Ground without continuity??

Some time ago I bought a grounding wrist strap, with wrist contact on one end on the inside of the strap, wire connection to alligator clip. I always put it on and clip it to the chassis when working inside a machine.

I had had my meter out to check a house wiring circuit and afterwards set it on my desk.

It was sitting there when I was going into my machine, and I thought I would check it for continuity at the alligator clip, make sure contact though case. It checked out ok, and as an afterthought I put the meter on the case and on the wrist contact. Much to my surprise, there was no continuity.

Put the meter on the alligator clip and the wrist contact. No continuity.

Punctured the wire, no continuity behind the wrist contact.

Moral, if you use one of these, check it!

Martin

 

Before you throw it away, be sure you had your ohmmeter set on the proper range. Depending on the type of wrist strap, there is either a 50 Kohm or a 1 megohm limiting resistor in series with the wrist strap lead to protect against electrocution of the user. You don't actually want a DIRECT ground of the user. I think most ESD straps use the 1 megohm limiter.

If you are using a digital meter without auto-ranging and have it set on too low of a range, it'll indicate no continuity.

 

Hey Surferdude: Well, I sure don't want to electrocute myself, I'm really not ready for that great beyond.

Meter is analog with needle scale for measurements. Get off scale reading wire to alligator, after close examination, needle has almost imperceptible movement wire to wrist strap contact. Does not reach 1megohm I see no inline bulge that would indicate resistor. Maybe resistor wire?

So you think it is adequate to dissipate static?

I wasn't going to throw it out, I was going to solder a lead to wrist strap contact, but having second thoughts after your post.

Martin

 

No doubt I've saved your life so I'll expect a little something in the mail for Xmas.

Without a doubt, for maximum security from tampering.

The 1 meg limiter will protect you all the way to 10 kvolts, assuming you could die with 10 ma. current across your chest (normal assumption). You'll not likely be exposed to any potential of that magnitude working on computers. If you do, call me first.

Best regards.

 

Hey Surferdude, I really do owe you at least one! Send me your address and a wish list. Of course, I owe everybody on this board one.

Board been used for a lot of things, but I'll bet it is the first time it saved a life!!!!

I guess I was setting myself up to be fried. I never mess around in there with power on (except in absent minded events, fried a drive like that) but unless resetting the CMOS, I don't unplug before sticking my hands in there.

But truly, is there enough voltage/amperage to fry a person in these infernal machines? Never even gave it a thought, always just worried about static electricity.

Thanks again,

Martin

 

Unless you get inside the power supply or any line voltage switch loop lead, you're relatively safe inside the computer. Given that 12 volts is the normal high voltage, you would need to reduce your body resistance lower than is possible to receive a lethal current flow.

 

Potentially 12V is enough to stop your heart, but only if it coincides precisely to a certain period of your heartbeat that effectively cancels out the heartbeat electrical activity. Very unlikely but it does happen.

I was shocked to hear at a first aid course a couple of years ago that a few people die each year (not sure if that is Australiawide or worldwide?) from sticking one of those 9V batteries on there tongue. As a school kid I used to regularly do that to see who could keep it there the longest.

I'm glad I obviously got the timing with the heart beat wrong.

Scarry stuff!

 

Hey Surferdude, since you and Paul have convinced me that my risk of electrocution inside the box is 0 or less, my offer of an Xmas present as a reward for saving my life is hereby withdrawn. Instead of sending me your wish list, I would suggest you send it on to Santa Claus at the North Pole.

It's not that I don't appreciate good advice and learning, but I do have to put some kind of value on what I have learned and judge the rewards accordingly.

Martin

 

Martin, you're a generous guy..........

Similar Thinking

Food for thought How much does it cost to ship one half of Catastrophy to Hobart, Australia and the other half to Moose Creek, Illinois? Guess one would have to consider the return freight costs too - when they don't accept delivery. I'll reimburse you for the actual shipping charges and then you won't be out of pocket for anything. Ho Ho Ho ..... (I'll Bet Johanna would do the gift wrapping too)


edit after Martin's post below - First I'd have to figure out how to convince my own. Talk about an impossible task ........ Gheeeeezz!

 

Rockster: You have made it clear you are a great judge of character! Now, if you could just convince my wife..........

Martin

 

Now, you know I don't come to Hardware very often, but I do get perverse pleasure and entertainment observing Catastrophe's relentless evil torture to Martin. But I get this image of Martin sitting around with alligator clips and voltage meters, wondering about his electrical tolerance level, and then picture Paul sucking on batteries, and realize SD2 has already done all this, out of male curiosity, and I instinctively understand why your Missuses needs convincing of probably everything!

Then another voice chimes in- Hey Rockster! Just 'cause I'm a woman doesn't mean I do the GIFT WRAPPING!! Give me an HOUR with Catastrophe, ALONE, and I will show her who is boss! Ha!

Now, you bone heads, listen up! You may be able to build a nuclear reactor at the kitchen table with duct tape and soup cans, but that does not mean your wives are going to appreciate your genius, especially if you use any of the important kitchen utensils.

Kingdoms have been won and lost over women, the hand that rocks the cradle rules the world. You guys couldn't find your socks without our help. Knowing you guys, and your low tolerance for inadequate hardware and performance, I'm sure you all chose competent smart wives. I'm also going to assume that they would be just as disturbed by the image of their husbands experimenting with static discharge as I am when my husband announces he will be using his arc welder on the toaster. (Gift wrapping? she mutters under her breath!) Give those ladies some credit- after all, they put up with YOU battery tasting electrical fools!

Johanna

Admit it, Zander is right, you men can go alone into the woods and still be wrong!

 

Johanna, it is not Catastrophe, it is Catastrophy.

You cannot scare her. She's bigger than you are! Probably weighs more too.

Martin

 

Like I said, Don't ask Johanna to gift wrap it. Nope - Dont even think about it.

Phew, good thing I edited my post a couple of days ago, changing the e to a y, huh? Guess it's a guy thing ... eh, Martin? I'm outta here - headed to the back 40 to see if Zander found safe refuge and whether or not he'll sell me a little piece of that real estate.



Open mouth, insert foot - Rockster.

 

I think the purpose of the wrist strap is not quite understood. It is not designed to protect you - it is designed to protect ESD (electrostatic discharge) sensitive devices - such as memory chips and CPUs. It is designed to prevent a buildup of static in you. If you stuck your hand in the power supply and came across the AC input, don't count on that strap saving your life. You should have had the PC unplugged!

The important thing to realize is that the threshhold of awareness for static discharge (AKA spark) is higher than the tolerance of some ESD sensitive devices. That means a tiny shock from your finger tips can destroy an ESD sensitive device without you even knowing a shock occurred!

 

Oh I think Martin understands the purpose of an ESD strap quite well. He just didn't understand the purpose of the inherent series resistance that was incorporated in the design to keep him from frying himself if he made an error in judgement.

Safety first prevents death and litigation, the latter often being the most painful of the two.

 

Was a spelling error at first, after discovering the error, decided to leave it that way as a reminder to myself that I'm not perfect. Got to keep that ego under control.

Martin

 

Rewrite:

Safety first prevents death and litigation, the latter always being the most painful of the two.

 

My spelling stands corrected. Sorry, Martin, meant the Lady no disrespect. But, let me get this straight, I spelled it right and got it wrong? That's been my luck lately.

Johanna

 

Yep!!

You must have been out in the woods with Zander.

I won't tell anybody.

Uh-o, Rockster was out in the woods with Zander, your post drove him there. If he saw you there he'll tell everybody.

Not your lucky day for sure.

Martin

 

Hey Rockster: I have been noticing your new Avatar. I was just wondering, did you have your wrist strap attached before you crawled inside the machine? Wouldn't want to see anything unfortunate happen to you.

Also, it looks like you might need some help, I can come over and see if I can extricate you.

Kindest regards,

Martin