this safe?

The majority of devices found in the home or office are wired this way and there are few issues. The problem is that if you live in a land of non-polarised mains plugs which when reversed, can make the non-switched wire live, then the internal circuitry remains live even when the switch is off. A table lamp, for example, has a single-pole swtich and the terminals are exposed when the lamp is removed. Your setup should be much safer if boxed up properly.

Would it be better to use a 2 pole switch to switch in both load an neutral? Why?

When the switch is off both lines are cut and the circuit is completely dead.

Should I fuse each SMPS separately? If yes, why and where?

Check your SMPS and you should find that there is a fuse on the mains side of each. The main fuse protects the wiring inside your unit in the event of a fault. Your SMPS units will supply a total of about 100 W so will draw a max of 130 to 150 W fully loaded. In 110 V land this will be about 1.5 A and in 230 V land it will be less than 1 A. Use a 2 A or 1 A fuse as appropriate in the common live line, point 'A' as you have correctly shown. This will limit any fault current to a much lower and safer value than your mains wiring can provide.

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  • \$\begingroup\$ The SMPS is (or like) MeanWell LPC-35-1050. The datasheet does not indicate that there is any kind of fuse but there is short circuit and overvoltage protection. And since it's constant current, I'm guessing at some point the voltage would just drop to 0? \$\endgroup\$
    – squarewav
    Aug 12 '16 at 21:09
  • \$\begingroup\$ Yes, in normal operation the output is current limited. The fuse is to protect in case the PSU itself pulls excess power. I checked the datasheet and you're right - there's no mention of the internal fuse. \$\endgroup\$
    – Transistor
    Aug 12 '16 at 21:32
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I would use a single switch and fuse as you have shown, particularly if the supplies have internal fuses.

Whether the individual supplies should be switched will depend on the application.

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