Sharing some electric shock experiences

[gkmaia]

Yesterday I had my first mains electric shock... I got to tell you it was quite an experience. I felt like I had 10 red bulls in a row.

I was troubleshooting an old CRT scope and accidentally touched one of the CRT leads. Yes... I know, stupid, retarded, ignorant, could have died, etc...

Well, I got the DUT on an isolation transformer and my whole bench, including the transformer on an RCD. Interestingly every other time shorts happened the RCD reacted instantly... but yesterday it did not... sucker... also was the first time I used the DUT under my newly bought isolation transformer.

I have two questions to ask.

First, why my RCD did not shut off. My isolation transformer does not have a ground on the output. Is that the reason? The RCD could not detect the leakage thorough ground? Or actually the CRT & caps had enough energy stored to do not send a drop to the RCD?

Second, I would like to hear some shock experiences from other members. What happened and what you have done to avoid and make things safer.

I honestly feel so stupid... such a silly mistake, anyway.

[tautech]

Similar experiences:
https://www.eevblog.com/forum/chat/tell-us-about-a-time-you-got-electrocuted/

Once you place an isolation transformer in the bench an RCD is isolated from downstream of that.
It's output should be considered and Live + Live but only in respect to one another and they bare no relationship to mains ground/earth.

Play safe. 

[IanB]

First, why my RCD did not shut off. My isolation transformer does not have a ground on the output. Is that the reason? The RCD could not detect the leakage thorough ground? Or actually the CRT & caps had enough energy stored to do not send a drop to the RCD?

An isolation transformer isolates an RCD and renders it inoperative. You can isolate, or use an RCD, but not both at the same time.

Also, bear in mind that neither an RCD nor an isolation tranformer renders you safe from shock or electrocution. The only true safeguard is to apply safe working practices and not come into contact with high voltages in the first place.

Second, I would like to hear some shock experiences from other members. What happened and what you have done to avoid and make things safer.

Get shocked. It hurts! Try very hard to avoid shock in future.

(Joke mode ON) You should remove all safety devices from your lab and put up a big sign: "DANGER! Make one wrong move and you are dead!" Then read that sign before starting work and read it again every minute while working. (Joke mode OFF)

[magic]

Mains is a very different thing than an HV zap, you should try it once and stop confusing the two 
The telltale sign is that you can actually feel the frequency of it.

[Rerouter]

CRT's give you a right proper kick,

To actually have the RCD respond it would have to be after the isolation transformer

RCD's measure the difference in current on the active and the neutral, when its driving a transformer, nothing you do on the output causes a difference in that measurement,

If there was an RCD on the output of your isolation transformer, then there would be a mismatch in current (high voltage flowing through you out of the loop), and would trip,

Note that in all cases RCD's will not save you if you touch active and nuetral before you touch ground, This is why its not a bad Idea to have a easy to hit kill switch, In the past I used a foot switch to power up stuff under test depending on a switch on the back it either functioned as, If i pushed the foot switch, it latched off power, or only powered when i pushed it down, Again its those little idiot checks and understanding the safety devices you have in place that can keep you from biting it too hard

been tickled by 11KV mains once (Indirect, insulation crack on a buried wire into wet soil, and I touched a grounded fence), You have to shake the reapers hand off your shoulder after that.

[vk6zgo]

Yesterday I had my first mains electric shock... I got to tell you it was quite an experience. I felt like I had 10 red bulls in a row.

I was troubleshooting an old CRT scope and accidentally touched one of the CRT leads. Yes... I know, stupid, retarded, ignorant, could have died, etc...

Well, I got the DUT on an isolation transformer and my whole bench, including the transformer on an RCD. Interestingly every other time shorts happened the RCD reacted instantly... but yesterday it did not... sucker... also was the first time I used the DUT under my newly bought isolation transformer.

I have two questions to ask.

First, why my RCD did not shut off. My isolation transformer does not have a ground on the output. Is that the reason? The RCD could not detect the leakage thorough ground? Or actually the CRT & caps had enough energy stored to do not send a drop to the RCD?

Second, I would like to hear some shock experiences from other members. What happened and what you have done to avoid and make things safer.

I honestly feel so stupid... such a silly mistake, anyway.

The voltage you touched was probably from a power supply which was isolated from the Mains.(either a transformer type supply, a SMPS, or a RF type of HV supply.)
CRTs have other "high-ish" voltages to drive accelerating electrodes, quite apart from the "EHT" supply.

The RCD would have no way of tripping, even if you weren't using an external isolation transformer, because, in the Mains circuitry there was no unbalance between the current  in the L & N conductors.

In summary, you didn't get a Mains shock---- you got across one of the internal DC supplies.

Also, an isolation transformer & a RCD don't work like "belts & braces" ----the isolation transformer isolates the RCD, too!

[BradC]

Yes... I know, stupid, retarded, ignorant, could have died, etc...

Noooooo. Let's call it a *valuable* lesson. Everyone else has addressed the *why* (aside from you did something dumb). A *lot* of us have been there. Some of the dumber ones, like me, many more times than once.

I'm told I was 3 the first time I did the "funky dance". 440V bore contactor apparently. My dad had only wired up the "core balance relay" (now called an RCD) about 20 minutes prior and it was all sitting exposed on the bench. I'm told I did about 400 miles an hour backwards out of the shed.

I'm now 44 and I did it again last year by putting my thumb across the primary cap of an electronic fluoro ballast. It was disconnected, but still held ~300V. Welcome to the "club you don't really want to become a member of".

My kids (2 & 4) learned a valuable lesson on "watching daddy do something dumb".

[HalFET]

Don't forget getting shocked by the inductive kickback of a transformer when you unplug a power lead. That one has always been a fun one to get the blood flowing. 

[DDunfield]

Yesterday I had my first mains electric shock... I got to tell you it was quite an experience. I felt like I had 10 red bulls in a row.

I was troubleshooting an old CRT scope and accidentally touched one of the CRT leads. Yes... I know, stupid, retarded, ignorant, could have died, etc...

Well, I got the DUT on an isolation transformer and my whole bench, including the transformer on an RCD. Interestingly every other time shorts happened the RCD reacted instantly... but yesterday it did not... sucker... also was the first time I used the DUT under my newly bought isolation transformer.

I have two questions to ask.

First, why my RCD did not shut off. My isolation transformer does not have a ground on the output. Is that the reason? The RCD could not detect the leakage thorough ground? Or actually the CRT & caps had enough energy stored to do not send a drop to the RCD?

Second, I would like to hear some shock experiences from other members. What happened and what you have done to avoid and make things safer.

I honestly feel so stupid... such a silly mistake, anyway.

An RCD (called a GFI "Ground Fault Interrupter" here in Canada) works by detecting current flow to ground (ie: flow from the hot line that is not reflected in the neutral line).

Your isolation transformer can pump out into "whatever" but will always draw from the hot/neutral on the mains side, so the RCD sees a normal load.

Also, you mention "touched one of the CRT leads" which presumably was powered by an internal power supply in the DUT, and it likely also represented a "normal" load back to the mains, so not having and isolation transformer may not have made a difference in this case.

In general count on an RCD to only work when the leakage is directly from the mains - anything in between may turn leakage to ground into a normal looking load.


Regarding "make things safer" - my main recommendation is don't trust *anything* to protect you (other than your brain, and I'm cautious about that!) - I don't mean not to use protective devices (definitely DO), but don't TRUST them. They can fail, conditions can exist that you don't understand which undermines their effectiveness (as above).

One of my pet peeves is people connecting DUT to isolation transformer so they can hook up ground lead of non-isolated test equipment and "be safe". What they may not understand is that they have not only de-isolated their DUT but grounded it at a point where it was never designed to be grounded - probably making all kinds of normally safe-to-touch things hot ... Kindof the exact opposite of "safe".


I've been "bitten" a number of times, I think the worst was when I grabbed on to a still-powered camera tube with my fingers nicely in contact with the HV terminal (3kv IIRC). Back in the day I had pretty low body resistance for some reason (*1), so in addition to 100 needles being suddenly and forcefully jabbed into my fingers, I heard the HV supply complaining loudly about the excessive load. No idea what it was actually putting out in that condition - didn't really want to repeat the test.

The most surprising/unexpected time was when I had been working very late .. alarm went off far too early next morning and I was too groggy to handle hitting the off button, so I decided to yank the mains plug which happened to be right beside my bed ... managed to get it part way out and then got one finger on each live prong while it was still connected. MUCH faster way to wake up!!! - but I don't recommend it.

*1: When I was a teenager, I could get a reading of <1k Ohms by holding meter leads in each hand. The other guys could barely budge the needle. I could get a mild shock from 12v. The guys would laugh when they saw me testing LEDs with a 12v supply and no wires. Now that I'm older (and fatter) I'm over 200k even with wet hands.

Dave

[ruggedscot]

Okay - isolation transformer will stop you getting a shock if you contact a phase, however electrical circuits are not as they are drawn.. you get spare inductance and capacitance between the conductors and earth, and the transformer etc, so although from the drawing you would think you wouldn't get a shock the reality is that you may get a current flow. Hence Im not a lover of isolating transformers as a means to protect, it can give a false sense of security.... However using an isolating transformer you can create separation between your test bench and the mains proper. This means that you wouldn't trip your main RCD etc with any issues on your test bench, however you wouldn't have RCD protection, even if put an RCD between your isolating transformer and work bench.

To make the system work you will need to connect the neutral of the secondary winding of the isolating transformer to earth before the RCD. What this does is then provides you with a separated electrical supply from the mains that has the same configuration as the mains supply but any earth faults generated on your bench wont travel back to the main board. This is often used on test benches where you are testing specific electrical items of equipment.

isolation transformers came about when there was no RCD available as a means to provide protection, however these days we have good protection even though they may trip from time to time.

[Red Squirrel]

Had shocks working on the telephone frame at work, sometimes get a little zing if the line your working on has a phone call come through. 

My favourite though has to be when I was working on a LCD and got a zing off the CFL driver.  First time I get a shock that actually leaves a mark on my skin.    Turns out ginger skin burning does not smell anything like a gingerbread man.   

Had plenty of 120v mains shocks too mostly as a kid as I used to always play with mains.

[Gyro]

My favourite though has to be when I was working on a LCD and got a zing off the CFL driver.  First time I get a shock that actually leaves a mark on my skin.    Turns out ginger skin burning does not smell anything like a gingerbread man.   

The higher the frequency the more the localised physical skin damage. You don't feel RF burns immediately but they tunnel deep and take a long time to heal.

[Red Squirrel]

My favourite though has to be when I was working on a LCD and got a zing off the CFL driver.  First time I get a shock that actually leaves a mark on my skin.    Turns out ginger skin burning does not smell anything like a gingerbread man.   

The higher the frequency the more the localised physical skin damage. You don't feel RF burns immediately but they tunnel deep and take a long time to heal.

Yeah this shock was probably more closer to a RF burn than a shock.  It was a high frequency transformer.

[Mortymore]

The higher the frequency the more the localised physical skin damage. You don't feel RF burns immediately but they tunnel deep and take a long time to heal.

That's because what they call "skin effect"? 

I had some 230v zaps but...
When I was 13... 14 year old connected a small wall-wart transformer (some 9vDC 500mA) and run a couple of meters of cable connected to it. Then I stripped the wires with my teeth.

[Howardlong]

Similar experiences:
https://www.eevblog.com/forum/chat/tell-us-about-a-time-you-got-electrocuted/

And eight pages of it here https://www.eevblog.com/forum/chat/electric-shock-experiences-for-those-still-alive/

[GlennSprigg]

Here in Aussie-Land we are supposed to have a "she'll be right!" attitude!. (Though not really!) 
Like most things in life, it just needs common sense, and knowing what you are doing. However...
I've had countless 100's of 'shocks', (mostly deliberately  ) in my 40+ years career !!

My skin resistance  is quite low, and I've regularly flicked the back of my fingers on a wire etc, while
I'm grounded, to see if it's Alive !! (240v here, not 110v). You never use the 'inside' of your finger or
hand, as the current contracts your muscles, as so you may grab it 'tighter' then !

I started my career with E.T.S.A. (the old main power authority in South-Aust). Almost without variance,
when working on/modifying circuitry/switchboard main control panels inside Sub-Stations, we would
have to work on such systems/panels while 'Live'  so as not to disrupt the local power-grid.
We would just stand on blocks of polystyrene to grab live terminals, studs, busbars etc to wire things up.
You just make sure you don't, for example, reach for a spanner etc from on top of the metal framing!! 

A couple of interesting point to think about though...

Voltages like 240v, CAN OF COURSE KILL YOU !  Mainly not just the number of mA through you, but the
amount of TIME it has been flowing. Even if you fall/thrown away say 2 secs later, what happens is that
your heart goes into what's called 'Ventricular-Fibrillation', which is a useless 'quivering' action of the heart.
You will need immediate CPR, and when finally available, the use of a 'Defibrillator' to normalize the heart.

HOWEVER, higher-voltage shocks are a different 'beast' all together !  (say... 4,000v, or 8,000v etc.).
(I'm not talking about 'Frequency' here, as mentioned above, as that's a whole new discussion).
Even relatively short periods of 'time' while connected, can result now in actual physical 'burning', of not
only the Dermis, but deep muscular burns, including organs! depending on the 'path' of the current flow.
Yet, MORE PEOPLE SURVIVE THESE ! if the time has not been too long.  Why ?...
These higher voltages result in the heart initially contracting so tightly, that the heart usually does NOT
go into 'Ventricular-Fibrillation', so when the shock is removed, it goes back to normal, & you 'survive' 

[bsudbrink]

When I was in high school (a very long time ago), a couple of friends and I were lab assistants for the freshman chemistry and physics classes.  Sometimes, there was nothing much to do and we were allowed (within reason) to mess around with the equipment.  Mostly it was things like the wave tank, multi-arm pendulums, the air track, hand cranked generators, gyroscopes, harmless stuff.  Once though, we found an old Ford Model T trembler coil back in the equipment room, still working.  I don't know how much voltage/current it generated (I seem to recall that we were feeding it 24V DC) but it was generating enough voltage to drive a small Jacob's ladder.  I was adjusting the "antenna" of the Jacob's ladder with a pair of pliers. I was smart enough to be using a pair with insulated handles but, at some point, the path of least resistance became through the pliers to the edge of the insulation, through the air to my index finger, through my hand to the heel of my hand and through the air to the terminal of the trembler coil.  Hurt like HE**!  My hand was "pins-and-needles" for the following day.

[voltsandjolts]

Adding to an old thread here with another story which might remind us to think safety first.

On 24 November 2020, Darren Harris was electrocuted in an abandoned building in Wolverhampton, while attempting to steal scrap metal.
"Unfortunately, I put my left arm into an 11KV switchboard, which completely melted my forearms down to the bone. "

Warning: some readers may find images of trauma contained within this article upsetting

Man's arms 'exploded' after 11,000-volt shock

[nctnico]

He is lucky. Many years ago I was told a story where an electrician vapourised completely in such an environment right in front of his co-worker.

I have had a couple of shocks over the years but typically once per decade.

[wobbly]

I was told a story where an electrician vapourised completely in such an environment right in front of his co-worker.

To completely vaporise an entire adult human being in an instant would be the same as boiling perhaps 50 Kg of water into super-heated steam in a similar time-frame.  If that takes even one whole second, then it would be a gigantic explosion!  Devastation would follow.  No co-workers would be around to tell the story.   

[EPAIII]

OK, I have been around for a long time. And have definitely been there and done that! And, of course I definitely knew better. But I got careless for one second. The result was 35,000 to 40,000 Volt DC passing from my hand to the bottom of my foot that was resting on a metal foot rest on the workbench. On my hand it went through a standard meter probe, that's THROUGH IT'S INSULATOR. And at my foot through my sock and shoe: IIRC a leather sole. I know exactly where because I found the burn marks on both.

That is the worst of only a very few shocks that I have received in over 65 years working with electrical and electronic items. In most other situations, often on a daily basis, I have avoided shocks with a knowledge and understanding of what I was working with and what the real dangers actually were. And what the actual precautions to prevent being shocked were.

So on to the OP's event. As others have correctly stated, the OP's shock was not from the "mains". An isolation transformer was in use and the shock did not come from the "mains" side of that transformer. Hopefully the isolation transformer in use was fully insulated on it's primary side.

CRT TVs, like most electronic equipment operate with DC Voltages, not AC as in the "mains". So the secondary side of that isolation transformer then went to the power supply or supplies that converted that AC to the several DC Voltages used in the circuit other than the HV used by the CRT itself. Two variations may exist at this stage. In older designs a two pin, non polarized plug was used on the line cord. And one side of the AC, "mains" was connected to the chassis. It was assumed that the chassis was fully enclose inside an insulating enclosure (wood, plastic, etc.) so the 50/50 chance of it being directly connected to the HOT side of the "mains) was OK. Later equipment had polarized plugs on the line cord and/or did not connect one side of the "mains" to the chassis. These potentially hot chassis were the PRIMARY reason why service personnel started using isolation transformers. Note below.

These DC supplies will have had a (or several) transformer with secondaries that provide several AC Voltages that are then rectified and filtered into the DC Voltages needed. Those DC Voltages are referenced to the chassis which is the DC ground. So, in some TVs the chassis was both the AC and DC ground, BUT it was NOT actually connected to an earth ground. That is a very important point.

Finally in the TV sets there was a need for an actual high Voltage to operate the CRT. That is what accelerated the electrons and made them fly from the filament to the screen's coating. This actual HV was generated by another transformer called the fly-back transformer. It's primary winding was part of the circuit that generated the horizontal sweep signal which was 17,750 Hz for B&W TV and 17,735 Hz for Color. This horizontal sweep signal had to ramp up in a linear fashion for most of each cycle and then rapidly return in a short time. The waveform was like saw teeth. The secondary produced the HV which was rectified and used in the CRT between the filament(s) and the screen coating. Notice that since the screen coating is usually close to actual ground potential, the filament(s) are at the elevated HV, one filament lead a few Volts higher than the other. So checking the filament Voltage on a CRT necessarily involved high Voltages and HV precautions. Many VOMs, both now and back when I was shocked, are not built for that. And that's what I forgot.

In the present case of our OP, the point he was shocked by is very likely either a filament lead or some other part of the electron gun at the rear of the CRT. The high DC Voltage there was isolated from the "mains" by at least two and probably three transformers: his isolation transformer, the initial DC supply transformer, and the fly-back transformer. And none of these transformers offered any protection what so ever against being shocked by that HV circuit. This is totally obvious once you understand that HV circuit. Oh, one more detail: the sides of the CRT are usually covered, inside and outside with conductive coatings. The inside coating is connected to the HV circuit via a connection on the side of the CRT while the outside coating is connected to the chassis via wires with springs to ensure good contact.

When the OP came in contact with that HV point he was also very likely also in contact with the chassis. The chassis being the "ground" point of the HV circuit provided the return path. This connection could have been a direct one with a body part actually touching the chassis or it could have been through another path that contained what are usually called insulators (like my incident). Something like his arm resting on a ground wire from a meter which was clamped on the chassis. Or many other possibilities.

Just because something is insulated does not mean it is insulated against an actual HV.

I hope this has not been too long. I hope beginners particularly will read all of it and try to understand.

Note: In my personal experience, stretching back to the 1950s, I have worked on equipment where the chassis was connected to one side of the "mains". I always found which pin on the line plug was so connected and I made absolutely sure the plug was inserted so that the chassis was NOT hot: trace the wire before connecting to the "mains" AND checking the chassis with a Volt meter to ground. I did this BEFORE touching anything when working on equipment, then and NOW. I did not use an isolation transformer back then and have only rarely used one in the years since.

More to the point, I do not like seeing the widespread use of isolation transformers today. Particularly their use by the rank novices in this hobby and field of work. These beginners hear of the dangers of shock and want to protect themselves. They hear of the protection that the isolation transformer actually does offer so they get one and use it. And then they STOP WORRYING about the actual dangers. They do not THINK THROUGH what they are doing and the actual dangers involved. They just assume that the isolation transformer, that they spent a bunch of their well earned $ $ $ on will protect them when, in fact it does have it's limitations. "A man’s got to know his limitations.", Clint Eastwood as Dirty Harry, 1973 movie Magnum Force.

In electronics you got to know and understand what you are working with. Many of the posts above tell me that not only the OP, but many of the responders do not know and understand how that TV set worked.

In my humble opinion, things like the isolation transformer are for the experienced worker who does understand things, not for the novice. The novice should FIRST obtain that understanding BEFORE starting to work on such things. And don't put that statement down. It is PRECISELY how I did things when I was just learning electricity and electronics and for the most part it has served me VERY WELL. That includes situations that were much more dangerous and life threatening than that TV monitor with a limited current capability, that did shock me. Some of those other situations were dangerous enough to include another absolute rule: NEVER WORK ALONE. ALWAYS HAVE A SECOND, SAFETY MAN PRESENT.

[twospoons]

I've been hit by 230VAC, but that was just a tickle compared to getting 25J arm to arm from a 900VDC capacitor bank in a prototype electric fence energiser. That one burnt holes in my fingers and left me shaking for half an hour afterwards.
Basically I got careless and forgot that capacitors can remain charged for a long time. Once I recovered from the shock, the first thing I did was solder a neon and a resistor across the capacitors to act as both bleed and danger warning.

[Phil1977]

It´s long ago but I clearly remember the situation in a larger test lab. I DIYed myself a small HV cascade to produce up to 2.5kV from mains. I used it with a variac to test insulations and see what happens with different capacitors while overcharging.

During these tests nothing bad happened. But once I wanted to modify the cascade circuit and obviously didn't discharge all capacitors (it´s a stupid quality of cascade circuits: if you discharge one cap, you recharge others. You have to discharge them in a strict order or all together to be safe.) I started soldering on it with metal tweezers and an ESD-protected iron. I think I don't need to say more than that the tweezers flew more 10m through the room because the shock went through the arms and muscles contracted the right way.

The next best memorable event was a small but hurting charged flash capacitor.

And once, also very long ago I somehow managed to open the cover of a NiCd-charger that was based on a capacitive dropper without tripping it´s interlock. First it was only slightly tingling but changing the batteries I got in touch with both sides of the open circuit. That really did hurt too.

[Sal Ammoniac]

My one (and only) electric shock happened when I was three years old and stuck a butter knife into an electric outlet. I guess I learned my lesson.

[globoy]

My one (and only) electric shock happened when I was three years old and stuck a butter knife into an electric outlet. I guess I learned my lesson.

That was my age at introduction to electricity via a shock too.  My mom threw away a bad extension cord.  I dug it out of the trash and plugged it in.  The frayed end was the plug...   She said she heard a big bang, ran into the kitchen to find me sitting on the floor with a shocked look [pun intended] on my face, my hand blackened and a cloud of smoke rising in the air.  Probably, I think, I mostly got a slight burn from the arc.  But she said I was hooked on all things electric after that.  So I credit my entire career and hobbies to that shock.