What is the path current takes in an electric shock.

[Jako13!]

Hi I am currently doing my electrical NVQ and have asked a few electricians this question and wanted to clear things up. If we touch an electrical conductor and are standing on the mass of earth will the current flow through us and back to the transformer or just dissipate into the ground. I’m confused as I’ve also been told when insulated from Earth we can still receive a shock due to the bodies capacitance.
Thank you for your help in advance.

 

[dmxtothemax]

QUOTE - #1 If we touch an electrical conductor and are standing on the mass of earth will the current flow through us and back to the transformer or just dissipate into the ground. I’m confused as I’ve also been told when insulated from Earth we can still receive a shock due to the bodies capacitance.
The current will always seek to return from whenst it came !
So it will return to the transformer via the ground.
Remember the transformer secondary is usually grounded
It does not just dissipate into the ground.

And yes capacitive and inductive coupling is real,
so shocks and tingles can also come from coupling as well.

 

[Lucien Nunes]

A current always requires a complete circuit. The mass of earth is just another conductor that leads back to the earthed neutral point of the supply transformer. It's quite a good conductor and it's available everywhere, although it's hard work to make a really good connection to it (think of the Ra of an average rod, versus a terminal block!) A shock to the mass of earth merely uses the earth as one part of the complete circuit, instead of a metallic conductor such as the CPC.

Yes, you can receive a shock when standing on an insulator, because the stray capacitance between your body and earth very slightly bypasses the insulator. Capacitance occurs between the surfaces of any two conductive objects. In an actual capacitor they are two sheets of metal foil deliberately placed close together. There's capacitance between a knife and fork lying on the table, and between every conductor in an installation and everything else. Small currents can flow through these capacitances, usually too small to be of interest because the capacitance presents a high impedance at 50Hz. In this case the capacitance is between the surface of your body and the surfaces of any nearby earthed objects, including the mass of earth. The shock current flows from the live conductor into you, through the capacitance between your body and earth, then through the earth back to the earthed neutral of the supply transformer as usual.

It might not look like a complete circuit because of the insulator, but the capacitance completes it.

PS I have no idea why there is a table in the middle of the post. I can't delete it. (Fixed it - SC)

 

[Jako13!]

Thank you for your reply’s. But how does using insulating rubber mats and boots help with reducing shock as we still have a capacitance value.

 

[DPG]

Thank you for your reply’s. But how does using insulating rubber mats and boots help with reducing shock as we still have a capacitance value.

Yes but a thick rubber mat makes a poor dielectric.

 

[Lucien Nunes]

The shock current depends on the total impedance of the circuit. The impedance of the stray capacitance is high at 50Hz, high enough to limit the current to a safe value. I just measured my stray capacitance - about 180pF standing in the middle of the floor but nearer 300pF standing next to a bunch of earthed stuff. Xc=1/(2.PI.f.C) = 11MΩ. Touching something live at 230V to earth would give a shock current of 230/11M = 0.02mA. You can feel that sort of current if you stroke a live surface with the back of your hand but not as an actual shock, it's too low, and it won't hurt you.

Standing barefoot on a damp surface, the resistance is likely to be 1000 times lower and the current 1000 times higher, which is getting towards dangerous levels with a definite ouch factor and into RCD-tripping territory.

 

[marconi]

Mmmm..... Always makes me nervous when folk are curious and start asking about electric shocks and electrocution. On a living body electricity has a number of physical(one being heat) and physiological effects(eg: interference with the heart's nervous system) which is comprised of complex interconnection and interaction of muscles, tissues, nervous system, brain, and skin (- the largest organ of a body) - readily attacked by free-flowing electricity.

No tutorial from me - but learn to treat electricity with the utmost respect (whatever the voltage and current) and thereby stay alive - it is the one's left behind who grieve - which is not an academic subject.

In six decades I have had three mains voltage shocks - aged 4 (curious and too young to know), 14 (made a mistake in checking correctly something was dead - did not check cpc!) and 42 (even though I turned off all the main switches in a flat ( - another story about E7 installation for another time ) - but I should have proved dead as well). They really hurt. All three my own fault.

 

[static zap]

Dampness is probably your enemy when it comes to capacitance , it's a variable quantity . So not to be trusted !
Capacitance will get you that vibrating tingle from cheap double insulated DVD players / phone chargers !
A lesson on " Safe isolation " is more appropriate for beginners !
--And fibre glass steps -just in case--

 

[ipf]

My worst was about 40 years back. Working in a factory on a live board, no other choice, when, believe it or not, the idiot apprentice (not mine) holding the ladder decided to pi$$ about. Driver slipped and I went straight onto a phase bar and touched another with my elbow, whilst holding the unit. I slid down the ladder and banged him up against the wall. Two minutes later I was shaking like a leaf with a black arm. A couple of nasty little burns but it looked worse than it was. Extremely lucky.
Made a mess of the driver, too.

 

[DIYer Gaz]

The shock current depends on the total impedance of the circuit. The impedance of the stray capacitance is high at 50Hz, high enough to limit the current to a safe value. I just measured my stray capacitance - about 180pF standing in the middle of the floor but nearer 300pF standing next to a bunch of earthed stuff. Xc=1/(2.PI.f.C) = 11MΩ. Touching something live at 230V to earth would give a shock current of 230/11M = 0.02mA. You can feel that sort of current if you stroke a live surface with the back of your hand but not as an actual shock, it's too low, and it won't hurt you.

Standing barefoot on a damp surface, the resistance is likely to be 1000 times lower and the current 1000 times higher, which is getting towards dangerous levels with a definite ouch factor and into RCD-tripping territory.

With regards to your information, the electric cooker in my kitchen has a power supply of 230v - 50hz. Max power supply is 4.07kW. Fuse is 20amps. I was foolish enough to touch the live wire whilst standing barefoot on my kitchen floor. This did send an almighty shock through my right arm, I did feel my heart skip a beat and despite being aware of everything going on, my eyesite went black for a second. So I have no burn marks that I can see anywhere, feet, head arm etc. I have tested the RCBO trip and it does trip when pressed, however, the circuit never tripped when I touched it, any idea why this would be and what level of resistance do you think would have been present in this situation? Thanks for any info.

 

[telectrix]

the current passing through you was either < 30mA , less than 300mSec., or both.

 

[marconi]

DIYer Gaz: You have done a service relating your story and I hope you dine off it with chums and colleagues.

May I put the incident in context - are you in a relationship with anyone? Do you have children that rely on you? Are you the main breadwinner? I have had to deal with the aftermath of what happens when the outcome is death leaving a 24 years old wife to start working while looking after 3 infant school age children. Your story illustrates why it is well worth employing a professional to do what might seem a simple job; he/she knows how to ensure their own safety.

Can I put you on the spot - why did you not turn all the electricity off? I did when a I replaced a defective double socket this weekend - and tested with an approved device it was dead. If I die my disabled, sick wife is stuffed until she is called by the Holy Spirit and goes to a better place. So I don't take the risk - no shame in that.

You have had an easy time from others but not from me - you were a berk and lucky to be alive.

 

[DIYer Gaz]

DIYer Gaz: You have done a service relating your story and I hope you dine off it with chums and colleagues.

May I put the incident in context - are you in a relationship with anyone? Do you have children that rely on you? Are you the main breadwinner? I have had to deal with the aftermath of what happens when the outcome is death leaving a 24 years old wife to start working while looking after 3 infant school age children. Your story illustrates why it is well worth employing a professional to do what might seem a simple job; he/she knows how to ensure their own safety.

Can I put you on the spot - why did you not turn all the electricity off? I did when a I replaced a defective double socket this weekend - and tested with an approved device it was dead. If I die my disabled, sick wife is stuffed until she is called by the Holy Spirit and goes to a better place. So I don't take the risk - no shame in that.

You have had an easy time from others but not from me - you were a berk and lucky to be alive.

Tha ks for the reply and the honesty. I am actually at the hospital as I write this for checks. I was never intending to touch anything but the plastic face if the wocket due to a loose panel however I agree 100% with your instructions. The doctor just told me home electrics would not be enough to sustain any lasting damage. Hopefully this is true but I know you guys are the experts in electricity. I have a RCBO however this did not trip so I will be getting a professional in to run some tests on the unit and to check the cooker mains.

 

[James]

Tha ks for the reply and the honesty. I am actually at the hospital as I write this for checks. I was never intending to touch anything but the plastic face if the wocket due to a loose panel however I agree 100% with your instructions. The doctor just told me home electrics would not be enough to sustain any lasting damage. Hopefully this is true but I know you guys are the experts in electricity. I have a RCBO however this did not trip so I will be getting a professional in to run some tests on the unit and to check the cooker mains.

Although in this case the doctor has told you that home electrics would not be enough to cause lasting damage, I WOULD LIKE TO STRONGLY DISAGREE.
you have been fortunate and because you have survived means you have a great chance of not having any lasting damage.
however,
home electrics are OFTEN FATAL, so i think the doctors advice is misleading at best, outright WRONG at worst.

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=18&ved=2ahUKEwjBzIP6v6zpAhXiQUEAHblmCNEQFjARegQIBxAB&url=http%3A%2F%2Fwww.owengibbselectrical.co.uk%2Fdownload%2Fi%2Fmark_dl%2Fu%2F4011918444%2F4593610261%2FElectrician_Downloadable%2520RCCDs.pdf&usg=AOvVaw3jMbDcWIfH4gsVVrvvSll1

70 people a year might not seem a lot but they were ALL AVOIDABLE.

 

[DIYer Gaz]

Although in this case the doctor has told you that home electrics would not be enough to cause lasting damage, I WOULD LIKE TO STRONGLY DISAGREE.
you have been fortunate and because you have survived means you have a great chance of not having any lasting damage.
however,
home electrics are OFTEN FATAL, so i think the doctors advice is misleading at best, outright WRONG at worst.

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=18&ved=2ahUKEwjBzIP6v6zpAhXiQUEAHblmCNEQFjARegQIBxAB&url=http%3A%2F%2Fwww.owengibbselectrical.co.uk%2Fdownload%2Fi%2Fmark_dl%2Fu%2F4011918444%2F4593610261%2FElectrician_Downloadable%2520RCCDs.pdf&usg=AOvVaw3jMbDcWIfH4gsVVrvvSll1

70 people a year might not seem a lot but they were ALL AVOIDABLE.

Thanks for getting back and for the information. I had a strong feeling the information was misleading.