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I'm building a nixie clock kit with these instructions. I'm up to the part where I have to test (page 17) the high voltage components (the power supply is 12V 250 mA) which is up to 170 volts (page 5) and is potentially lethal. Now I don't know if they put that disclaimer just to cover themselves or if there's really a likelihood of killing myself assembling a nixie clock kit.

I've done some electronics back in high school a few years ago but I'm no electrical engineer or electrician so I'm wondering what kind of safety precautions I should take? I don't suppose dishwashing rubber gloves suffice?

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    \$\begingroup\$ Very good question. In my opinion too many people rush into working with HV (or mains for that matter), without being aware of danger. This question shows you are aware and awareness is the most important part to working safe. \$\endgroup\$ – jippie Jul 3 '12 at 7:43
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That supply could very easily kill you.
That said, I've (long ago) had a number of shocks at that level with no long term ill effects - BUT some people manage to die on the first encounter. Try not to ever find out which category you will be in. (I've also had numerous 230 VAC mains shocks and a few at around 1000 VDC with in all cases never more than a nasty experience at the time.The last was long ago and I aim not to repeat them if at all possible.) (230 VAC is probably the most "disturbing")

A DC supply has a "can't let go" effect clamping the muscles. You don't want to EVER experience this.

HV is not something to worry about overly much - but must not be ignored. You may be able to receive say 100 shocks in quick succession from such a system and suffer no consequesnces apart from nightmares and a lifelong aversion to digital clocks of any sort. BUT it could kill you along the way.

Anything in the area outlines in red in the diagram below will be potentially lethal and anything outside it MAY be :-).

enter image description here


Historical advice is to keep one hand in your pocket while testing to prevent accidentally closing a hand to hand circuit via you chest/heart. That has some merit BUT slow deliberate thought out actions are at least as valuable.

Rubber dish washing gloves would offer very substantial protection if dry and not punctured. Puncturing can happen on a small wire end. They can be used as an added safety feature and PROBABLY make things much safer BUT act as if you are not wearing them.

If I "MUST" work near live conductors I try to keep fingers curled inwards so that a hand clench triggered by current will not cause grasping of a live conductor. Brushing the back of a hand against a live HV conductor is liable to cause a muscle contraction towards your body BUT do not ever rely on this.

Best method is to have HV turned off until it is needed for testing.
Think what you are going to do, and have tools, meters etc ready.
If you can attach a meter with a test clip with power off, so much the better.
If a test clip will not safely and reliably attach to the HV target you can solder a wire to HV when power is off (of course) and connect that to the meter probe. After you have experience with such things you are liable to think nothing of measuring say 230 VAC mains or 500 VDC with two probes with power on - but resist the urge to leap in an do what will be safe enough wit experience until you have some experience - or you may never acquire any :-(. It's really rather safe most of the time. But it's better to be safe than sorry as a beginner.

Power on, think, test, think, power off.
Be SURE power is off.
Be SURE power is off.
Be SURE power is off.

I have seen power on when it was thought to be off happen often enough over the years that I am quite obsessive about checking. If a mains cord is involved I am liable to turn power off, pull out plug, wave the cord to be sure the plug is the correct one, place plug near gear being worked on as an indication that it is safe. That's obsessive. I'm alive.
I recently installed a new domestic stove in place of an old one for a friend, with only a wall mains switch between me and mains. Fuse still in for various reasons. "Safe enough" but potentially lethal. Tested with meter. Shorted all leads (PNE) together to ensure no mains on.
Treated all wiring as if alive as much as possible throughout job. Obsessive. Alive.

Think carefully. Act slowly. Being very safe is easy.

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  • \$\begingroup\$ Thanks for the advice. imgur.com/VdTzj,fFhHs is what it currently looks like. i.imgur.com/fFhHs.jpg is the location of the HV and GND on the PCB. What do you mean by have the HV off until testing? I don't have anything plugged in to the HV, 5V, and GND holes and plan to have a multimeter needle on the GND and HV with both hands... would it be better if I get some wire to plug in to the board and then get alligator clips to attach the multimeter to the other end of the wire? Not very experienced with this so just making sure of the proper steps/precautions. Thanks :) \$\endgroup\$ – Jack Jul 3 '12 at 5:40
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    \$\begingroup\$ @Jack - note that the components and tracks connected to HV as highlighted by the red box on my diagram are far more extensive than the single point that you note. | See my somewhat 'enhanced ' answer re connections and powering. With experience this is a trivial matter. Your job, if you choose to accept it, is to last long enough to become experienced :-). \$\endgroup\$ – Russell McMahon Jul 3 '12 at 7:31
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    \$\begingroup\$ Maybe good to mention that capacitors can be charged to a high voltage well after being disconnected from mains. Best to discharge large capacitors and measure the voltage across them. \$\endgroup\$ – jippie Jul 3 '12 at 7:40

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