Is electrocution possible from touching a conducting wire?

[genekuli]

TL;DR Summary

is electrocution possible from touching a good conductor (much lower resistance than the human) that is connecting terminals.
(electrocution) why would the current flow through a person when it is already flowing through a copper conductor that is connecting the terminals.
either in a capacitor or battery or AC.
is electrocution possible from touching a good conductor that is connecting terminals

why would the current flow through a person when it is already flowing through a copper conductor that is connecting the terminals.

 

[berkeman]

You get a shock when there is a voltage difference across different parts of your body. Can you rephrase your question? It takes more than one conducting path in contact with the body to cause a shock...

 

[genekuli]

i know the charge would flow into the person but would it flow through that person. practical eg.;
if i have a capacitor (with sufficient charge to electrocute),
i (eg, with one hand) hold a wire that is connecting the terminals,
at the time of discharge, why would the charge (that is flowing to the other terminal) flow through me to ground. if one touches either one of the charged terminals (independently) they will not flow to ground (even if i directly connect it to ground), so why would they flow to ground now through the person?

 

[berkeman]

i know the charge would flow into the person but would it flow through that person. practical eg.;
if i have a capacitor (with sufficient charge to electrocute),
i (eg, with one hand) hold a wire that is connecting the terminals,
at the time of discharge, why would the charge (that is flowing to the other terminal) flow through me to ground. if one touches either one of the charged terminals (independently) they will not flow to ground (even if i directly connect it to ground), so why would they flow to ground now through the person?

Sorry, I'm not able to parse your post at all. If you hold a charged capacitor in your hand and discharge it with your fingertip while holding a grounded wire, of course just your fingertip feels the shock. If the - terminal of the capacitor is grounded and you touch the + lead of the cap with one hand and grab a grounded wire with your other hand, you will get a hand-to-hand shock.

Are you familiar with why birds sitting on high voltage distribution wires do not get shocked?

https://pr-tech.com/blog/bird-deterrent-power-line-safety/

 

[Klystron]

While you rephrase your question as the moderator requests, I can reiterate safety guidelines common to laboratories, data centers and other work areas where electrocution remains a hazard. This list is not exhaustive:

1. Remove all jewelry, rings and watches before entering work areas. Even non-conducting objects such as wristbands can catch on hardware. Remove piercings including earrings.
2. Do not bring liquids into a lab. Keep clothing and safety shoes dry.
3. Tie back long hair. Tuck loose clothing. Secure lab coats, if worn. Cooling fans can suck in loose items potentially trapping you.
4. Wear proper non-conducting eye and ear protective devices as detailed in your lab protocols. Wear safety shoes both to prevent grounding yourself and to protect your feet from crush injuries.
5. Stay alert. Keep one hand in a pocket while near active electronics; usually the hand and arm on the side near your heart. Do not ground yourself or touch grounded items.
6. Never touch downed wires or fallen workers until power has been turned off.
7. Maintain situational awareness. Memorize escape routes. Locate exits, alarms, first aid kits and safety equipment.
8. Do not disable cabinet interlocks or other safety equipment.

With 50+ years experience I have seen and read first hand reports of terrible injuries. The worst electrocutions seem to happen to seasoned experienced workers who forgot a safety rule or made a simple mistake such as wearing a watch or prized jewelry. To this day I eschew wearing jewelry and always keep one hand in my pocket working in hazardous environments. Stay alert. Remain safe.

 

[anorlunda]

That person touched a wire with his hand.

 

[sysprog]

Looks like he completed the circuit with his footwear, which presumably provided life-saving resistance.

 

[genekuli]

if i can then simplify it to a simple battery circuit;
a battery circuit with a conductor between terminals,
another conductor branching off of the said conductor to the ground
would there be significant current in that ground connection conductor?
i don't think so, right?

 

[sysprog]

if i can then simplify it to a simple battery circuit;
a battery circuit with a conductor between terminals,
another conductor branching off of the said conductor to the ground
would there be significant current in that ground connection conductor?
i don't think so, right?

How much current flows to the ground depends on the characteristics of the ground connection $-$ especially on moist versus dry ground, but if you mean a short across the terminals, then no, you wouldn't get any significant parallel circuit with the 'to-the-ground' connection.

 

[DaveE]

While you rephrase your question as the moderator requests, I can reiterate safety guidelines common to laboratories, data centers and other work areas where electrocution remains a hazard. This list is not exhaustive:

1. Remove all jewelry, rings and watches before entering work areas. Even non-conducting objects such as wristbands can catch on hardware. Remove piercings including earrings.
2. Do not bring liquids into a lab. Keep clothing and safety shoes dry.
3. Tie back long hair. Tuck loose clothing. Secure lab coats, if worn. Cooling fans can suck in loose items potentially trapping you.
4. Wear proper non-conducting eye and ear protective devices as detailed in your lab protocols. Wear safety shoes both to prevent grounding yourself and to protect your feet from crush injuries.
5. Stay alert. Keep one hand in a pocket while near active electronics; usually the hand and arm on the side near your heart. Do not ground yourself or touch grounded items.
6. Never touch downed wires or fallen workers until power has been turned off.
7. Maintain situational awareness. Memorize escape routes. Locate exits, alarms, first aid kits and safety equipment.
8. Do not disable cabinet interlocks or other safety equipment.

With 50+ years experience I have seen and read first hand reports of terrible injuries. The worst electrocutions seem to happen to seasoned experienced workers who forgot a safety rule or made a simple mistake such as wearing a watch or prized jewelry. To this day I eschew wearing jewelry and always keep one hand in my pocket working in hazardous environments. Stay alert. Remain safe.

Your right, these are good ideas. But in my experience, working for decades in EE labs with dangerous stuff, people won't do these things. Safety rules need to be realistic or people won't actually do them.

My rules:
1) Don't touch things (i.e. connect equipment) when the power is turned on, unless you absolutely have to.
2) Always know how to shut it off ASAP, and allow access to that switch at all times. One switch, not a procedure. You'll do the orderly shutdown when it's not sparking and on fire.
3) As much as possible don't work in really crowded or messy spaces. When the 5V capacitor explodes, scares you, and you try to get away, you don't want to trip and hit your head on the network analyzer cart. Network analyzers are expensive.
4) Don't work on circuits you don't understand. Don't hire people that don't know what they are doing. Don't tell your technician to do things they don't understand. It's your job to know what you are doing, go back to your desk and study some more. Dunning-Kruger would be the first thing you should study.
5) Think first, every time, before you do anything. How could you (or others) get hurt? Are your assumptions correct? Don't be in a hurry (as much as possible, anyway). You can afford to pause for 10 seconds to think about what you are about to do. Make that a habit, if you can.
6) Don't "float" test equipment at dangerous voltages. There is ALWAYS a better and safer way to make measurements. Use the right equipment, in the right way (you'll also get better data that way).
7) Be especially careful the first time you apply power to a circuit/system. Do it from far away with a broom stick if you can. Expect it to explode.
8) Put signs up to scare people away from your bench when you leave dangerous things running. Don't build booby traps for the guy that wants to borrow your DMM.
9) Be scared. Always be a little bit scared (sometimes a lot scared). Always. Always.

If you do get hurt, it won't be because you didn't have the right shoes, didn't know where the fire extinguisher or first aid kit is, had a cup of coffee next to your oscilloscope, didn't have someone in the lab with you, or were wearing earrings. It will be because you did something stupid.

So, if you understand and think about the risks, and if you are still a bit scared, you will put on your safety glasses, you will tie your hair back at the drill press, you will take a little extra time to sort out a better way. If the corporate safety guy puts up a poster that says you have to, it won't actually happen very often. The problem with safety rules isn't writing them. It's getting people to actually follow them.

Still, your right. Your lab is safer than mine were. You know, the ones with real people doing real people behaviors.

PS:
10) If you're working on a safe circuit next to dangerous parts, build a guard of some sort to keep you from accidentally touching things you shouldn't. Even cardboard with masking tape will do; the more complicated you make it, the less likely you'll do it next time. Saying, "I'll be careful and not do that" isn't good enough. You'll forget or be careless sooner or later. After all, your attention is on the microprocessor, not the scary bits.

 

[anorlunda]

if i can then simplify it to a simple battery circuit;
a battery circuit with a conductor between terminals,
another conductor branching off of the said conductor to the ground
would there be significant current in that ground connection conductor?

It's simpler than that. Think of this circuit (but neglect the numerical values).

R1 is the load resistance. R2 is the resistance of the person to ground, plus the reistance of ground back to the battery's grounded point. Current divides according to the standard formula for any two resistances in parallel.
Even though almost all current goes through R1, there could be an injurious or lethal current in R2. Wikipedia offers the following to help gauge severity. Note that both current and time are important. Note that both current and time are important, and that lethal effects can happen with just milliamps.

https://en.wikipedia.org/wiki/Electrical_injury

 

[Klystron]

You (are) right, these are good ideas. But in my experience, working for decades in EE labs with dangerous stuff, people won't do these things. Safety rules need to be realistic or people won't actually do them

Right you are (as Yoda might phrase it). My safety list aimed at visitors, newbies and students; your instructions include lab directors, teachers and managers who can enforce standards.

"Keep one hand in a pocket" remains a useful memory device to always be careful.

 

[Arjan82]

"Keep one hand in a pocket" remains a useful memory device to always be careful.

"And the other one is hailin' a taxi cab"

Good advice from Alanis, because you know, I'm scared of this stuff... Doesn't get any better with these posts

 

[Averagesupernova]

I'd like to point out that in post #11 the current does divide in two but do not make the mistake of thinking that since your body is in parallel with a very large load that you will be a very small part of the total current so it is safe. You would still be across full supply voltage and the shock you would receive is not relevant to the load current in R1.

 

[gmax137]

"And the other one is hailin' a taxi cab"

I always liked that song. Just looked it up, 1995... WTH!?

 

[artis]

It's funny how @gmax137 your quote reads "Alanis Morissette said:"
At first I was kind of blown away and couldn't believe my eyes that Alanis Morissette is a member of this forums and has knowledge in EE...

I personally would love to get some electronics safety advice from AC!DC

 

[DaveE]

My safety list aimed at visitors, newbies and students

Yep. Rule #10) Don't let visitors, newbies, or students anywhere near your #$%@.

 

[gmax137]

couldn't believe my eyes that Alanis Morissette is a member of this forums and has knowledge in EE

Well, you never know. Brian May (Queen lead guitar) is an astrophysicist, John Tichy (Commander Cody Lost Planet Airman guitarist) is a professor of nuclear engineering at RPI, etc.

Not sure if they are PFrs, though.

 

[genekuli]

thank you everyone but the power source for this is not grounded,
like a car battery or cap,
so the wire that is going to ground is not returning or making a circuit in that respect.
so in this case there would be no current flow through the wire (or person) going to ground right?

 

[sysprog]

Well, you never know. Brian May (Queen lead guitar) is an astrophysicist, John Tichy (Commander Cody Lost Planet Airman guitarist) is a professor of nuclear engineering at RPI, etc.

Not sure if they are PFrs, though.

Here's a link to 21 pages of front matter from Bryan May's dissertation book: A Survey of Radial Velocities in the Zodiacal Dust Cloud.

 

[Averagesupernova]

thank you everyone but the power source for this is not grounded,
like a car battery or cap,
so the wire that is going to ground is not returning or making a circuit in that respect.
so in this case there would be no current flow through the wire (or person) going to ground right?

Ground is just a word we use to define a reference. It is true most people are 'grounded' most of the time. The schematic in post #11 does not have a ground symbol but it is implied that the rightmost resistor consists of the unlucky recipient of the shock since it is across the voltage source and the person who posted it has defined it as such. Also, standing on 'ground' only completes a circuit due to the way the source is connected. Automotive schematics could quite likely contain ground symbols but your body only completes a circuit if you touch the chassis of the vehicle even though you are standing on the ground. Don't expect not to get shocked by the high voltage ignition doing this though.

 

[rbelli1]

there would be no current flow through the wire (or person) going to ground right?

Except for any part of the circuit you never intended to exist.

If the battery has a dangerous voltage across it's terminals it is wise to assume that there is a dangerous voltage difference from either terminal to surrounding objects and ground that "shouldn't" be there. If it is there than it is irrelevant if you are not touching it and "shouldn't" doesn't care about your well-being.

BoB

 

[valenumr]

Imagine you have a 120V, 20A circuit operating at full current. That means it has a total load resistance of 6 ohms. If you "introduce" yourself to the circuit by touching a terminal, you become a parallel load to ground (and you will feel a nice zing). Your equivalent resistance will usually be much greater than six ohms, unless you're standing in a pool of salt water, so it should be that a much smaller amount of current will flow through you (note, air can conduct electricity!). But if the circuit is open (off via switch), you are basically the primary source to ground.

 

[artis]

thank you everyone but the power source for this is not grounded,
like a car battery or cap,
so the wire that is going to ground is not returning or making a circuit in that respect.
so in this case there would be no current flow through the wire (or person) going to ground right?

There was a similar thread here not long ago. The idea is this. There are circuits referenced to actual Earth ground like AC mains from the local substation and there are circuits that just have ground as a label for common reference and is not referenced electrically to actual ground like car batteries.
The main difference is that if you take the example where you as a conductive path come across a live conductor and ground in the first case where the circuit is referenced electrically to actual ground a current will flow through you which will be proportional to both the resistance of your body and the resistance of the ground return path so essentially two resistances in series.

The second case where you would touch a car battery and stand on ground no real current would flow through you because the car battery circuit is not referenced to the ground you are standing on , it is floating so to speak. But there is one exception that is important. Your body is not a symbol on a schematic your body is a real physical object, the car battery is also a real physical object so all objects have some capacitance between them and also between ground. The moment you would touch the car battery at either + or - (because it's floating so any terminal counts) you would connect your body to the circuit and even though there is not a current path formed by you touching a floating circuit at one point but there is still new capacitance introduced so there would flow some initial current into your body to charge it up according to the amount of capacitance you introduce and proportional to the voltage.
This current is extremely small and at 12v DC no one can feel it ,but if the DC voltage becomes much higher then this initial charging current can increase up to potentially dangerous levels.

 

[artis]

@genekuli Look at this video, the same applies to AC lines, the helicopter is not grounded by any means but it still has capacitance to surrounding air , live wires etc. so they use a special rod and clamps to first charge up and discharge that capacitance, they don't just touch the wires with hands first because at that high voltage the even small capacitance is enough to have a current that can kill.
Capacitors block DC (but they charge up when first connected to DC) but pass AC , everything is a capacitor you are a capacitor too when you touch a battery terminal , but as I said this becomes important for battery circits only at high voltages

 

[anorlunda]

There are many ways for such an experiment to go wrong. Therefore, it should not be discussed online where children might find it with Google search and be tempted to try their own experiment.

 

[berkeman]

There are many ways for such an experiment to go wrong. Therefore, it should not be discussed online where children might find it with Google search and be tempted to try their own experiment.

An unsafe suggested experiment by the OP has been deleted, and this thread is now closed. Thank you to everybody who has been trying to help the OP understand basic electronics.