240v AC that will not give shock !?

[grim]

240v won't kill you. just ask the birds sitting on the overhead cables

that's the everyday example of an earth free circuit.

the important bit is '240v with referance to'

in the case of birds on a wire, in referance to nothing at all, so they are fine

in a normal home supply live is 240v in referance to earth and Neutral

an isolation transformer means the isolated live is only dangerous if you touch the isolated neutral - referance to earth has been removed.

a thick rubber mat means you are not earthed, so can touch a wire that is at 240v above earth - in this case you are the bird on the wire

nothing will help you if you touch live and neutral at the same time, hence hand in pocket.


and an earth leakage breaker is not much use, if you use an isolation transformer



persoanlly I have always used an isolation trany in test labs, and i know as long as i only touch one terminal, i am ok.

 

[Nigel Goodwin]

nothing will help you if you touch live and neutral at the same time, hence hand in pocket.

240V is rarely fatal even then, you have to work really hard to kill yourself on 240V, or be seriously unlucky.

 

[Reloadron]

Actually like the bird on a wire a half million volts won't kill you long as there is no path to ground. Actually maybe better put a much lower potential. For those who have never seen it, this video clip is pretty cool.

Ron

 

[Hero999]

Here's a question:

The helicopter wasn't connected to ground so why was there still a huge spark when it came into contact with the power line?

Surely if he's not earthed, he doesn't need to wear a Faraday cage?

Answer:
The helicopter still has capacitance to earth, enabling a current to flow, causing sparking.
Suppose the capacitance is 200pF, the voltage is 400kV and the frequency is 60Hz, the current would still be 30mA which is enough to cause a severe, if not even potentially letlal shock so a Faraday cage is still necessary.

 

[Reloadron]

Here's a question:

The helicopter wasn't connected to ground so why was there still a huge spark when it came into contact with the power line?

Surely if he's not earthed, he doesn't need to wear a Faraday cage?

Answer:
The helicopter still has capacitance to earth, enabling a current to flow, causing sparking.
Suppose the capacitance is 200pF, the voltage is 400kV and the frequency is 60Hz, the current would still be 30mA which is enough to cause a severe, if not even potentially letlal shock so a Faraday cage is still necessary.

My guess is that the helicopter although not at ground potential was not at the same potential as the transmission lines. The arc was caused by the difference in potential. Once the helicopter was at the line potential the arc ceased.

Likely a lousy analogy but we can have a lightening strike to ground, however, we can also have lightening from cloud to cloud as long as the potential difference is there. On another note, under the right conditions, like a dry winter day, I can walk across a rug and build up a static charge. I can then reach for an ungrounded door knob and draw an arc.

As to the suit? Beats me and I wondered about it. A man on a wire at the potential of the wire should have nothing to worry about. Much like the bird on a wire and I never saw a bird in a Faraday suit?

<EDIT> Sneaky with the font colors and size huh? That was good Hero! I had a gut feeling you sure weren't really asking. So why don't birds without a suit become roasted birds?</EDIT

Ron

 

[joespaz7]

your right, you won't get a shock. but you WILL burn your fingers off. =P

 

[Nigel Goodwin]

As to the suit? Beats me and I wondered about it. A man on a wire at the potential of the wire should have nothing to worry about. Much like the bird on a wire and I never saw a bird in a Faraday suit?

It's an extra precaution, I'd much sooner wear the suit!

 

[Reloadron]

Thanks Nigel, I figured it was likely a precautionary measure.

Ron

 

[Hero999]

My guess is that the helicopter although not at ground potential was not at the same potential as the transmission lines. The arc was caused by the difference in potential. Once the helicopter was at the line potential the arc ceased.

Likely a lousy analogy but we can have a lightening strike to ground, however, we can also have lightening from cloud to cloud as long as the potential difference is there. On another note, under the right conditions, like a dry winter day, I can walk across a rug and build up a static charge. I can then reach for an ungrounded door knob and draw an arc.

Well I know helicopters generate static electricity so that's not a bad theory but the arcing did seem to be at mains frequency, if it was static, the frequency would depend on the length of the arc.

As to the suit? Beats me and I wondered about it. A man on a wire at the potential of the wire should have nothing to worry about. Much like the bird on a wire and I never saw a bird in a Faraday suit?

<EDIT> Sneaky with the font colors and size huh? That was good Hero! I had a gut feeling you sure weren't really asking. So why don't birds without a suit become roasted birds?</EDIT

I suspect it's because birds are much smaller than a bit huge metal helicopter so will have a tiny capacitance which won't allow a lethal current to flow.

 

[Instrotech]

240V is rarely fatal even then, you have to work really hard to kill yourself on 240V, or be seriously unlucky.

Hi , i was just searching for a little infomation on the net and found this forum and thread .
First time poster "and i know this is an old thread but....."

Dude i do not think that is a good comment to make

 

[Nigel Goodwin]

Hi , i was just searching for a little infomation on the net and found this forum and thread .
First time poster "and i know this is an old thread but....."

Dude i do not think that is a good comment to make

You have a problem with the truth?.

 

[Reloadron]

You have a problem with the truth?.

I still don't know which comment?

Ron

 

[unclejed613]

i get bit about once a year by 120Vac... not fun, but i'm still here.... always use the "One Hand Rule"... i.e. never work on something live with both hands... also, i've adapted the first rule of handling firearms "Always assume it's loaded..." to "always assume it's live... i have been bit enough times by charged caps long after the device was turned off and unplugged (that goes double for CRT picture tubes!!!!!!). i've got in the habit of discharging caps in amplifiers and the primary side of switching supplies before i do anything else. "back in the day" the saying was (and this was about vacuum tube power supplies that had bleeder resistors) "always assume the bleeder resistor is open". i used to work with someone who would identify 120V and 240V circuits by grabbing both exposed wires quickly between his index finger and thumb.... i never liked working on TVs with him much....

 

[Instrotech]

Dude i don't want to get into an argument,but let's be honest , is not the truth ! unless you work with some new type of current flow maybe wireless ? LOL "sorry for the joke "

240V is rarely fatal you say ? Dead people do not complain,you might get 10 electrical shocks and live "these people are lucky if they are not burned or have loss of feelings due to nerve damage or even have heart damage , but you will only ever get one electrocution,as dead people do not complain"

You have to work really hard to kill yourself on 240V you say?Seriously touch 100amps at 240 volt to earth or neutral and see what happens! or jam a screw driver in a single phase high current board and see what sort of prospective fault current comes through, and let me know will you ? "seriously do not do that !"

seriously unlucky Well this is pretty simple there is no luck, just Do not work a live circuit!"really, you only get once chance with electricity "

You might think, i have posted to get all argumentative or cause trouble, the fact is i did not intend to do this , all i wanted to say is that your comment makes out that ,it is ok to work on 240 volt and is pretty safe "when really, it is not and that is the truth !" I am sorry if i have offened you in anyway what so ever , but a comment like that is very dangerous to some people.As they say "A person with a little knowledge about electricity is more dangerous than a person without that knowledge of electricity" simply someone who knows nothing about it ,will not be so enthusiatisic to play with it.



P.S there is some pretty good info on this site , and i am off to read some of it.

 

[Instrotech]

If you get a shock , you should get your heart checked , simply beacuse an electrical shock can put your heart out of rhythm.It happened to a person i used to work with , he got a belt of a 10 amp supply and he died 16 days later due to his heart was out of rhythm.

 

[Nigel Goodwin]

240V is rarely fatal you say ? Dead people do not complain,you might get 10 electrical shocks and live "these people are lucky if they are not burned or have loss of feelings due to nerve damage or even have heart damage , but you will only ever get one electrocution,as dead people do not complain"

Only a very tiny number of people will be killed, or even suffer any ill effects from a 240V electric shock. Certainly only a tiny fraction of 1%, I would consider that an accurate application of "rarely fatal".

You have to work really hard to kill yourself on 240V you say?Seriously touch 100amps at 240 volt to earth or neutral and see what happens! or jam a screw driver in a single phase high current board and see what sort of prospective fault current comes through, and let me know will you ? "seriously do not do that !"

Doesn't matter if it's 100A circuit or 10A, the potential for injury or death is probably identical - and jamming screwdrivers across circuits has nothing at all to do with it?.

seriously unlucky Well this is pretty simple there is no luck, just Do not work a live circuit!"really, you only get once chance with electricity "

I would consider a tiny fraction of 1% to be pretty unlucky? - perhaps you wouldn't.

I can only imagine you come from a 110V country?, and have an inbuilt fear of anything higher - as far as I'm aware just as many people die of electric shocks in 110V countries as in higher ones.

 

[JimB]

Its the volts that jolts, but the mills that kills!

If you get your hand across the mains input connector in some equipment, you will shout and swear and drop the thing very quickly.
Small points of high resistance contact to the skin, not hand to hand, is unlikely to seriously hurt you. (Been there done that, got the T-shirt, several times).

However, good contact, hand to hand across a 240v supply buss bar will seriously hurt you.

You just need to know the risks and take the appropriate precautions.
Just look in the mirror to see who is responsible for your safety.

JimB

 

[tvtech]

Hi All

The very first thing I learn't as a TV Tech was to keep one hand in my pocket when anywhere near the Line Output Stage....

The older TV's had a Line Output Transformer that had a bare pin which connected to the trippler.....around 7.5KV could bite you there.

Has served me well over the years.

Cheers

 

[Nigel Goodwin]

However, good contact, hand to hand across a 240v supply buss bar will seriously hurt you.

Just as the same thing with 110V will

Obviously the higher the voltage the more dangerous, but you still have to be unlucky (or seriously stupid) to get killed by 240V.

Incidently, a quick google finds a few figures - in the UK in 2001, 2002, 2003 (when statistics stopped been collected) there were roughly 8000 cases per year of electric/radiation accidents - not deaths, accidents.

Not a terribly informative statistic to be honest, as it's much too vague.

 

[ronv]

Here is an informitive link.

Electric Shock Hazards