Matter of interest...

[AdamW]

I was just thinking. As I have always been careful with electricity and take any precautions short of climbing inside a rubber suit, I have never got a shock off mains electricity.

However, if somehow I did end up touching the business end of a live cable, how bad is the shock you get before the RCD shuts it off? Is it dangerous?

What about a fuse? Would a standard wire fuse on the CU blow if you earth the live (either through yourself or the earth wire)?

 

[Big_Spark]

I was just thinking. As I have always been careful with electricity and take any precautions short of climbing inside a rubber suit, I have never got a shock off mains electricity.

However, if somehow I did end up touching the business end of a live cable, how bad is the shock you get before the RCD shuts it off? Is it dangerous?

What about a fuse? Would a standard wire fuse on the CU blow if you earth the live (either through yourself or the earth wire)?

You should not feel a thing if the circuit if RCD protected as the minimum is only 10mA above the threshhold for a potentially fatal shock, as such they are designed to disconnect the supply so quick it should not register.

As for a fuse..that depends on the size of the fuse, the type of the fuse, the size and type of circuit and most importantly, how quick your reactions are

 

[il78]

Worst shock I had is the one that split my forehead open.....

Working in a residential home in the loft connecting up a fan when the apprentice thought it would be interesting in turning the isolator back on....at the time, cable in my hand, kneeling on some metal tray (summer time with shorts on).....nice shock (felt like a bomb had gone off as my eye sight went completey white) and then head butted a water pipe in front me due to the shock, not because I got angry.......

Went through some insulation tape that day.....it keeps apprentices where you want them

any-hoos....

apparently there is video footage of some scientist testing out on himself the ratings of RCD's before shock levels get too much......

 

[ban-all-sheds]

Many years ago, whilst fiddling with an amplifier I was building, I managed to touch a live thing with one hand whilst grasping an earthed thing with the other. (This was pre-RCD days)

I wouldn't say that it hurt, but there was a very unpleasant physical vibration (50Hz), and I could feel the muscles in my arms and across my chest tighten up. Frightened me absolutely sh|tless....

No burns either.

The house had a TT supply, and was built on a hill, on well-draining chalky soil, which may have helped preserve me. Who knows? - if Ze had been 2 orders of magnitude less than it probably was, I might never have been here to harangue you all....

Do not try this at home.

The value of your life can go down as well as up.

If in doubt consult a qualified doctor.

 

[AdamW]

One of the reasons I was interested in this was because back at school a friend and I decided to turn off the juice at the circuit breaker (physics lab, so CB mounted where it could be reached in a hurry), then with a pair of long thin scissors jammed one prong into the earth terminal (thus revealing live and neutral). Then the second probe was pushed into the live terminal, and the socket switch turned on.

You can imagine what came next: circuit breaker switched back on, loud bang from socket and scissors, breaker cuts out, scissors welded to socket.

Now, I am guessing that was NOT an RCD, as that surely would have cut out before any schoolboy shennanigans could have come to fruition.

I will leave my stories of reverse-biased diodes and electrolytic capacitors for another day...

 

[AdamW]

As for a fuse..that depends on the size of the fuse, the type of the fuse, the size and type of circuit and most importantly, how quick your reactions are

What I really meant was, with an old fashioned 20A fusewire in ceramic holder, what would blow first? Fuse or spark?

 

[Kimba]

I think if you had 20A of current flowing from say a limb to you foot, you will be in serious trouble (fatal). So Spark

Although what's far more likely is spark touchs live wire, being AC there is no problem associated with muscles contracting fully, and spark would therefore pull his hand away as a natrual reaction, probably with a bit of jumps, and the odd french language... althogh this may just be directed at the gimp who turned the circuit back on.

 

[securespark]

You're gonna think this atrocious, but I was left to my own devices to fiddle with electricity, and the first shock I can remember was aged 9. It didn't hurt, although it was a very odd sensation.

The following will hammer home that age-old saying which everyone must chant after me, "NEVER assume anything when dealing with electricity"

I was working on first-floor ring, pulled out the 3036, used volt stick to check (wasn't working! - ALWAYS check v.s is working b4 relying on it!!) and chopped thro' L & N with side cutters - huge BANG!

The funny thing was, the 30A 3036 was still intact!!

THIS NEXT BIT IS NOT TO BE TESTED - DON'T DO THIS AT HOME, CHILDREN!!


My boss used to show me how being on the first floor of a dwelling with timber floor meant you were well insulated from the earth, and could grab hold of lighting lives and not feel anything at all.......


REPEAT- DO NOT TRY THIS UNDER ANY CIRCUMSTANCES!!

 

[Big_Spark]

If you want to be scared, then the truth is that 70V is all that is needed to push 20mA through a human body in DRY conditions, and this charge will possess the energy to KILL in the right circumstances.

This is why construction sites use 110V (2 X 55V) supplies. They are classed as SELV (Safety Electrical Low Votage) circuits.

I had a 3 phase wack a few years back working in a boarding school.

I was in the panel, an old Doorman-smith unit, panel had the main isolator turned off as I was removing and replacing breakers and this involed loosening a restraining bar.

Anyway, this kid had been bullied by some other kids and he came running inside to hide, pushed this fire door open, slammed it into me, I fell forward and hit the Isolator, this happened to be UP=OFF and ON=DOWN, so I turned it on with my left hand as my right hand went onto an exposed MCB connector tab whilst my left elbow hit a row of exposed tabs on the other side of the panel!!

I was burnt slightly on my fingers and elbow, and had the fastest heartbeat in Christendom for about 5 minutes..I do not recommend it!!

 

[ban-all-sheds]

One of the reasons I was interested in this was because back at school a friend and I decided to .....

see here

 

[waran]

You might be interested in the following:

Current Intensity Probable Effect
1 mA Tingling sensation; almost not perceptible
16 mA Maximum current a person can grasp and “let go”
7–9 mA “Let-go” current for an average man
6–8 mA “Let-go” current for an average woman
3–5 mA “Let-go” current for an average child
16–20 mA Tetany (repeated contraction holding person to source) of skeletal muscles
20–50 mA Paralysis of respiratory muscles; respiratory arrest
50–100 mA Threshold for ventricular fibrillation (heart stops)
>2 A Death

AC because of it's alternating nature is about 3 times worse than DC - (Edison first advised the use of it for electrocution! ) The nature of the injury depends on both the current and its duration. With AC repeated contraction of the muscles means you are less likely to be able to withdraw your hand compared to DC.

Obviously voltage plays a part in the current passing through your body. But skin has a high resistance (about 40 - 100000 Ohms for a man) and can effectively resist a low voltage shock lessening the current load to about 2mA which should be tolerable to a hard caloused tough skinned sparky. A child with thinner skin may not be so lucky!
Obviously the presence of water (i.e. sweating) can reduce the skin's natural resistance. And if the contact was through the mouth etc......

The internal resistance of the body is about 500 - 1000 ohms and damage is also dependent on the pathway the current takes.

A potentially serious complication of an electric shock is injury to the heart causing direct damage or rhythm disturbance.

The other main injury is burns which can be caused by the direct contact and can be internal, or can be of the 'flash' type with no direct contact. Typically with low voltages they are superficial and will heal well. Again contact time surface area and current are determinants of the severity of injury. It's been quoted that you require at least 20 secs to a current of 20 mA/mm2 to produce a burn. Obviously with higher currents you require less contact time.

With high voltage injury the risk of damage to other organs etc is quite high.

It might interest you to know that statistically you are more likely to suffer a fatality from electrical injury if you work on industrial/ large commercial sites with exposure to over head high voltage current. Young (20-34) inexperienced males especially are at higher risk and those working for small (less than 10 employees) firms.

SO TAKE CARE OUT THERE!

You probably all know this already but if you do witness a significant shock make sure that it is safe for you to approach the victim before aiding them.

If you do get a significant shock but think you're alright it might be worth going down to A & E to get an ECG (electrical tracing of the heart) done. Especially if you have any history of heart disease or you get a burn / feel any palpitations!

BUT to reiterate what's already been said many times - if you don't know what you're doing and how to do it safely, please don't do it!

 

[Big_Spark]

AC because of it's alternating nature is about 3 times worse than DC - (Edison first advised the use of it for electrocution! ) The nature of the injury depends on both the current and its duration. With AC repeated contraction of the muscles means you are less likely to be able to withdraw your hand compared to DC.

Although I agree in terms of damage that can be caused by a given voltage AC is worse as it usually contains more energy that statement is inaccurate, DC is far worse than AC for one very simple reason..

DC contracts muscles and therefore PREVENTS the victim from releasing any grip they may have had on the source of energy.

AC can and does cause muscle spasms, but usually this results in the person being disconnected from the source of energy.

Voltage alone can kill, regardless of the current on the circuit, although rare, due to the nature of electrical sources we can come in contact with, it can and does occur.

Current alone is USELESS at causing death. A 10Vac circuit with 50A in it will not be fatal to a human as 10Vac is unable to "push" this current through the human body.

This is why you have ELV,LV and HV circuit definitions.

ELV, or Extra Low Voltage circuits are defined as either SELV or PELV and do not normally exceed 50V ac rms or 120V ripple free dc

LV, or Low Voltage circuits normally exceed ELV but do not exceed 1000V ac rms or 1500V ripple free dc

 

[securespark]

But isn't the reason for shorter disconn times on rings because of the risk of muscle spasm if encountering faulty hand-held equipment??

 

[AdamW]

You probably all know this already but if you do witness a significant shock make sure that it is safe for you to approach the victim before aiding them.

All of the Health and Safety stuff I have seen recommends breaking contact between the victim and the supply with a wooden broom handle.

I had a 3 phase wack a few years back working in a boarding school.

Ouch ouch ouch!!!

Current alone is USELESS at causing death.

Hence the reason that most schools use low-voltage dc supplies during experiments. In A-level I mainly used 2-volt lead acid accumulators (i.e. 1 sixth of a car battery!) that could produce 500A dc but were relatively safe to human contact as the potential difference is so low. So even with a potential kilowatt of power there were no electric shocks. A few blown semiconductors maybe, but no burns or fibrillations!

 

[breezer]

did you know......

Firemen when checking a building where they can not see (apart from the other things they do) will slowly raise and lower one arm (palm pointing towards body) to "see" if any obstructions are in the way, if they touch a live cable the natural reaction is for the hand to close, so palm pointing towards body means when hand closes it will not grab the live cable as you may if you had palm facing outwards