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[Mike Sokol]

I've sent in suggestions over the last year to the Rossen Report (an NBC news program) about testing lighting poles for stray voltage, so of course they ran this "report" today without any input from me on why this occurs or how to test for it yourself. Oh well. Here's the full video report. http://www.today.com/video/today/56416055/#56416055

Yeah, I've done this sparking trick in my own lab, but thought it was too theatrical for my NO~Shock~Zone seminars. What do you think, lower the lights and make a microphone spark with a grounded screwdriver?

[Brian Bolly]

WBAL TV in Baltimore ran a similar report a couple days ago with the same testing company/crew.

http://www.wbaltv.com/news/contact-voltage-inspections-protecting-public-questioned/29640832

[John Roberts {JR}]

Kind of like the way that MTV changed the music industry, TV news is all about the visuals. Read newspapers for facts, TV news for the pictures.

JR

PS: This is why politicians put so much effort into engineering Photo-ops and short sound bites. TV news has the attention span and IQ of a gnat.

[Mike Sokol]

WBAL TV in Baltimore ran a similar report a couple days ago with the same testing company/crew.

http://www.wbaltv.com/news/contact-voltage-inspections-protecting-public-questioned/29640832

This WBAL video is mostly a pissing match between a pair of testing companies over who gets the contract. Not too much useful information for consumers, but at least it raises consumer awareness.   

Interestingly, WBAL calls this "Contact Voltage", while the Rossen Report calls it "Stray Voltage", and the RV Industry calls it a "Hot-Skin Voltage". I call it a "Hot Chassis Voltage" for pro-sound gear shock hazards. I wonder if there's a single name/description that could be used for ALL shock situations.

[Tim McCulloch]

I wonder if there's a single name/description that could be used for ALL shock situations.

I nominate "This shit will kill you. Dead. Dead. Dead."

[Mike Sokol]

I nominate "This shit will kill you. Dead. Dead. Dead."

Maybe a LITTLE over the top, but I like it...   

[Chris Hindle]

Maybe a LITTLE over the top, but I like it...   

Truth hurts, don't it......

[John Roberts {JR}]

"Fault voltage", Leakage voltage,

JR

[Stephen Swaffer]

 UEOs-unintentionally energized objects if you want code speak.

Interesting that their source is a company that does surveys and the big take away is that  everyone ought to be doing surveys. I am curious what his ground reference was for the sidewalk?  Having 90 volts on it is not an accurate statement-if the pole has 120 volts to reference and sidewalk has 90, then touching the pole only puts you across 30 volts (no I won't be a test subject).

IMO, identifying the root cause, compiling meaningful data and making preventative adjustments (code changes?) is what needs to happen.  Its not like "we" don't know how to prevent these problems.

But if a public outcry creates a demand for their services, then their advertising worked.

[Mike Sokol]

IMO, identifying the root cause, compiling meaningful data and making preventative adjustments (code changes?) is what needs to happen.  Its not like "we" don't know how to prevent these problems. But if a public outcry creates a demand for their services, then their advertising worked.

My issue with the "sparking" demonstrations is that it suggests you'll actually see sparks when someone gets shocked. And that's simply not the case with the voltages we'll normally encounter in the home or even in pro-sound work. But if you watch any television shows with low voltage shocks (under 600 volts) the film directors love to create blue-sparking outlines around the point of contact, or even around the entire body of the victim.

I guess it's become an industry cliche', much like the prerequisite feedback "squeal" when anyone on camera walks up to a podium mic. That's so the viewers will know "This mic is on and I'm speaking to a large crowd through it".

[Jonathan Johnson]

Yeah, I've done this sparking trick in my own lab

Getting a big spark off of a wooden pole is quite the trick! Wonder how much their spark stick would light up if I rubbed it on the tires of my car? Or maybe my cat?

[Stephen Swaffer]

Anyone see any irony in a video reporting safety hazards, reporter stepping back because sparks are flying everywhere,etc., and no safety glasses in sight?  Hard hat and safety vest-but no glasses-have they ever worked with OSHA?  If those sparks are real, they are droplets of molten metal-as dangerous to your eyes as the electric current is to your heart.

[Lyle Williams]

A baby tesla coil is the trick if you are trying to sell people on the idea that something is unsafe....  Much more convincing than a NCVT.

[Mike Sokol]

A baby tesla coil is the trick if you are trying to sell people on the idea that something is unsafe....  Much more convincing than a NCVT.

I have one, but it throws 2 ft arcs so maybe that's a bit too much.

But seriously, for those who understand electricity the NCVT demonstration is pretty convincing. That's because a large surface such as a mixing console or RV with 120-volts on the chassis will make a standard sensitivity NCVT beep and light from up to 2 feet away. I've posted this before, but here's a video of me testing a 40 ft RV for a "hot-skin" voltage. When my cameraman was shooting this and it beeped from nearly 2 ft away, I heard him say "holy s__t" under his breath. He said his crew had experienced a shock from their production trailer a few months before, and now he understood what it was. 

http://www.youtube.com/watch?v=Y8h64X33aKg

[Lyle Williams]

I have no problems with the NCVT test, it just isn't what people want to see on TV. 

People expect hollywood visuals.  Sadly they also expect CPR to work every time.

[John Roberts {JR}]

I have no problems with the NCVT test, it just isn't what people want to see on TV. 

People expect hollywood visuals.  Sadly they also expect CPR to work every time.

You just need a fancy game show style readout for the NCVT... perhaps a computer screen that can be projected larger onto a screen with flashing red indicators for dangerous voltage when present.  Keep in mind you just need to look impressive on TV or an even smaller screen.

You can create striking visuals without the cliche sparks and flashes. The TV producers will be willing to play along because that is what drives their presentations.

JR

[Frank Koenig]

Here's me taking a NCVT to none other than The Man himself (he proved not to be "hot"). I should have been standing on an insulating mat, I suppose. I took the picture for that thread on electrical monuments some months ago but didn't know how to get pictures to stick on the forum at the time. Best to all. Happy Thanksgiving, etc. --Frank

[Mike Sokol]

Here's me taking a NCVT to none other than The Man himself (he proved not to be "hot").

Frank, that's great. Is that a Fluke VoltAlert or Klein NCVT-1, or maybe something else? They look pretty similar at that distance. I want to send the picture to my promotional contacts to rile them up a bit. 

[Frank Koenig]

Is that a Fluke VoltAlert or Klein NCVT-1

It's a Klein NCVT-2, dual range. The more sensitive  range (12 - 48 V nominal) tends to light up on just about anything conductive (and, I suppose, not solidly grounded) near AC power. High range works as advertised.

Please do use the picture. I can send you the full-res original to crop and downsample for your needs.

I need to go back and check out what they did with those two pieces of 3/4 in. sch. 40 PVC sticking up out of the plinth. Maybe he WILL be energized? -F

[Mike Sokol]

Here's me taking a NCVT to none other than The Man himself (he proved not to be "hot").

Slightly (yeah, maybe a lot) OT, but here's an interesting prediction.

"...it will be possible for a business man in New York to dictate instructions, and have them instantly appear in type at his office in London or elsewhere.  He will be able to call up, from his desk, and talk to any telephone subscriber on the globe, without any change whatever in the existing equipment.  An inexpensive instrument, not bigger than a watch, will enable its bearer to hear anywhere, on sea or land, music or song, the speech of a political leader, the address of an eminent man of science, or the sermon of an eloquent clergyman, delivered in some other place, however distant.  In the same manner any picture, character, drawing, or print can be transferred from one to another place.  Millions of such instruments can be operated from but one plant of this kind."

Nikola Tesla, in 1908 - on his never-finished wireless communication tower, AKA a modern-day cell tower

[Mike Sokol]

"Fault voltage", Leakage voltage,

JR

Seriously, the problem with calling this sort of thing a "leakage voltage" is that there's three distinct types of hot-chassis fails. One is indeed a high-impedance/low-current "leakage voltage" that's measurable whenever there's a disconected EGC. As I often demonstrate in my seminars, even an iPhone with a Apple wall charger develops between 40 and 80 volts on its chassis (depending on which way the charger is plugged into the receptacle). But the available "leakage current" is way below 1 mA, perhaps a few hundred micro-amps at most for a properly build and operating "wall wart". The same holds true for a properly operating guitar amp, even if its ground pin on the power cord is broken off. There may be a little fault current available, but typically not enough to be noticed.   

On the other hand, without an EGC to drain away any fault currents, you won't know when this turns into a mid-impedance (~1,000 ohms)/medium-current "leakage voltage". That's when there's 10 to 100 mA of ground fault current available. There's a pile of ways this can happen from an old, leaky "stinger cap" on a antique Fender amp, to an aging power transformer in your bass amp, or even a bunch of "leaky" gear plugged into the same power strip. Hey, even MOV based "surge strips" leak a small amount of current from hot-to-ground, so once you get around 5 to 10 mA of leakage to the chassis, then it gets VERY noticeable when touched with wet hands. And 20 mA through you is enough current to overcome your hand's opening muscles, which then causes you to clamp onto a hot mic or wire and not be able to let go. Just 30 mA though your chest cavity for more than a few seconds is almost a guarantee of ventricular fibrillation and death by electrocution if help doesn't arrive in time. Ouch. 

The final (and most dangerous of all) "leakage voltage" isn't really a leak at all. It's a hard, low-impedance fault with a hot-to-chassis short which can result from a wire pinched inside a chassis,  cut insulation on a power cord draped over a metal stair on a stage, or even RPBG miswiring in an "upgraded" outlet. Those are the conditions that can cause the OCP breaker to trip or make a mic wire to glow red and catch on fire, and will certainly draw sparks from a grounded screwdriver like the videos above. However, these hard faults are less common than the first two, but not unheard of.

The problem is that without additional testing you really can't determine if you have a low, mid or high-current hot-chassis voltage. But if a properly earth-bonded EGC is in place, then it's impossible for any of the above fault conditons to create a shock hazard. A low-current fault will be drained away without you ever knowing about it. A mid-current fault will likely cause your GFCI to trip for no apparent reason, but saving your life in the process. And a high-current fault may trip an OCP in your distro,  but can kill you in heartbeat (literally) if you get between it and a solid ground.

So my mantra is that your should NEVER feel a sustained shock. A one-time static jolt from walking on the carpet isn't the same thing. I'm talking about a tingle when touching your guitar or mixer or mic and a damp floor or grounded gear at the same time. Or ANY home appliance or power tool for that matter. If you feel a shock from your refrigerator at home while touching the stove or sink, then something has gone seriously wrong with your appliance ground and the next touch could kill you or someone you know/love. So don't let a shock situation exist for longer than it takes you to unplug it from AC power. Fix it NOW before it kills somebody (even you). 

[Jonathan Johnson]

Slightly (yeah, maybe a lot) OT, but here's an interesting prediction.

"...it will be possible for a business man in New York to dictate instructions, and have them instantly appear in type at his office in London or elsewhere.  He will be able to call up, from his desk, and talk to any telephone subscriber on the globe, without any change whatever in the existing equipment.  An inexpensive instrument, not bigger than a watch, will enable its bearer to hear anywhere, on sea or land, music or song, the speech of a political leader, the address of an eminent man of science, or the sermon of an eloquent clergyman, delivered in some other place, however distant.  In the same manner any picture, character, drawing, or print can be transferred from one to another place.  Millions of such instruments can be operated from but one plant of this kind."

Nikola Tesla, in 1908 - on his never-finished wireless communication tower, AKA a modern-day cell tower

In the 1940s, back when radios were still the size of iceboxes, my grandfather would tell people, "some day we will have radios you can fit in your shirt pocket" and they would laugh at him. He was just a farmer from the Dakota prairie, but he didn't let that limit his expectations of the world and its future.

(I never knew my grandfather; he died before I was born. My father told me that story.)

[Stephen Swaffer]

Seriously, the problem with calling this sort of thing a "leakage voltage" is that there's three distinct types of hot-chassis fails. One is indeed a high-impedance/low-current "leakage voltage" that's measurable whenever there's a disconected EGC. As I often demonstrate in my seminars, even an iPhone with a Apple wall charger develops between 40 and 80 volts on its chassis (depending on which way the charger is plugged into the receptacle). But the available "leakage current" is way below 1 mA, perhaps a few hundred micro-amps at most for a properly build and operating "wall wart". The same holds true for a properly operating guitar amp, even if its ground pin on the power cord is broken off. There may be a little fault current available, but typically not enough to be noticed.   

On the other hand, without an EGC to drain away any fault currents, you won't know when this turns into a mid-impedance (~1,000 ohms)/medium-current "leakage voltage". That's when there's 10 to 100 mA of ground fault current available. There's a pile of ways this can happen from an old, leaky "stinger cap" on a antique Fender amp, to an aging power transformer in your bass amp, or even a bunch of "leaky" gear plugged into the same power strip. Hey, even MOV based "surge strips" leak a small amount of current from hot-to-ground, so once you get around 5 to 10 mA of leakage to the chassis, then it gets VERY noticeable when touched with wet hands. And 20 mA through you is enough current to overcome your hand's opening muscles, which then causes you to clamp onto a hot mic or wire and not be able to let go. Just 30 mA though your chest cavity for more than a few seconds is almost a guarantee of ventricular fibrillation and death by electrocution if help doesn't arrive in time. Ouch. 

The final (and most dangerous of all) "leakage voltage" isn't really a leak at all. It's a hard, low-impedance fault with a hot-to-chassis short which can result from a wire pinched inside a chassis,  cut insulation on a power cord draped over a metal stair on a stage, or even RPBG miswiring in an "upgraded" outlet. Those are the conditions that can cause the OCP breaker to trip or make a mic wire to glow red and catch on fire, and will certainly draw sparks from a grounded screwdriver like the videos above. However, these hard faults are less common than the first two, but not unheard of.

The problem is that without additional testing you really can't determine if you have a low, mid or high-current hot-chassis voltage. But if a properly earth-bonded EGC is in place, then it's impossible for any of the above fault conditons to create a shock hazard. A low-current fault will be drained away without you ever knowing about it. A mid-current fault will likely cause your GFCI to trip for no apparent reason, but saving your life in the process. And a high-current fault may trip an OCP in your distro,  but can kill you in heartbeat (literally) if you get between it and a solid ground.

So my mantra is that your should NEVER feel a sustained shock. A one-time static jolt from walking on the carpet isn't the same thing. I'm talking about a tingle when touching your guitar or mixer or mic and a damp floor or grounded gear at the same time. Or ANY home appliance or power tool for that matter. If you feel a shock from your refrigerator at home while touching the stove or sink, then something has gone seriously wrong with your appliance ground and the next touch could kill you or someone you know/love. So don't let a shock situation exist for longer than it takes you to unplug it from AC power. Fix it NOW before it kills somebody (even you).

+1

The one thing I would add to this is to treat tripping GFCI with the same concern-don't just go find or install a non-GFCI receptacle to fix the problem.  The latest GFCIs should not reset if they are faulty-so more than likely if it keeps tripping the problem is with the attached appliance/equipment.  I just dealt with a situation where a year ago we had a tripping GFCI on a horse waterer at a stable.  I refused to remove  the GFCI and told them to fix the waterer.  Called me to look at it Saturday-a tenant "electrician" that works for a competitor replaced the GFCI with a standard duplex-and now it doesn't work again.  This time the heater is completely open-I guarantee you it was defective a year ago. Fortunately no person or animal got hurt-this time.

[ProSoundWeb Community]