lethal voltages.

[tggzzz]

By and large, people that work with high voltage stuff for a living are very cautious, but that is different from the rather overwrought approach somewhat prevalent on this forum.

Counter-conclusion: if they had been as careless/ignorant as many posts on this forum indicate, there would have been deaths.

Analogy: running out into the road without looking isn't necessarily lethal, but it does significantly increase the probability of becoming a KSI statistic.
Similarly, lack of KSI amongst those that look first doesn't imply there are no problems associated with not looking.

We teach our kids how to avoid dangers they are too young to recognise. We should teach newbies how to avoid dangers they don't realise exist.

[mcovington]

I was once working as the electrical engineer at a plywood plant in Fiji. When they ordered a new DC drive for a veneer lathe, a young Aussie electrician from ABB came to install it. This guy nearly died while working on the panel as he forgot to turn off the 3 phase/440volt breaker on the other side of the room before trying to loosen one of the feeder cables coming in to the panel. When I got there, he was crouched on the floor unconscious and his palm around the cable where it was insulated. By some miracle his hand slipped down enough for him to be alive. I nearly touched him unknowingly but something told me he did not look good. My immediate reaction was to throw the isolator off before calling the mill workers to carry him down from the room to a car. He was off to the hospital rigid like a pole, his legs protruding from the open windows. He had burn marks on his hand and on his calf where it had made contact with the frame of the panel. After a few days in the hospital he was gone and another guy had to come and finish the project. (A-hole never thanked me!)
As I write this, I am shivering thinking how close it was for me!

Poor fellow.  I wonder in what condition he survived.  He might have had brain damage.  Do you know whether he recovered to lead a normal life?

[mcovington]

So we have accounts of fatalities from the AC line and probably from power-supply outputs in the over-100-volt range that can deliver tens of mA or more.

None, so far, from CRTs; despite the higher voltage; the current is lower.

Of course, I do not want anyone to experience an electric shock.  One thing my doctor told me a while back is that after any non-trivial electric shock, there can be aftereffects on the heart due to the body's chemical response, and you should go to the emergency room even if you seem to be OK.

[0culus]

The account says he was gone, so I assume he did not survive? Odd choice of language though, as above it says he nearly died? 


I think another factor is that truly high amperage hazards (utility side of your electric, industrial electric service, electric railroads, etc) are usually also arc flash hazards...and arc flash will definitely mess you up, and often is fatal blow in those situations, as it were.

[james_s]

A friend of mine worked in an old building about 10 years ago and an electrician who came out to service something was electrocuted and died on the spot. Again not CRT related but line voltage, either 208 or 480V 3 phase I'm not sure.

As I said earlier, I think it's highly unlikely for the EHT in a CRT device to kill a person, but there are "low" voltages that are still sufficiently high to be dangerous and can deliver a lot of current if one does not know what they're doing.

[0culus]

Yeah. A service like that will easily deal more than enough fatal current before the circuit breaker or fuse is even breaking a sweat. Hence, GFCI and arc fault breakers standard in household wiring. On the industrial or utility side of things...there's no fuse and the system will happily deliver massive current to ground through you with no problems and create arc flash situations.

[mengfei]

I had an ARC jump on me from an Old CRT TV I was repairing.

I was reaching for a wire at the back of the Flyback X-former close to the anode cap, as I was reaching in & about an inch or two from the anode cap an ARC jumping out of the wire, could have had a crack, close to the cap hit my wrist which I slammed to the side of the tv case. There was a slight burn but the pain was from the slamming 

So I "guess" although that pumps out around 25KV+ the current is very very small to make your heart stop.
 

[andy3055]

I was once working as the electrical engineer at a plywood plant in Fiji. When they ordered a new DC drive for a veneer lathe, a young Aussie electrician from ABB came to install it. This guy nearly died while working on the panel as he forgot to turn off the 3 phase/440volt breaker on the other side of the room before trying to loosen one of the feeder cables coming in to the panel. When I got there, he was crouched on the floor unconscious and his palm around the cable where it was insulated. By some miracle his hand slipped down enough for him to be alive. I nearly touched him unknowingly but something told me he did not look good. My immediate reaction was to throw the isolator off before calling the mill workers to carry him down from the room to a car. He was off to the hospital rigid like a pole, his legs protruding from the open windows. He had burn marks on his hand and on his calf where it had made contact with the frame of the panel. After a few days in the hospital he was gone and another guy had to come and finish the project. (A-hole never thanked me!)
As I write this, I am shivering thinking how close it was for me!

Poor fellow.  I wonder in what condition he survived.  He might have had brain damage.  Do you know whether he recovered to lead a normal life?

Never heard from him after that. He went back to Australia and the other guy came to complete the work. Just before he left, he came on site to pick up his stuff. I bet he recovered well. If I remember he was in his early 20s. Skinny fellow!

[shakalnokturn]

Beware of bulk capacitors in SMPS charged to 300-400V they store enough energy to shake you for seconds.
The capacitor known to be a "frequent" killer is the one in microwave ovens when the bleeder resistor goes open.

Although not as tricky as ground referenced AC, that most people beware of when they actually understand the risk, capacitors or secondary side DC have no RCD/GFCI.

As mentioned before the risk after a severe enough DC shock is aftermath "poisoning" from electrolysis.

[dom0]

So we have accounts of fatalities from the AC line and probably from power-supply outputs in the over-100-volt range that can deliver tens of mA or more.

None, so far, from CRTs; despite the higher voltage; the current is lower.

Energy is much lower, too. The output caps of a HV multiplier may hold something like 20-30 mJ, meanwhile a good sized SMPS input capacitor will hold several Joules. Discharging the anode lead is supposed to produce a "zap", meanwhile, if you short the input caps on a higher power (100+ W) SMPS, which is not recommended, it will produce a real BANG.

[james_s]

One of the Electrohome monitors that was very common in arcade games of the early 80s has a second fuse after the bulk filter capacitor. When the flyback or HOT fails it will normally blow this fuse leaving the capacitor fully charged. I have been bit a couple times by one of those, even though it's "only" 170V it packs an enormous punch.

[vk6zgo]

One of the Electrohome monitors that was very common in arcade games of the early 80s has a second fuse after the bulk filter capacitor. When the flyback or HOT fails it will normally blow this fuse leaving the capacitor fully charged. I have been bit a couple times by one of those, even though it's "only" 170V it packs an enormous punch.

Electrohome design is to say the least, idiosyncratic!

Back in the day, I discovered another way to get "zapped", when digging round in the guts of a washing  machine.
This machine had quite a large oil filled capacitor connected across the Mains during use.----I am vague about its purpose, it was many years ago.

I turned the washer off, unplugged it from the ac  Mains, & delved confidently inside.

Anti-intuitively, I "copped" a nice shock.

It turns out that mechanical switches are quite fast compared to the 20ms occupied by the 50Hz cycle, so the power can easily be cut off part way through a cycle, charging the cap to whatever polarity & amplitude the cycle is in at that instant.

"Sod's Law" decrees that it won't be at a zero crossing!

I knew special relays could be very fast--- changing the RF drive on the old Marconi TV transmitters only caused the loss of a few lines on the transmitted picture, but I always thought ordinary switches were fairly leisurely in action!

[james_s]

Despite a few oddities in the design, the Electrohome G07 is a dependable monitor that is easy to work on and makes a good picture when they are dialed in. I have a few of them in games and while I've had to replace most of the original flybacks (LOPT) I have not had any trouble again with any that I've fixed.

The only purpose I can think of for a large capacitor across the mains is power factor correction. Odd that it wouldn't have been right across the motor though in which case the motor windings would quickly discharge it.

[mengfei]

...Oh & one of the small lethal device that could give you a BIG shock are those E-caps around camera flash! those have a rating of 400 Volts!

[EHT]

..there are "low" voltages that are still sufficiently high to be dangerous and can deliver a lot of current if one does not know what they're doing.

So I have a related question - what is the lowest voltage which we should consider dangerous? Has anyone had a surprise shock from a circuit they though was low enough to be safe, but were wrong?

I think 50V is usually referred to so I tend to go by that. We know 110V is high enough to travel through anyone careless enough to touch it; what about 40-80V range? Supplies at this voltage are often pretty high current ...

[shakalnokturn]

I remember getting tingled, not a nasty shock, from VCR VFD supply.

The books I learnt my basics from stated the "safe" voltages at 50V DC and 24V AC if I remember correctly.

The "high current" source always makes me frown, it usually reveals a misunderstanding of the danger. The example I have heard the most is the car battery being dangerous due to the amount of current it can deliver, true, it is dangerous in some respect due to that. Yet I'm still waiting for someone to get electrocuted on a car battery...

The availability of current brings other risks, if 10mA is considered the safe limit before becoming a life hazard high current sources are much lower current than expected...

For most work I won't put my fingers in until I understand the equipment well enough, then when I do know the risks I'll go to the trouble of discharging capacitors that will add-up to more than 30V. That means most audio amplifiers are considered dangerous.

[vk6zgo]

I remember getting tingled, not a nasty shock, from VCR VFD supply.

The books I learnt my basics from stated the "safe" voltages at 50V DC and 24V AC if I remember correctly.

The "high current" source always makes me frown, it usually reveals a misunderstanding of the danger. The example I have heard the most is the car battery being dangerous due to the amount of current it can deliver, true, it is dangerous in some respect due to that. Yet I'm still waiting for someone to get electrocuted on a car battery...

Yes it seems that Ohm's Law is a new & startling concept to some people, including many who would be expected to understand it!

The availability of current brings other risks, if 10mA is considered the safe limit before becoming a life hazard high current sources are much lower current than expected...

For most work I won't put my fingers in until I understand the equipment well enough, then when I do know the risks I'll go to the trouble of discharging capacitors that will add-up to more than 30V. That means most audio amplifiers are considered dangerous.

[james_s]

I've never heard of anyone being electrocuted by a car battery but they can certainly be dangerous. My dad has a scar on his finger from a ring that got very hot almost instantly from a short between a wrench and car body.