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Context: I have a robotic arm with a series of servo motors, that together draw up to 3A from my bench supply (depending on the load on the servos). To make it easier to transport the robot around, I've bought the recommended DC power supply from the manufacturer - which just looks like one of those standard laptop power supplies.

Now here's my issue: The new power supply comes with a molex-to-coax cable. The molex plugs into the robot and the coax goes into the new power supply. The coax end is a metal panel-mount jack (!).

Should I worry about the fact that it's metal? I.e. when the servos are working hard, drawing a few amps - is an accidental brush of the jack going to throw me accross the room?

For clarity here's a link to the style of jack I've been given, any advice would be greatly appreciated.

http://minute-man.com/acatalog/Online_Catalog_Metal_Housing_207.html

enter image description here

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    \$\begingroup\$ Assuming the exposed metal is grounded, there should be no problem. (The load on the power supply doesn't matter, it's the voltage that's of concern here.) \$\endgroup\$
    – Dave Tweed
    Apr 15, 2013 at 17:35
  • \$\begingroup\$ It's only 12V but as I say, the servos typically draw a few Amps when in opperation. \$\endgroup\$
    – user9885
    Apr 15, 2013 at 17:39
  • \$\begingroup\$ A link to the power unit would be useful but the voltage is low and you can't receive a shock from the current that's flowing from a 12V supply - 12V won't push 3A through your fingers. \$\endgroup\$
    – Andy aka
    Apr 15, 2013 at 17:56
  • \$\begingroup\$ If you post link to a specific jack you have, we can paste the image in for you. \$\endgroup\$ Apr 15, 2013 at 17:57
  • \$\begingroup\$ Oh thanks that would be great - the website isn't great but here goes: crustcrawler.com/products/AX-18F%20Smart%20Robotic%20Arm you're looking for the 'AX-12A/AX-18A Power Supply' and the 'AX-12A/AX-18A Power Harness' - which is the molex-to-coax cable. \$\endgroup\$
    – user9885
    Apr 15, 2013 at 17:59

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This is generally a non-issue. Exposed ground on panel connectors are standard practice. Most metal devices are grounded, using a Chassis Ground. Those metal AV Stereo Systems at home, computer cases, modems and routers, your car, washing machine, dryer, fridge, all have their metal frame and chassis grounded, usually to the same ground on the incoming power cable. Some specialized equipment (mostly studio audio) do not tie their chassis to the common AC ground, but use a Technical Ground, to prevent ground loops or feedback.

If you ever touch (bare) metal on a car, you have touched a ground connected signal with potentially hundreds of amps in it. Death by electrical shock in a car is practically unheard of. Only 1000 deaths a year by electrocution (or subsequent injuries) in the US, and 30% of those deaths are due to High Voltage Live Wire Issues. 10% involve large home appliances. You have more to worry about from your refrigerator than you do from a small DC servo power supply.

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