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I have seen a variety of optional or included features with power supplies that the manufacturer calls a safety shield. In some cases it is just a 3 sided piece of metal - the back and bottom remain open, such that someone reaching around the back could contact the bus bars. I see how it protects from a short due to a dropped tool, but do not see how that can be considered a safety shield for personnel - perhaps when operated in a rack, but not when operated on a bench top. What criteria would the UL or CSA standards impose for a manufacturer to legitimately call something a safety shield?

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  • \$\begingroup\$ picture??????????? \$\endgroup\$ – Neil_UK Aug 29 '16 at 18:41
  • \$\begingroup\$ What voltage DC? For a high current 24V supply, you don't need much, but metal still seems like a bad choice. For a 500V Drive output, most manufacturers use a Polycarbonate or other plastic shield that is about 90% touch safe; you can still get to the lugs with long meter probes for example, or your fingers if you really work on it. \$\endgroup\$ – R Drast Aug 30 '16 at 11:00
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I think it would satisfy access to dropping a wrench and electrocuting the holder, criteria and keeping one's fingers out. If it is for industrial use and not consumer use then that should be adequate. Open framed supplies do not have a shield and require additional enclosure.

IMHO, this is just a marketing item to meet customer demand for internal large cabinets rather than a UL requirement for sub-assemblies.

My last design was UL certified but the open frame supply was enclosed with end vents and forced air cooling.

For cooling design I wanted passive vertical vents but was told there were specific checks/tests on the supply inside the 1U high 19" rack mounted unit.

  • Coke spill test
  • sledge hammer test ( sparks or shorts to HV contacts to case.) so insulator was needed.
  • fan locked rotor test (thermal test)
  • Short circuit outputs test. (48V PoE)
  • AC earth to case resistance ( 100 mOhm)
  • leakage current to ground from line filter (0.5mA max)
  • masked areas for safety welded ground stud to spade lug wire before powder coat paint

I was able to get 6 waved since I was able to prove spade lugs relied on the washers,nut & thread yield low milliohm values and did not need not an unpainted bottom surface.

Mostly to look for sparks or flammability or ground leakage current safety,

I am not sure which tests are omitted for an open framed supply that may be used as is or integrated .

  • Anecdote

To reduce cost, many power supply manufacturers are using the CE Mark to indicate compliance with EN 60950-1 rather than pay for and maintain a separate EN 60950-1 test report and certificate. In this case the CB test certificate (and CB test report) will indicate that the product was “additionally evaluated to EN 60950-1”. This is perfectly acceptable.

“The following end-product enclosures are required:” Here the types of enclosures are indicated for mounting the power supply in. If an open frame power supply is being used, the report will state that it has to be housed in an enclosure.

Usually there are three main documents; the CB certificate, an IEC 60950-1 CB report and / or EN 60950-1 test certificate and of course for North America, the UL or CSA 60950-1 test report

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This is covered under IP ratings (IEC60529). The first digit is for objects, the second is water. So ignoring the last digit:

Rating - Protection Against

IP1X - Solid object greater than 50mm

IP2X - Solid object greater than 12.5mm

IP3X - Solid object greater than 2.5mm

IP4x - Solid object greater than 0.1mm

IP5X - Dust. Minimal dist ingress permitted.

IP6X - Dust tight. No ingress.

RS - IP Ratings Guide

So therefore in theory you would want one at least IP3X or greater if possible to obtain, the problem then is it seems they are not often tested unless the manufacturer is making a dust or water resistant part. So I guess it's a bit of extra effort they've gone to.

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  • \$\begingroup\$ "Finger safe" is IP 2X. \$\endgroup\$ – Li-aung Yip Dec 6 '16 at 2:44

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