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Author Topic: Dangerous AC situation in reception hall - PLEASE READ  (Read 152703 times)

Russ Davis

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Re: Defecation Occurs
« Reply #170 on: September 04, 2013, 02:10:18 pm »

...by the time I could get to her and chase her down it was gone to doggy toy heaven without a trace.

PLEASE post a picture of the Fluke chew-toy.

If "without a trace" means what I think it does, it'll need a thorough cleaning once it reappears.
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Mike Sokol

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Re: freak accident? help!
« Reply #171 on: September 04, 2013, 02:59:05 pm »

A few 'curious' observations from my year-old Fluke Volt Alert 2AC (90-1000V) (always on, but with a battery test button)

1) Anywhere within two inches of my Macbook Pro wallwart and it lights up
2) Anywhere within about 4 inches of my MacBook Pro laptop it lights up
3) Anywhere within an inch of my Apple Airport Express and it lights up
4) On a cheap outlet strip (9 outlets spread over 30 inches) (that is plugged into a GFCI outlet) it doesn't light up anywhere, including inserted into the hot legs, but the outlet strip powers devices.  The GFCI 'source' tests fine.  I haven't opened up the outlet strip (yet) to see how it is wired.

On a dozen other outlets around the house it seems to work correctly.

I've recently done some tests on iPhones plugged into Apple chargers, and found much the same thing. Basically, anything without a ground plug (double insulated) plugged into a wall outlet will bias up to around 50% of the line voltage. So depending on which way you plug in your wall wart, you'll likely measure 40 to 80 volts on chassis of the appliance or gear. Now, this isn't normally dangerous because the double insulation keeps the leakage current through you to less than 1 mA (I think UL limits are 0.5 mA, if memory serves).

However, if your wall wart becomes damaged (dropped too many times) or wet (dunked in the shower), then I do believe it's possible for this double-insulation to fail, which will pass the line current into you. And if you're on something nicely grounded (or standing in the shower like that woman in China last month) and reach out to pick up your iPhone while plugged into a wall charger, then you can die from electrocution.

Again, 2 or 3 mA is a small shock. 10 mA is a big shock. 20 mA you can't let go of the conductors. 30 mA your heart goes into fibrillation in a few seconds. 100 mA nerve damage starts and death is almost certain. Since your body has about 1,000 ohm hand to hand or foot, then it's easy to do the math and see that 30 volts AC can cause 30 mA of current to flow through your heart. Without immediate CPR and AED intervention, you're now dead.

I just won't touch anything directly plugged into an ungrounded wall wart while standing in water. Way too dangerous for me, and I've done some pretty crazy technical things.

Much more on this later, but I'm so glad you brought up the point. Yes, you're iPhone is indeed at 60 volts AC while holding it to your ear while plugged into a wall charger. The current limiting of the insulation is the only thing keeping you alive. Pretty scary when you think about it.

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Jonathan Johnson

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Re: freak accident? help!
« Reply #172 on: September 04, 2013, 04:27:48 pm »

#1)  I don't trust Always On testers. These are the types that don't have an ON/OFF switch, but which start buzzing/beeping when finding a charged surface. Since there's no blinking light to tell you the battery is OK and the unit is in "on" mode, then it's possible to have a dead battery which means the unit won't light up near a wire that's actually on. This is a modern trend towards destupification (that should be a word) since the manufacturer assumes we're too stupid to push the ON switch.  :P

...

#4)  Don't put yourself in a Faraday cage or isolate yourself from the earth. I think this is what gives these NCVT "death sticks" such a bad rap. The manufacturers say that standing on a fiberglass ladder can isolate you enough from the earth so that a NCVT won't beep on an active wire, but I've not found that to be the case. All of my testers beep just fine while I'm on a ladder. However, I've also not tried this in a attic to be sure, so that would be an interesting experiment. Also, if you're inside a charge box (like an RV) then pointing a NCVT at a water faucet inside the RV won't cause it to beep, because your body and the test surface are at exactly the same voltage. Duh!! But standing on the RV steps and pointing it out at the ground WILL make it beep. Which makes perfect sense when you think about it.  ::)

...

6)  I look for a NCVT that's rugged enough to stand up to being thrown in a toolbox, so the Fluke VoltAlert (not their always-on model) and the Klein NCVT-1 (not their dual-sensitivity model) are my favorites right now. Amprobe is sending me some of their newest products to test soon, and if it meets my above criteria, that could be another favorite.  :)

I don't remember the model, but I have what must be one of the first non-contact voltage detectors on the market. If memory serves me correcly it was marketed by Gardner-Bender, but all markings have long since worn off. I think it's only good for AC. I've had it for at least 15 years, maybe 20. Alas, this model isn't made anymore.

It has no power switch. It has no battery test. It's always on. It flickers when you bump it against something. It rattles around in my toolbox. I last changed the batteries 10+ years ago and it still works.

I can stick it in the hot side of an outlet and it lights up, even when I let go of it. It doesn't depend on the capacitance of my body. That's useful when I need to identify a circuit. I've had others, but this one has always been the most trustworthy and my favorite.

But before I use a tester, I always test it against known conditions. Nobody hears the watchdog that doesn't bark.
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Dan Mortensen

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Re: freak accident? help!
« Reply #173 on: September 04, 2013, 06:35:17 pm »

I had a table-top full of different brand NCVT's, and have indeed built a calibration standard using a Variac feeding different size charged surfaces and wire types. While I've not done a formal survey, I've noted some trends.

#1)  I don't trust Always On testers. These are the types that don't have an ON/OFF switch, but which start buzzing/beeping when finding a charged surface. Since there's no blinking light to tell you the battery is OK and the unit is in "on" mode, then it's possible to have a dead battery which means the unit won't light up near a wire that's actually on. This is a modern trend towards destupification (that should be a word) since the manufacturer assumes we're too stupid to push the ON switch.  :P


Hi Mike,

First, thanks for this great thread! I missed it the first time, and am glad you revived it.

Thanks to you, I'm in the process of buying a bunch of non-contact testers and socket testers for my crew.

You said the above today, but in June you found this:

I've just received a care package from Amprobe for more of my testing, and really like their little VP-600SB VoltProbe. Not only is it on all the time (they tell me a year or more battery life) it runs on two standard AAA batteries. Plus it not only beeps (loudly) and blinks (brightly), it also shakes in your hand when it triggers. Plus it's sorta flat with a pen grip to stay in your pocket. I found it at Sears for less than $14  http://www.sears.com/shc/s/p_10153_12605_SP101A11576S6083631101P?sid=IDx20070921x00003a&ci_src=14110944&ci_sku=SPM6045437007


What changed?

Thanks,
Dan
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Mike Sokol

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Re: freak accident? help!
« Reply #174 on: September 04, 2013, 07:29:19 pm »


You said the above today, but in June you found this:

What changed?

Thanks,
Dan

I've had one tester with a dead battery scare me a bit when it didn't indicate on a live circuit. Since I always double-check on a known live circuit everything was safe for me. However, I kept thinking about the average user who won't check to make sure it beeps on something. They'll just go diving in with a tester that has a dead battery and possibly get hurt or killed.

Of course, if you're NOT average and understand the risks and how to double-check your gear, then this is a great tester. But I'm getting more cautious as I teach consumers how to use a NCVT to detect hot-wire and hot-skin conditions on their RV.
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Tim Perry

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Re: freak accident? help!
« Reply #175 on: September 04, 2013, 11:06:23 pm »

I've had one tester with a dead battery scare me a bit when it didn't indicate on a live circuit. Since I always double-check on a known live circuit everything was safe for me. However, I kept thinking about the average user who won't check to make sure it beeps on something. They'll just go diving in with a tester that has a dead battery and possibly get hurt or killed.

Of course, if you're NOT average and understand the risks and how to double-check your gear, then this is a great tester. But I'm getting more cautious as I teach consumers how to use a NCVT to detect hot-wire and hot-skin conditions on their RV.

If you are above average you may buy the more expensive lithium batteries that last 12 times longer for this application.
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Nathan Vanderslice

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Re: freak accident? help!
« Reply #176 on: September 05, 2013, 01:58:52 am »

My wife had Dobermans when she was growing up. One would eat ANYTHING, such as a hamburger right out the hot frying pan on the stove, or a beret from her school band uniform, and a Timex watch right off the dresser. The beret and watch made it through the doggie recycling process, but the beret was never the same, and the Timex didn't "keep on ticking" since the crystal broke on a tooth while the dog was chomping it down. They were planning to send the watch into the Timex "Keeps On Ticking" television ad campaign at the time, but it was not to be...

Perhaps someday you'll find your Fluke tester in a hole somewhere. If so, you should see if it still works and offer to send it to Fluke for a replacement. I'll bet they'll send you a new one in trade just for fun.

Mike Sokol

This reminds me of a story I heard years ago when an event was happening at an estate. Long story short, the day of load out, they backed the truck up that was picking up the piano. Bear in mind that this was a stage built on a slope. Well they had gotten the truck in position so that the truck bed and stage lined up. By this time there was a torrential downpour. Somehow the crew moving the piano completely missed the truck and the piano went off the stage to the low side of the hill and into the mud. It was taken back to the company, and they were so impressed at how well it held together, all they charged them for was the broken ivory on one of the keys.
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Mike Sokol

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Re: freak accident? help!
« Reply #177 on: September 05, 2013, 06:34:25 am »

If you are above average you may buy the more expensive lithium batteries that last 12 times longer for this application.

Hey, it had the cheap OEM batteries in it from the factory. But yes, that's why you buy the best batteries possible.  ;)

More than 30 years ago I had a voltmeter with cheap test leads, and one of the plugs fell out while I testing a power supply. Of course, the supply appeared to be "off" when it was indeed "hot".  But as I was reaching my hand into the supply I noticed the test lead plug laying beside the meter. I stopped quickly enough, since reaching a bare hand into a live high-voltage supply is a bad idea. After that I bought the best meter leads and meters I could get. I still remember this incident like it was yesterday. This electrical stuff can kill you if you're not careful.
« Last Edit: September 05, 2013, 07:34:09 am by Mike Sokol »
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Dan Mortensen

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Re: freak accident? help!
« Reply #178 on: September 08, 2013, 02:42:56 am »

Thanks to this thread, I got one of the Fluke probes and also the Amprobe one.

The buzzing of the Amprobe is nice, but it reacts the same to 120v and to whatever power is on a USB cable. It even reacts the same to the face of an iPad 1. It also doesn't necssarily react the same way to the same stimulus each time.

The Fluke, OTOH, has but a single beep at the lower voltage rather than a continuous tone, and behaves consistently.

Yes, I read Mike's response to Mark about odd behavior, but the two respond differently to the same stimulus and I like the Fluke's action better.

Also, I got one of the Amprobe INSP-3's, and it pops all the GFCI's in my kitchen when plugging in. (They are all the same make/model/vintage.) That's without activating the GFCI mode. Will test on three other GFCI make/model/vintages before saying anything more. Interesting data on non-GFCI's, though.

Thanks again for publicizing this, Mike.

Dan

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Mark McFarlane

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Re: freak accident? help!
« Reply #179 on: September 08, 2013, 09:54:05 am »

Thanks to this thread, I got one of the Fluke probes and also the Amprobe one....

Fluke alone sells 5 or more models. Which one did you get?
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Mark McFarlane
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Re: freak accident? help!
« Reply #179 on: September 08, 2013, 09:54:05 am »


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