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I'm building a small ICS-like process automation system that will be housed in an ABS enclosure with a clear latched and hinged door. Inside the enclosure is a small peristaltic pump powered by 24 VDC.

I want to power the enclosure with a standard appliance cord through a knockout on the bottom, using a cable gland for stress relief. The cord gets connected to 120 V utility power and inside the box there would be a DIN rail with a Meanwell 120 VAC to 24 VDC power supply and a 24 V relay that uses an external control signal to operate the pump. The DIN rail would be grounded to the mains circuit via the appliance cord and the 24 VDC devices would share an isolated ground.

Are there any requirements for enclosures like this from the NEC or another organization? Anything I’m missing for safety purposes when using DIN devices inside an enclosure?

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  • \$\begingroup\$ Not sure of NEC specifics, but I would expect any live terminals to be shrounded. If the enclosure requires tools to access, then that might be different \$\endgroup\$
    – Kartman
    Commented Aug 23, 2022 at 8:28
  • \$\begingroup\$ "a clear latched and hinged door" Is the latch also lockable? It should be necessary to use a key or tools to open the enclosure so there is no accidental access to live terminals. \$\endgroup\$
    – Graham Nye
    Commented Aug 23, 2022 at 13:42

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What you describe is a pretty common application. The only enclosure requirements I'm aware of would be IP class (the first digit) according to IEC 60529, which applies in case there are exposed live mains inside the enclosure and someone could stick a finger inside through an opening in the housing. You'd then have to do an IP test to ensure that can't happen, to comply with directives like EU LVD directive. Meanwell modules should already comply with all such requirements.

But since you are using a cable gland rather than a soldered, panel/chassis-mount connector, and since DIN modules likely use terminals where you connect an isolated wire, this isn't likely to be a requirement. As long as the cable insulation is peeled correctly and the 120VAC isn't exposed anywhere.

In an industrial environment, one usually wants a reasonably good housing (IP6x) regardless, to keep out dust etc.

I believe safety ground connection of the DIN rail is unnecessary, since the housing isn't conducting. So there's no obvious reason why you'd electrically connect the DIN rail to something at all in this case.

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  • \$\begingroup\$ DIN rail mounted components may be using the rail connection to ground for EMC. So, connecting the DIN rail to earth isn't a bad idea. \$\endgroup\$ Commented Oct 7, 2022 at 17:17
  • \$\begingroup\$ @NickAlexeev It all depends on if there is an enclosure and how it is grounded. If it's a plastic housing and no chassis ground, there's no obvious reason to connect the DIN rail to the safety ground. \$\endgroup\$
    – Lundin
    Commented Oct 10, 2022 at 6:26
  • \$\begingroup\$ Some DIN rail mounted modules connect to the DIN rail. They expect that the DIN rail is grounded, and they use the rail ground for EMC control. [It's not an obvious reason. It's a more subtle reason. Something to keep in mind.] \$\endgroup\$ Commented Oct 10, 2022 at 14:21

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