In our research lab we are setting up a VFD to run an experiment.

The power comes into the building through a 45 kVA, 240 V, three-phase transformer and the project will be powered from a 240 V three-phase outlet connected to a 40 A breaker.

From the outlet it will run through a 15 kVA, 240 V - 480 V three-phase step up transformer to power a 15 kW VFD which will drive an 8 kW motor.

Should I be taking arc flash preventative measures for this such as enclosures or cabinets? Cabinets are really expensive and this is a test bench, not a permanent installation. I'm not sure when the point is where risk of arch flash becomes intolerably high.

  • \$\begingroup\$ @AndrewMorton So at that power level is it an arc flash risk? I don't know where the line is drawn. Because from what you're saying even a 1HP VFD plugged into a single-phase 120V outlet would need its own cabinet and I doubt that's the case. \$\endgroup\$
    – DKNguyen
    Commented Apr 1, 2022 at 21:56
  • \$\begingroup\$ My comment was not based on firm knowledge, so I retract it. But could you put the DUT in another room with no people in it? \$\endgroup\$ Commented Apr 1, 2022 at 21:59
  • \$\begingroup\$ @AndrewMorton By DUT do you mean the motor? Or the whole package, step-up transformer, VFD, and all. Because we could just put the motor off somewhere else (no one wants to be near this thing when it's running anyways). We could even physically isolate everything. The issue is that the keypad on the VFD is right on the VFD and isn't that the point that is most likely to flash? That or the transformer but you don't have to stand next to the transformer to turn it on. \$\endgroup\$
    – DKNguyen
    Commented Apr 1, 2022 at 22:02
  • \$\begingroup\$ Don't forget to securely fasten the motor... :-) \$\endgroup\$
    – Antonio51
    Commented Apr 2, 2022 at 8:16

1 Answer 1


You want a professional with relevant experience involved in the design. It should be an electrical engineer with a professional license, practicing in the field of low voltage distribution and switchgear design.

You'd be doing yourself and by extension your employer real disservice by not consulting someone who knows what's what. Mistakes in these matters cause loss of health and potentially life, and often loss of life is the preferable outcome, as loss of health usually involves disfigurement and extensive loss of function.

A 15kVA 3-phase transformer on a low impedance supply circuit can produce 1MW arc heating before protection kicks in. It's arguably perhaps a worst case, but even a well controlled 15kW arc is not something you want in your face.


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