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I am building a 5V circuit where the maximum current draw I expect will be 5-5.5A, so have purchased a 5V 6A power supply IRM-30-5ST.

In order to connect this power supply to the mains, I have purchased a mains plug to IEC female power plug along with an IEC male socket with a 250V 10A fuse. I then plan to connect the L and N terminals of the IEC socket to the L and N input terminals on the power supply with 18AWG wires.

Now I have two questions:

  1. Does my power supply have an internal isolation transformer? I have tried searching to see if all Class II power supplies include an isolation transformer, but can't seem to find an answer to this question. There is this post here which seems to imply they do. I have also looked at the datasheet and more information parts from the power supply link above but can't seem to tell if it provides isolation or not for the output.

  2. Even if my power supply does isolate the circuit connected to the output, that still means that the 18AWG wires between the IEC socket and my power supply have high voltage, so touching one of these wires or terminals would be very dangerous. If I put my final complete circuitry inside an enclosure and connect the enclosure to the E terminal on my IEC socket, would this make it safe?

My assumption is it would, because the enclosure prevents touching the 18AWG wires between the IEC socket and the power supply, and if one of these wires frays or becomes loose and touches the enclosure, the connection between the enclosure and earth should prevent a shock. Is my assumption wrong?

Outside of the enclosure though, would an isolation transformer connected to mains and then my IEC plug connected to that protect me from shocks if I touch the 18AWG wires? Would I need this isolation transformer if my 18AWG wires are hidden inside an enclosure where the enclosure is connected to earth?

If I do/should be using an isolation transformer (at least when it's outside of an enclosure aka while I'm building it,) would I be better off getting a power supply like this over the power supply I currently have as that power supply looks like it is inherently safer as there is no exposed high voltage wires (main reason I got the power supply I have is because it was the only 5V power supply my local store had.)

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  • \$\begingroup\$ ”I have tried searching to see if all Class II power supplies include an isolation transformer” They do. \$\endgroup\$
    – winny
    Jun 29, 2022 at 9:05
  • \$\begingroup\$ If you have an isolation transformer and touch both output wires it's MORE dangerous. The voltage will be the same but the isolation will defeat any RCD device in your supply. \$\endgroup\$
    – Finbarr
    Jun 29, 2022 at 9:18
  • \$\begingroup\$ The datasheet for the supply clearly states "Isolation class II" \$\endgroup\$
    – Finbarr
    Jun 29, 2022 at 9:19
  • \$\begingroup\$ @Finbarr so plugging an RCD device into my wall socket, then connecting my IEC plug that powers my power supply into that would provide protection over using an isolation transformer instead of the RCD device? "The datasheet for the supply clearly states 'Isolation class II'" my bad I don't know how I missed that, I also Ctrl-f'ed for it on the page and it said no matches which didn't help my search. \$\endgroup\$
    – Darcy
    Jun 29, 2022 at 9:29
  • \$\begingroup\$ The RCD only provides protection from current flowing to earth through you if you touch one of the live wires. If you touch both wires coming out of the isolation transformer current will flow through you from one to the other and the RCD won't see any problem. \$\endgroup\$
    – Finbarr
    Jun 29, 2022 at 9:41

1 Answer 1

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The entire question is under the scope of IEC 62368-1.

To the 1st question:

It's indicated in the datasheet that the device is an IEC Class II device which means a device having a "double" insulation. Double insulation requires that the device should withstand at least 3 kVac across its input and output, and the datasheet indicates that the withstand voltage is 4 kVac.

To the 2nd question:

By placing the power supply and the circuitry supplied from it into a metal enclosure and ground the enclosure by bonding the PE cable, you make the entire system Class I, which means a basic insulation as well as safety ground.

In either case, you don't need an extra isolation transformer provided that the end-user will never have a chance to access the live voltage "inside" or "around" the product during normal use.

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  • \$\begingroup\$ I get that the power supply itself is insulated and touching it should not shock me, but what about touching the 18AWG wires supplying 230VAC from the wall socket to the two input terminals on the power supply, would the current not flow from wall socket through me to earth bypassing the power supply in this case, effectively rendering the power supplies safety features useless? Edit: looks like your edit "provided that the end-user will never have a chance to access the live voltage 'inside' or 'around' the product during normal use."may have answered my question \$\endgroup\$
    – Darcy
    Jun 29, 2022 at 9:38
  • \$\begingroup\$ Yes; if in normal operation the device is "safe", and the user takes the cover off and hurts themselves / burns their house down, it is their fault for not heeding the sticker which reads "no user-serviceable parts inside - refer service to qualified professionals only." Of course, you could use security screws to make it even harder to get into. \$\endgroup\$
    – rdtsc
    Jun 29, 2022 at 12:02

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