Is there any feature I can look for on a barrel connector to ensure that the outer conductor (the negative terminal in my case) makes contact first before the inner conductor?

I can't seem to find this information, and for the pair we have, it looks like the inner conductor usually makes contact first.

  • \$\begingroup\$ If you already have one where one is guaranteed to make contact first, can't you just switch polarity in your design? \$\endgroup\$
    – PlasmaHH
    May 12, 2015 at 15:40
  • \$\begingroup\$ I don't recall ever seeing a barrel connector where the order of connections could be guaranteed by design. \$\endgroup\$
    – brhans
    May 12, 2015 at 15:41
  • \$\begingroup\$ "can't you just switch polarity in your design" -- on an off-the-shelf power supply?! \$\endgroup\$
    – Jason S
    May 12, 2015 at 15:44
  • 1
    \$\begingroup\$ Probably not. You should make your circuit (something involving the switch?) immune to the order of connections. \$\endgroup\$ May 12, 2015 at 15:45
  • 1
    \$\begingroup\$ Sounds like you may want to consider optoisolating the PC connection. \$\endgroup\$ May 12, 2015 at 16:05

1 Answer 1


In direct answer to your question, I don't think there is. This kind with an all-metal ring around the outside has a chance of working. I'll let you shop for whatever style it is that you need.

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You have an interesting problem. To quote the Wikipedia page:

RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to ±25 volts.

So, one might guess that a 24V connection would be guaranteed to not cause problems, however it appears that (your?) RS-232 level converter is either non-compliant or non-compliant with power off. Charging your power supply capacitor through protection diodes is probably not conducive to the health of the chip.

The cheapest solution is probably to use a different chip and/or put Schottky diodes from the output/input to the +/- RS-232 supplies and perhaps 12 TVSs from the output/input to your circuit ground.

If money is no object, then a DC-DC converter on the input power is another solution, or opto-isolate the RS-232 as @Ignacio suggests above.

  • \$\begingroup\$ thanks but that's not my question. \$\endgroup\$
    – Jason S
    May 12, 2015 at 17:46
  • \$\begingroup\$ @NickJohnson I added that later. \$\endgroup\$ May 12, 2015 at 20:09

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