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I would suspect their choice of floor wax and the material the cart's
wheels are made from. The equipment is all grounded, so you have to
generate the charge. There are floor waxes made to prevent this, and is
used in Electronics factories. Synthetic rubber and long life plastic
wheels generate static, so together they can cause this problem. Rubbing
two insulators together is the problem. There are ESD ground sraps for your
shoes to help bleed away sartic from your body.

On Sat, May 4, 2024 at 12:31?PM cheater cheater via groups.io
<cheater00social@...> wrote:

Hi all,
I frequent a large grocery market nearby and inevitably every time I
go there I get electrical shocks. I walk around with a cart and often
if I touch a metal fixture (fridge, mesh rack) I get a painful shock.
Sometimes I get a shock if I leave the cart for a few seconds and then
touch its metal mesh.

I was wondering what everyone thought. At first I thought it would be
ESD, but why would it be so extreme? It happens every time. I live in
a place that's pretty dry - RH goes under 20% regularly - and being on
a plain it has a lot of wind, which could create triboelectric
charging. But I'm not really sure about this.

I don't know which way the ESD happens. Is my body discharging into
the cart? Is the cart discharging into my body? Is my body discharging
into the racks or vice versa? How can one check the directionality of
ESD?

One theory about ESD I have is that the fixtures get charged and my
body gets the charge applied to it. This however isn't necessarily
true to me because eg today I got a painful shock from touching the
inside metal surface of a fridge, and that's supposed to be earthed.

Another theory is that as I walk around in the store, as I move around
with the cart, that charges my body. I wear rubber sandals and the
cart has rubber wheels. That would mean I'm a conductor, attached to a
large antenna (the cart's mesh frame), moving through dry air,
insulated from the ground. The ground is made out of some sort of high
impact ceramic-ish tile. But then why would my own cart shock me just
mere seconds after letting go of it? I was unloading my groceries for
the cashier.

My third theory is that this whole facility has a lifted earth
potential. There's an industrial area nearby and they may be dumping a
lot of current into earth which would create a situation where walking
on the ground charges you, and then touching something that's low-Z to
neutral discharges your body (in this case this would be the earthed
fridges etc).

I was wondering how people would approach diagnosing this problem, and
how you would fix it if you had the ability to change anything about
the facility at hand - more as a thought exercise, but if I figure out
what's going on I'm going to write to the company.

Thanks

A shopping cart that accumulates a static charge fits the Charged Device
Model (CDM). It doesn't really matter which direction or polarity the
charge represents from a perspective of being shocked. Unfortunately the
initial discharge pulse would probably blow open an LED with the several
amps of discharge current that occurs. The user and the shopping cart
represent several thousand picofarads of capacitance. And depending on the
type of dielectric material used in the cart wheels and the user's shoes,
the charge can reach many thousands of volts. And it's made worse with
waxed floors. About the only thing you can do is to touch the cart to a
grounded item like a freezer or refrigerator to discharge it and yourself.

In an electronics manufacturing facility we'd use special ESD floor tiles
and carts with drag chains to continuously discharge carts as they were
moved. The entrance to those areas had a sign on the tile floors clearly
saying NO WAX so the housekeeping folks wouldn't defeat the ESD dissipative
floor tiles with a wax coating. But when the carts were used in the common
hallways with non-ESD tiles and waxed floors to use the elevator, we had to
touch the cart to the frame of the elevator door to discharge us and the
cart before we pushed the elevator button.

In our lab, a coworker had sneakers that were really bad about building up
a triboelectric charge and he would draw a 6" to 8" long spark from his arm
or shoulder when he turned the corner (with a grounded wall) into his
cubicle. And that didn't involve a cart. But it clearly exceeded the energy
expected in the Human Body Model of ESD control.

I wrote a nice story earlier about experiments with LEDs as ESD indicators, but it disappeared, so here's a short summary, then I'm done.

The LED survived many HBM discharges at 27 kV, the highest I could get my ESD tester up to. The LED light was very poor though, just barely visible in the dark. Need to try high efficiency type LEDs. Also, the neon lamp suggestion someone suggested could be good alternative.

I will try some more experiments just for fun.

Ed

The ESD is a narrow pulse, so it is dim. A small capacitor across the LED
might help. You can also use a string of regular diodes to clamp the
pulse's voltage. They have to total more than the forward voltage of the
LED so a resistor can limit the pulse current to a safe range.

On Thu, May 9, 2024 at 9:14?PM Ed Breya via groups.io <edbreya=
[email protected]> wrote:

I wrote a nice story earlier about experiments with LEDs as ESD
indicators, but it disappeared, so here's a short summary, then I'm done.

The LED survived many HBM discharges at 27 kV, the highest I could get my
ESD tester up to. The LED light was very poor though, just barely visible
in the dark. Need to try high efficiency type LEDs. Also, the neon lamp
suggestion someone suggested could be good alternative.

I will try some more experiments just for fun.

Ed

Perhaps it has been mentioned in this thread and I missed it. Our local Walmart (upstate NY) add short pieces of stiff, apparently steel, wire (I'd guess around 18AWG) to the bottom of each shopping cart -- the wire dragging on the floor killed the charge. Worked very well--I was constantly being zapped before they made the mod.

I have not seen this in years though the devices are still in place. Some
anesthetics used in surgery are flammable. To prevent possible ignition
from static discharge, we used to have to wear shoe covers that had a
grounding strap that made contact with our ankles and then went under the
bottom of the cover to contact the floor. The device was a tester. You
stood on it with your shoe covers on and touched a plate. If you were
properly grounded, you would get an “OK” light or a meter needle would move
into the green zone.

Largely because the use of flammable anesthetics has decreased markedly
because of newer nonflammable anesthetics, we have not worn the grounding
shoe covers in years but the conductivity testers are still around (they
are built into the walls which is probably the reason they are still there).


On Thu, May 9, 2024 at 02:54 Michael A. Terrell via groups.io
<terrell.michael.a@...> wrote:

I would suspect their choice of floor wax and the material the cart's
wheels are made from. The equipment is all grounded, so you have to
generate the charge. There are floor waxes made to prevent this, and is
used in Electronics factories. Synthetic rubber and long life plastic
wheels generate static, so together they can cause this problem. Rubbing
two insulators together is the problem. There are ESD ground sraps for your
shoes to help bleed away sartic from your body.

On Sat, May 4, 2024 at 12:31?PM cheater cheater via groups.io
<cheater00social@...> wrote:

Hi all,
I frequent a large grocery market nearby and inevitably every time I
go there I get electrical shocks. I walk around with a cart and often
if I touch a metal fixture (fridge, mesh rack) I get a painful shock.
Sometimes I get a shock if I leave the cart for a few seconds and then
touch its metal mesh.

I was wondering what everyone thought. At first I thought it would be
ESD, but why would it be so extreme? It happens every time. I live in
a place that's pretty dry - RH goes under 20% regularly - and being on
a plain it has a lot of wind, which could create triboelectric
charging. But I'm not really sure about this.

I don't know which way the ESD happens. Is my body discharging into
the cart? Is the cart discharging into my body? Is my body discharging
into the racks or vice versa? How can one check the directionality of
ESD?

One theory about ESD I have is that the fixtures get charged and my
body gets the charge applied to it. This however isn't necessarily
true to me because eg today I got a painful shock from touching the
inside metal surface of a fridge, and that's supposed to be earthed.

Another theory is that as I walk around in the store, as I move around
with the cart, that charges my body. I wear rubber sandals and the
cart has rubber wheels. That would mean I'm a conductor, attached to a
large antenna (the cart's mesh frame), moving through dry air,
insulated from the ground. The ground is made out of some sort of high
impact ceramic-ish tile. But then why would my own cart shock me just
mere seconds after letting go of it? I was unloading my groceries for
the cashier.

My third theory is that this whole facility has a lifted earth
potential. There's an industrial area nearby and they may be dumping a
lot of current into earth which would create a situation where walking
on the ground charges you, and then touching something that's low-Z to
neutral discharges your body (in this case this would be the earthed
fridges etc).

I was wondering how people would approach diagnosing this problem, and
how you would fix it if you had the ability to change anything about
the facility at hand - more as a thought exercise, but if I figure out
what's going on I'm going to write to the company.

Thanks

Harvey I'll need a drawing of that, can you take a photo and post it
to the list? Or if that doesn't work, to imgur? Thanks

On Thu, May 9, 2024 at 6:10?AM Harvey White via groups.io
<madyn@...> wrote:

If you're looking for direction, you'll need two of them

I'd be tempted to use a resistor and neon with a one KV diode in series
with the neon. The neon will limit the maximum voltage to about 100
volts or so.

so: resistor connected to a neon with a series diode, connecting both
across each other, and the diodes reversed.

Might be a good idea.

Harvey


On 5/8/2024 11:00 PM, stevenhorii wrote:

Could you use a small (NE-2) neon bulb for this? I recall holding the lead
of one and shuffling across a carpet. I got the bulb to flash.

Steve H.

On Wed, May 8, 2024 at 21:03 Ed Breya via groups.io <edbreya=
[email protected]> wrote:

The LEDs would protect each other from reverse breakdown. They should be
stout enough to take the forward hit and flash. If not, you can put some C
across them or R in series to soften things up (which would also stretch
the pulse for better visibility). Try it and see.

What's really needed to assess part durability is a power rating and an
energy rating. You won't find energy rating for LEDs, so have to
experiment. If you study the HBM you'll have an idea of the energy
available from your own spark. Unfortunately, I don't think there's a spec
for SCM, but you can be sure it would be quite a bit more C, and nearly
zero R. Good luck.

Ed

Steven great idea but how would I get this to be directional? I know
that the discharge happens by the pain alone, so the next step is to
figure out which way it's going.

On Thu, May 9, 2024 at 5:00?AM stevenhorii via groups.io
<sonodocsch@...> wrote:

Could you use a small (NE-2) neon bulb for this? I recall holding the lead
of one and shuffling across a carpet. I got the bulb to flash.

Steve H.

On Wed, May 8, 2024 at 21:03 Ed Breya via groups.io <edbreya=
[email protected]> wrote:

The LEDs would protect each other from reverse breakdown. They should be
stout enough to take the forward hit and flash. If not, you can put some C
across them or R in series to soften things up (which would also stretch
the pulse for better visibility). Try it and see.

What's really needed to assess part durability is a power rating and an
energy rating. You won't find energy rating for LEDs, so have to
experiment. If you study the HBM you'll have an idea of the energy
available from your own spark. Unfortunately, I don't think there's a spec
for SCM, but you can be sure it would be quite a bit more C, and nearly
zero R. Good luck.

Ed

On 2024-05-10 10:31 AM, cheater cheater wrote:

Steven great idea but how would I get this to be directional? I know
that the discharge happens by the pain alone, so the next step is to
figure out which way it's going.

With a neon bulb you can see which electrode glows to determine polarity. I'd have to do some looking to determine which is which, but I recall that only one electrode glows on a neon bulb driven by DC. Not sure how long the flash would last and whether you could tell the difference by eye, though.

Steve Hendrix

Maybe colorizing the envelope with two different gels, or just colored
sharpies, could help. or put a divider right in the middle so light
doesn't bleed, and put the whole thing in a larger box where one half
is red and one half is blue (and they're divided by the said divider)

What voltage can a neon bulb withstand?

Are there compact neon bulbs that are still very long (say an inch+
while being very thin)?

On Fri, May 10, 2024 at 4:36?PM Steve Hendrix via groups.io
<SteveHx@...> wrote:

On 2024-05-10 10:31 AM, cheater cheater wrote:

Steven great idea but how would I get this to be directional? I know
that the discharge happens by the pain alone, so the next step is to
figure out which way it's going.

With a neon bulb you can see which electrode glows to determine
polarity. I'd have to do some looking to determine which is which, but I
recall that only one electrode glows on a neon bulb driven by DC. Not
sure how long the flash would last and whether you could tell the
difference by eye, though.

Steve Hendrix

Photo in the photo album, look under neons.

Harvey

great stuff, thanks Harvey. any idea what sort of neon lamps to get?
are there standard model numbers?

On Fri, May 10, 2024 at 5:05?PM Harvey White via groups.io
<madyn@...> wrote:

Photo in the photo album, look under neons.

Harvey


On 5/10/2024 10:30 AM, cheater cheater wrote:

Harvey I'll need a drawing of that, can you take a photo and post it
to the list? Or if that doesn't work, to imgur? Thanks

On Thu, May 9, 2024 at 6:10?AM Harvey White via groups.io
<madyn@...> wrote:

If you're looking for direction, you'll need two of them

I'd be tempted to use a resistor and neon with a one KV diode in series
with the neon. The neon will limit the maximum voltage to about 100
volts or so.

so: resistor connected to a neon with a series diode, connecting both
across each other, and the diodes reversed.

Might be a good idea.

Harvey


On 5/8/2024 11:00 PM, stevenhorii wrote:

Could you use a small (NE-2) neon bulb for this? I recall holding the lead
of one and shuffling across a carpet. I got the bulb to flash.

Steve H.

On Wed, May 8, 2024 at 21:03 Ed Breya via groups.io <edbreya=
[email protected]> wrote:

The LEDs would protect each other from reverse breakdown. They should be
stout enough to take the forward hit and flash. If not, you can put some C
across them or R in series to soften things up (which would also stretch
the pulse for better visibility). Try it and see.

What's really needed to assess part durability is a power rating and an
energy rating. You won't find energy rating for LEDs, so have to
experiment. If you study the HBM you'll have an idea of the energy
available from your own spark. Unfortunately, I don't think there's a spec
for SCM, but you can be sure it would be quite a bit more C, and nearly
zero R. Good luck.

Ed

NE2H for one, it's a high brightness one, then any green neon will work for the other.? You could, of course, simply use two of the same lamp and just label them.

This same kind of circuit, with different resistors, would work with LEDS, but I'm not sure about the current, since neons can light with less current, IIRC.

Harvey

Hello everyone,

I've been carrying out expert assessments in the various fields of EMC for 40 years, and in the early years I was able to use a MONROE 175 electrostatic voltmeter to measure how people became charged. In 95 to 98% of cases, they were negatively charged.

But if there's one subject we couldn't care less about, it's whether the discharge is positive or negative. It's only the value of the peak voltage at which the person is charged that counts and has a direct influence on the effect and pain felt. I read at one point that the current value of relative humidity measured was only 20%. With such a low value, it's totally normal to become charged as soon as the person makes the slightest movement.

F1EKU

On Sun, May 12, 2024 at 11:07?AM F1EKU via groups.io
<rfconsulting.fr@...> wrote:

Hello everyone,

I've been carrying out expert assessments in the various fields of EMC for 40 years, and in the early years I was able to use a MONROE 175 electrostatic voltmeter to measure how people became charged. In 95 to 98% of cases, they were negatively charged.

But if there's one subject we couldn't care less about, it's whether the discharge is positive or negative. It's only the value of the peak voltage at which the person is charged that counts and has a direct influence on the effect and pain felt. I read at one point that the current value of relative humidity measured was only 20%. With such a low value, it's totally normal to become charged as soon as the person makes the slightest movement.

F1EKU

Thank you very much for your perspective.

Regarding measuring the direction of discharge current, I thought it
would be useful for detecting whether it is myself that is charged, or
the cart, or the display racks. Do you think that approach would be
useful for figuring out the answer to that? Especially given a couple
neon tubes are cheaper than a Monroe 175 by some orders of magnitude.

Thank you!

The one who's going to charge the most is the one who's going to move the most while being the most insulated from the ground. If we analyze the different protagonists present:
A rack presenting the products for sale, which doesn't move at all. It can only be charged by someone or something touching it.
A cart that moves with 4 wheels that turn around an axis with 4 ball bearings. There is very little friction, so there will be very little charge from the cart.
A man who pushes the cart and/or abandons it from time to time. Depending on the type of shoe used, it's usually the man who charges more often, and who also has a higher capacitance (around 80 to 120 pF) than the cart. This means it can accumulate larger charges.

Women in high heels often charge even more than men. They often wear nylon clothing, which helps to explain the rapid accumulation of charges, but above all, for an equivalent quantity of charges, if wearing heels reduces the capacity in relation to the ground by a factor of 2, then the resulting charge voltage is multiplied by two!
Now, I don't think the accumulated energy is capable of lighting up a neon light. And even if it could, the discharge time is so short (10 to 20 ns) that it seems impossible to have time to see anything.

If we take the most violent discharge that a human can achieve, the energy accumulated at 20 kV in 100 pF represents 0.02 joules. The smallest neon light requires 0.3 mA at 90 V to light up, which represents 0.027 joules. So I remain extremely dubious as to whether we can achieve the desired result.

F1EKU

A neon bulb certainly lights up with static discharge. I did some experiments with my ESD tester with HBM probe, at 27 kV, so a pretty good amount of juice, with LEDs and neons. First, with some regular old red LEDs, then high efficiency ones, then a neon bulb like NE-2 size. The regular LED was disappointing in brightness, and could only be seen faintly in the dark, as I described in a post a few weeks ago. The LED survived many discharges, indicated by before and after testing on the curve tracer. I later tried a a couple of small high efficiency "white" LEDs, stripped out of one of those Harbor Freight flashlights they used to give out for free. These worked sort of enough to see in room light, but only if viewed head-on. I found an interesting thing when I did the "after" test - they would not light, and showed no current draw. I put them back to the sparks, and they lit again! Apparently the bond wires blew at some point, but the HV easily continued to arc through the charred tubes left behind. The LED dies survived, but the wires did not. I'm convinced that some much heavier high efficiency illumination type LEDs would be stout enough to take the discharges, efficient enough to get some decent light, and omni-directional enough to have decent viewing angles. Adding some kind of temporary energy storage/pulse-stretching should help too. The overall efficiency is terrible due to the short event and poor Z-match, but I think it could work acceptably, with the right stuff. Remember, the goal (I think) is to have a passive circuit do the job. All this would be trivial with an active circuit.

I did a quick look at a neon, and it flashed just enough to be visible in room light, and only a small part of the electrode lit up. It could be usable, but would need some pulse stretching too - it's a quite small, dim flash as-is. The bulb also started to glow as the probe approached the bulb wiring, due to corona discharge. I could get it to discharge the HBM probe gradually enough on approach, to skip most of the spark and have just a feeble sound and flash at the end. The LEDs would be subject to the corona discharge too, but the current and light output are so small it wouldn't be noticed. One way to get better results from neons light-wise, would be to have a whole bunch of bulbs in series, clustered together for size. If you say, put a dozen up, it would still glow on approach, but strike at around 1 kV if you move fast enough - a small amount compared to the maybe 8 kV and up charges involved.

Ed

On Wed, May 22, 2024 at 2:23?AM F1EKU via groups.io
<rfconsulting.fr@...> wrote:

The one who's going to charge the most is the one who's going to move the most while being the most insulated from the ground. If we analyze the different protagonists present:
A rack presenting the products for sale, which doesn't move at all. It can only be charged by someone or something touching it.
A cart that moves with 4 wheels that turn around an axis with 4 ball bearings. There is very little friction, so there will be very little charge from the cart.
A man who pushes the cart and/or abandons it from time to time. Depending on the type of shoe used, it's usually the man who charges more often, and who also has a higher capacitance (around 80 to 120 pF) than the cart. This means it can accumulate larger charges.

Women in high heels often charge even more than men. They often wear nylon clothing, which helps to explain the rapid accumulation of charges, but above all, for an equivalent quantity of charges, if wearing heels reduces the capacity in relation to the ground by a factor of 2, then the resulting charge voltage is multiplied by two!
Now, I don't think the accumulated energy is capable of lighting up a neon light. And even if it could, the discharge time is so short (10 to 20 ns) that it seems impossible to have time to see anything.

If we take the most violent discharge that a human can achieve, the energy accumulated at 20 kV in 100 pF represents 0.02 joules. The smallest neon light requires 0.3 mA at 90 V to light up, which represents 0.027 joules. So I remain extremely dubious as to whether we can achieve the desired result.

F1EKU

We're talking about a relatively large open-plan warehouse with a lot
of air circulation, large thermal gradients due to open refrigerating
shelves, and very tall, metal ceilings. I think the air is going to
create triboelectric charging in items that just stand around all day
long.

To quote Star Trek:

Scotty: What's that?
Spock Prime: Your equation for achieving transwarp beaming.
Scotty: [reads the equation] Imagine that! It never occurred to me to
think of SPACE as the thing that was moving!

Or in this situation... "air as the thing that was moving".

What do you think? Plausible?

27 kV is not 20 kV!

I took 20 kV because it's really the worst human load value I've measured in the 5 years I've had my MONROE Voltmeter. At the time (1985-1990), I had 4 electrostatic discharge simulators:
- Two from KEYTEK, the 3000 model up to 30 kV and the Minizap portable up to 15 kV.
- An old Schaffner 430 single polarity up to 25 kV (from memory) and a more modern 432 dual polarity with relay allowing contact discharges but limited to 16 kV.
After that, I had my hands on just about every make and model of simulator except NoiseKen. Last year I sold a Schaffner 435 and an EMC Partner ESD3000 16 kV, and earlier this year an EMC Partner 30 kV.

Today, I've only kept two devices: an old Schl?der 16 kV that I don't use at all any more, and "THE" Schaffner/Teseq 438, which is by far the best simulator ever made, and which I'll probably take to my grave!

In our case, the man doesn't discharge to earth, but to an ungrounded cart or rack.

So we get a partial discharge, a charge balancing between two capacities, which means that there will never be 20 or 27 kV, but only about ten kV, which is bad enough.

So please stop dreaming up laboratory tests that I can also do perfectly well, and try to think before you transpose what you do in the lab into field tests.
If you want to check that a neon light or a LED can be turned on in real conditions, redo all the tests with only about 10 kV and, above all, don't keep the current standardized value of 150 pF / 330 ohms, but take a more realistic value of 100 pF / 450 ohms, which corresponds to what an average human can represent.

Of course, we need only consider purely passive devices. Active devices do exist, but their price is too high to be discussed here. On the other hand, these passive devices need to work in real-life conditions, not in the laboratory. 27 kV never exists in real-life conditions, otherwise IEC 61000-4-2 would not have been content to define level 4 at 15 kV only.

150 pF / 330 ohms is a bit of a stretch to really allow maximalist testing according IEC 61000-4-2. If you verify in other standards you will see that some other HBM will be used.

F1EKU

I used 27 kV to get the most out that I could for the experiments - that's the highest my ESD tester can go. Of course that's not expected in real life, but to at least get some observations quickly with various parts. The point was to first see some light, then to figure out how to make it better, then figure out if it's practical for the application.

Ed