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 Post subject: Keep ESD black plastic tools out of HV areas
PostPosted: Dec Thu 25, 2014 10:55 pm 
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Recently I was wanting to tweak the neut. cap in an HF transmitter that is tube based and runs a rather high 800-900V on the anodes. There is an opening in the cover for just that purpose. So poking in my stack of tuning tools for a larger one to fit the slot, I came across a black plastic one that should fit. Apparently this is black due to it being impregnated with some sort of substance to bleed off static and be ESD safe, though it is not marked as such. But I have seen such advertised. Anyway, I got on the cap to turn it and at some point the side of the plastic tool contacted the anode of a tube. Well I got a nice shock as well as getting big blue sizzling arcs between the tool and the opening. Yow. Killed power after letting go of it to put an end to this conflagration. Powered back up and nothing damaged but my pride. Later found a yellow tool of identical shape but shorter that would still reach the cap, it worked fine. So beware of black plastic tools made for ESD protection in solid state and low voltage apps. They may look like a big resistor to HV!


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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Dec Thu 25, 2014 11:48 pm 
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A good point that never occurred to me. Too bad you had to find out the way you did. :)

Bill


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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Dec Sat 27, 2014 1:26 am 
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Yes, it was quite a shock if not a thrill. Obviously the resistance of the tool was high enough that it was not a terrible shock but a real eye opener type. Left a little burn mark on the side of the tool, but it is still good for other stuff. Since I don't think it was out and out carelessness on my part I felt I should warn others in the unlikely event. Unless I was taking too much for granted feeling a plastic tool is a plastic tool.


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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Dec Sun 28, 2014 1:01 pm 
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At work, one of my duties is to periodically clean and measure the resistance of the components used at the ESD stations. The mats and wrist straps are about 1M ohm. Wonder if the tools like you used are the same resistance? I suppose they could be measured to see but it does make sense that they are conductive. Thanks for the tip!

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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Dec Mon 29, 2014 5:54 am 
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Great tip, thank you..and just in time.

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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Dec Tue 30, 2014 1:38 am 
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Thank You for the post.

Literally, you may have saved someone's life.

I know I never would have given it a second thought and just grabbed a "wiggle wrench" that fit.

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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Jan Mon 05, 2015 5:49 pm 
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This is exactly why all ESD mats, wrist straps and tools have a 1 Megohm resistor:
1. To prevent electrocution (there is 120 or 220 volts AC everywhere)
2. To prevent a surge that would damage ESD sensitive devices, when there is a static charge on the part or board. They want the voltage to drain off gradually, the resistor protection is for the equipment as well as the user.
No ESD equipment should be used with energized circuits.

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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Jan Thu 08, 2015 12:21 am 
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Saw your post over on eHam, glad you shared it here as well. That is something I never thought of myself.

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 Post subject: Re: Keep ESD black plastic tools out of HV areas
PostPosted: Jan Thu 08, 2015 1:46 pm 
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Bikenswim said,
Quote:
No ESD equipment should be used with energized circuits.
He is exactly correct. We discovered this fact at work quite by accident when a couple of us experienced "tingles" due to a faulty mains ground while using a soldering iron, ESD mat, and ESD wrist strap. We became the "grounding wire" between the soldering iron station and the ESD mat!

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