High Voltage dangerous?

[Nora]

high voltage dangerous

Hello-
I have heard 2 things that are contradictory.
One is that the amps are more dangerous than the volts. That the amps can kill you, but the volts will not.
The other is that certain codes (CE,UL) have a low-voltage directive where low voltage is defined as < 24V.

So using two examples, can anyone explain which version is less dangerous.

I have a toaster with four (20 ohms each) resistive heat load element wired in series (80ohms) and the toaster takes line voltage 220V. So the amperage is fairly low, i=V/R = 2.75A. My heat output is P=iV = 605W

I have a toaster with four (4 ohms each) resistive heat load element wired in parallel (1 ohm) and the toaster takes voltage 24V. Amps = 24/1 = 24.
My heat output is 576W.

Thanks!
Nora

 

[pauloynski]

can high voltage kill you

The problem is not the current flowing through the equipment but the current that can flow through your body. That´s the current that can kill you. A high voltage can make a large current flow through you body and kill you. Lower voltages can´t.

 

[trekkytekky]

voltage dangerous

Power is not the issue.

Typically humans have a resistance of around 5-50K ohms. So 24V to a person will create around .5 to 4mA at most of current to flow. 220v on the other hand will create a current of 4 - 45mA to flow, this current can cause the heart to fibrillate or clamp causing death.

That is why RCDs or earth leakage devices operate on current discrepancy not voltage and usually trip at 10-30mA in most situations.

 

[Nora]

high voltage can kill

How would a large current flow through the body as in 220V example?
oh- just saw second response, never mind
Thanks!
N

 

[pauloynski]

what voltage is dangerous to humans

Just place your fingers across the mains wires

 

[Nora]

high voltage through heart

Hey Paul I'm going to have to take back "you helped me"

 

[trekkytekky]

is high current or high voltage more dangerous

Paul, You forgot the ammeter in the circuit.

 

[pauloynski]

high voltage wire dangerous

It should also be mentioned that if the current doesn´t crosses through your heart it may not kill you but it can largely affect your muscles like **broken link removed**

 

[FANT]

high voltage is dangerous or high current

You have to consider the voltage as the pressure in a water pipe, instead the current as the amount of water flowing through it.
So if the pipe is open the water can flow trough it, and the amount depends on the pressure ( voltage ) and the resistance that the pipe makes agains the flow of water ( the resistance in an electronic circuit ).
The current that flows inside your body is the dangerous current not the one that flows in the apparatus.
Consider that a current of 30 mA kept for 5 second can kill you, instead a current of 100 mA for 1/100 secon can still be safe ( the effect depend on the current and time of contact ).

Mandi

 

[vistapoint]

why current dangerous for the body

The current or voltage on your heart or other critical organs is the issue. If 24V is applied on you the current through your heart is small. It's the impedance of your body that matters, not the one in the oven. It's not safe even if the current is low but the voltage is high, the major concern is still the heart. The heart operates with electrical pulses, transmited repetatively from the top to the bottom. External stimulation may breack the electrical path.
__________________________________________
low price 1/4W 1% resistors on ebay:
**broken link removed**

 

[eem2am]

why is high voltage dangerous?

hi,

i've been zapped on one bit of one hand many times by up to 50V and it did little really.

however, i believe its worse when two parts of your body touch...ie one touches power rail and one touches the ground?

i thought up to 42V was officially safe?

ie 42V referenced to earth ground?

 

[pauloynski]

volt,spænding og u

Current needs a continuous path to flow through. If you touch a high voltage wire but your body is isolated from the current return path nothing will happen, unless the voltage is so high that it sparks over the isolation material (by ionizing the surrounding air for example). If 42V is safe or not it depends on your body. If you´re using a pacemaker it can have its performance changed.

 

[mosfets.bjt]

what makes high voltage dangerous

it depends upon how much current can flow from ur body.

u can chk the which toaster is dangerous if u know the key rules.

Current passing through body
= {(resistance of toaster)/(resistance of toaster + resistance of body) }* total current passing through toaster

toaster resistance for series is 80 ohms
toaster resistance for parallel is 1 ohms

calulate it urself and tell me the answer too

voltage is something related to distance. if voltage is high, more distance from that wire is required. thats why it is usually highly unrecommanded to enter grid station having all the metal things attached to ur body. beacuse high voltage can catch u. and will cause high current to flow through ur body due to its high current driving capabillity.

power will determine how much power is being disspiated in ur resistor of toaster or how much power is being converted to heat

 

[logicon]

is high voltage dangerous?

High voltage SOURCES are dangerous especially if they have a high driving POWER source behind them. Compare it to two stones on top of a hill: one small and other big. If they both drop and hit you, the heavy will kill faster than the smaller.
Most of the comments are true. If you consider an energy storage device such as a capacitor, the amount of TIME it can discharge through your body is limited. This is contrary to a AC/DC Generator.
The impacted OBJECT is also a factor. For humans, heart is the most susceptible in the body. The nerves supplying this and the muscles are the most impacted. This constitutes the shock experience. The magnitude a fat person/wet person/lean person experience are all different. On the average if you subject the body to over 40 mA may be fatal.

 

[exorcisto]

stærkstrømsbekendtgørelsen current

High voltages can be dangerous as well as low voltage sources. A stun gun will instantly deliver approximately 50,000 volts to a person but at only around 100 MilliAmps. However, stun guns have been known to kill people in rare occasions. Are high amperage's a danger? They can be. A common Lead Acid battery of a car delivers 12 Volts and usually as much as around 500 Cranking Amps to start your car. But at that low voltage human contact with them will not cause any harm. (unless the contacts are shorted)

 

[hyhan]

kroppens modstand

Hejsa.

Ved det er lidt tid siden spg. blev oprettet, men ville lige komme med lidt kommentarer.

Der er flere faktorer der spiller ind. [trekkytekky]'s påstand omkring 5-50kOhm er lidt vildledende.

En mediciner fra New York fortalte for nylig om en person, hvis elektriske modstand skulle være 500.000 ohm, hvilket er et overordentlig højt isolationsniveau. I nævnte tilfælde må målingen være foretaget med en let berøring af elektroderne med de spidse ender af lange kinesiske fingernegle. 1000 ohm ville repræsentere modstanden i kroppen, resten selve berøringsmodstanden og fingerneglene. For at afgøre spørgsmålet lavede hr Edison nogle modstandsmålinger på mellem 400 og 500 personer, og med hans karakteristiske originalitet udviklede han midler, hvormed der blev opnået ensartede testbetingelser. To krukker fyldtes med en svag opløsning af kaustisk potaske og blev forbundet til måleapparaturet. Hver person dyppede sine udstrakte hænder i væsken indtil enderne af langfingrene ramte bunden. Hænderne var nedsænket i 30 sekunder før et måleresultat blev noteret. Denne forsinkelse tillod potasken at reagere med olien i huden, idet denne blev omdannet til en sæbeopløsning i vandet, hvorved berøringsmodstand og modstand i overhuden blev praktisk talt elimineret.

Den gennemsnitlige modstand blev bestemt til 1000 ohm. Det højeste måleresultat var blot 1970 ohm. Variationen skyldtes uden tvivl arealet af hudoverfladen, der var i kontakt med væsken, eftersom antallet af ohm pr kvadratcentimeter overflade var praktisk talt det samme i alle de tilfælde, hvor arealet blev målt. Rapporten udarbejdet af hr Edisons ledende elektriker, hr A. E. Kennelly, er yderst overbevisende. I mere hverdagsagtige tilfælde, hvor huden ikke med hr Edisons metode er blevet specielt forberedt til at modtage strømmen, viser det sig, at strømpassagen hurtigt reducerer modstanden i overhuden ved at bringe mere saltholdige væsker dertil. Jo større spænding strømmen har, jo hurtigere falder modstanden.

[Oversættelse fra The North American Review, november 1889]

Yderligere varierer kroppens modstand sig meget alt efter den spænding den bliver påtrykt.

Fra samme kilde (Stærkstrømsbekendtgørelsen Afsnit 2, Udførelse af elfor­synings­anlæg) kan det erfares, at kroppens impedans (modstand) er forskellig, alt efter hvilken spændingsforskel den påtrykkes. Jo større spændingsforskellen er, jo mindre bliver kroppens modstand. Ved en spændingsforskel på 25 volt mellem en hånd og en fod skulle der være ca 3250 ohm, mens der ved en påtrykt spænding på 1000 volt kun er 1050 ohm mellem de to legemsdele.

Yderligere reagerer kroppen, og dens ohmske modstand, forskelligt på om det er Jævn- eller vekselspænding.

Omkring punktet med de 24/42 volt mener jeg det er gamle regler. Under L-AUS kurserne mener jeg det hedder: "Arbejde på installationer og tavler under spænding", og er teknisk set fra du skal skifte batteriet i dit ur. Jeg er ikke 100% sikker på dette område, men mener det burde kunne findes i Stærkstrømsbekendtgørelsens. Men området hedder L-AUS, og man kan sikkert Google sig til en masse viden omkring området.

 

[ark5230]

overflade resistivitet ohm

Nora's toaster works at 24V and takes 24A of current as claimed in the very first question. Can some one guide me if it is a realistic situation. What conductors are sued. What 24 V, 24 A source might be used for what duration !

 

[threephase]

To answer what is probably a hypothetical qustion, two 12V car batteries in series would provide 24V with enough current capacity. Wires of cross section 2.5sqmm would carry the 24A without any issue.

This makes me hungry - I think there's a bread crust somewhere that I can scorch by radiation from an electrically heated resistance wire.

3phase

 

[karesz]

Hi alls,
One other aspect for danger of life is: DC or AC?
Dc is fataler becaouse you becomes bubbles of oxygen & hydrogen in your blood and the end of your life comes rash...
K.

 

[sheraz.pervaiz]

I disagree that DC are more fatal, actually AC are more fatal. 60 Hz frequency system is usually more dangerous than 50 Hz system, b/c our muscle response for 60 Hz tends is to contract. That means if we touch a wire of 60 Hz, chances are more that our hand will involuntarily grasp the wire, thus current will flow for longer duration.

DC system was norm of older days, but since the advent of transformer (w/c works only on AC), linelosses were greatly educed, and AC system was much more feasible.

Thomas Eddy, the inventor of bulb, and many other electrical devices. His devices works on DC systems, which he has patent for, earns a lot of royalty. But after the popularity of AC soon his royalty starts to decrease. Now there was no advantage of DC except that it was much more safe. To illustrate this, electric chair was invented, which works on AC.

In short, the fatality of shock depends upon.
Amount of current
Frequency, and it which phase is your heart
Duration of shock