If amps kill, then why are there "high voltage" signs?

[Mixolydian42]

If amps kill, then why are there "danger: high voltage" signs outside electrical transformer stations? If a signal is high voltage, wouldn't it be low current, meaning it's not dangerous at all? Or can voltage be dangerous as well?

[Danny (NS::U)]

It all goes back to Ohm's law. Power=VoltageXCurrent

 

Any electrical current of sufficient intensity can kill you handily. You can have very high voltage and very high current (like what's flowing through that electrical substation, which is deadly), or a ton of voltage with low current (getting shocked on a doorknob).

 

I might go so far as to say that the truism "amperage kills" should probably be thrown out, and replaced with "energy kills." (Just my opinion.) In any case, the bottom line is that high voltage does not necessarily mean low or high current - you have to take into account the other side of the equation (the power) to really know how the proportionality is happening.

[Mackin]

I got shocked today ...

...bad grounding on my buddy's PA amp... well in fact, no ground prong at all on the extension he had brought.

fucking dollarstore cables...

[MrKnobs]

If amps kill, then why are there "danger: high voltage" signs outside electrical transformer stations? If a signal is high voltage, wouldn't it be low current, meaning it's not dangerous at all? Or can voltage be dangerous as well?

 

There's actually a very narrow range of current that puts the heart into fibrillation. Below that amount is harmless, above it clamps the heart, much above that and you get cooked. Used to have a sign at the physics lab where I worked showing those various regions.

 

Ohm's Law says I = E / R

 

I is current

E is voltage

R is resistance

 

So the amount of current that flows is determined both by the voltage present and by the resistance it must flow through. If resistance is constant, higher voltage will produce higher current.

 

Now this assumes that the source of the voltage can supply the voltage at any current, limited only by Ohm's law. In reality, all power supplies have a maximum current they can deliver into low resistances. This holds true for a computer power supply, a car battery, or a 9V Duracell.

 

So Ohm's Law is an abstraction that depends on various assumptions.

 

For instance, if you touch a 9V battery to a screwdriver shaft, which is nearly zero ohm resistance, the battery will get hot but there's not enough power there to melt the screwdriver because the battery has an internal resistance also and it will dominate when the external resistance is low.

 

Now try that with a car battery, or with a 220V 20Amp clothes dryer outlet, and you're going to see some serious results.

 

Terry D.

 

P.S. Conversely, a Van DeGraff generator may charge up to thousands (or even millions) of volts, but if you touch it you won't be killed because there simply isn't enough charge accumulated to sustain much current. Instead, the voltage will equalize between your body and the generator, and maybe your hair will stand on end - if you have any.

[Smilin' Bob]

So, how do you discharge a guitar amp or PA so it's safe to mess around with?

[mrbrown49]

 

So, how do you discharge a guitar amp or PA so it's safe to mess around with?

 

 

There are a couple ways to do it. Either, short the cap to ground, or connect the + and - of the cap to each other.

[el_tonto]

 

Either, short the cap to ground, or connect the + and - of the cap to each other.

 

 

... THROUGH A RESISTOR! Which you are holding with a pair of insulated pliers. Use a 1k to 10k, which will discharge even a large amp cap within one second.

 

If you short a fully-charged B+ cap with a screwdriver you will probably weld the screwdriver to the cap terminals (it's a bad weld; a little force will break your screwdriver free again), and if you've never done it before the loud crack and the flash of light will probably cause you to flinch (it's surprisingly frightening on a large cap!), which could lead to you touching some other non-discharged cap, or smacking your hand against the chassis which you might even cut yourself or something.

 

And never discharge it while holding a piece of wire to do the shorting, because then you've got a direct path from your hand to the cap terminals which would be charged at +400V compared to the chassis!

[kismet78]

 

... THROUGH A RESISTOR! Which you are holding with a pair of insulated pliers. Use a 1k to 10k, which will discharge even a large amp cap within one second. If you short a fully-charged B+ cap with a screwdriver you will probably weld the screwdriver to the cap terminals (it's a bad weld; a little force will break your screwdriver free again), and if you've never done it before the loud crack and the flash of light will probably cause you to flinch (it's surprisingly frightening on a large cap!), which could lead to you touching some other non-discharged cap, or smacking your hand against the chassis which you might even cut yourself or something. And never discharge it while holding a piece of wire to do the shorting, because then you've got a direct path from your hand to the cap terminals which would be charged at +400V compared to the chassis!

 

 

Do you have to do that to all of the caps individually?

[el_tonto]

 

Do you have to do that to all of the caps individually?

 

 

It depends on which parts of the circuit you are going to be working on. I'd have a schematic handy and from that would know which caps present a danger to me.

[ked]

Hello folks, first post. The danger inside an amp is the fact that it has high DC voltage. DC is extremely dangerous since it will stop your heart. That's why you're always told to work with only one hand at a time in the amp. This way DC can't go through one side of your body, through your heart to the other side of your body to a ground. You have a good chance of surviving a when it just goes in one hand.

 

 

Ken

[tocs100]

(Yes I searched...)

Got an amp with the ground prong broken off. If I plug it into a power strip which does have a ground prong, will that "ground" the amp?

 

(PS, looking for a Peavey Century 200 H amp head.)

[WRGKMC]

I think the original Post was asking Why do signs say Danger High Voltage, and not Danger High Current. This is a dummy factor. Most people know voltage deals with electricity. If they saw Danger High Current, They'd be looking around to see where the water flow was.

[tedmich]

death by electrocution with musical instrument equipment is very uncommon; a recent poll here at HC had almost no one who reported being killed.

 

In my experience, a Y chromosome highly correlates to believing you are in danger of dieing (or killing) at any given moment, irrespective of the actual probability.

 

[mrbrown49]

 

(Yes I searched...) Got an amp with the ground prong broken off. If I plug it into a power strip which does have a ground prong, will that "ground" the amp? (PS, looking for a Peavey Century 200 H amp head.)

 

 

No. Get your power cable fixed. It's cheap and easy.

[drewl]

Plenty of the rich and famous have been shocked by improperly grounded equipment like Keef Richards and Ace Frehley (Shock me!)

And most amps and any appliance for that matter have warning labels.

I've gotten nailed by 5,6 even 7 hundred volts from amps, kinda wakes you up but I usually do more damage flinging my arms/hands out of the way and banging them on stuff around me.

[PaoloJM]

 

I think the original Post was asking Why do signs say Danger High Voltage, and not Danger High Current. This is a dummy factor. Most people know voltage deals with electricity. If they saw Danger High Current, They'd be looking around to see where the water flow was.

 

 

I'd have thought it was more due to the fact that all high voltage circuits are "potentially" (pun intended) dangerous, whereas not all high current circuits are dangerous to human contact.

[WRGKMC]

I'd have thought it was more due to the fact that all high voltage circuits are "potentially" (pun intended) dangerous, whereas not all high current circuits are dangerous to human contact.

 

No its current thats dangerous. You can generate 20,000 volts of static electricity walking across a carpet and get zapped a littel but its not going to hurt you. Take a low voltage, High current, and good conductor path and you're dead meat.

 

 

"Hello folks, first post. The danger inside an amp is the fact that it has high DC voltage. DC is extremely dangerous since it will stop your heart".

 

 

This is not unique to DC voltage. AC can and does kill many more people than DC. As far as an amp goes, Turning a properly functioning amp off and letting it set awhile discharges most of the DC potential in the caps as it bleeds off through the circuitry. (Its still good to be safe discharging higv v caps than to be sorry).

With an amp unplugged the residual DC voltage left in a capacitor is static, not steady. Its discharge will give you a good blast but rarely kills because its not a steady source. (unless you have a weak heart and there is ideal grounding conditions)

 

If you consider an electric chair and how well the body needs to be is grounded and how the electrodes need to be are moistened, it gives you a better idea of what it takes to kill someone. I'm not by any means saying dont use proper percautions and work safely here, I'm just enhancing the topic a bit to separate fact from fiction.

 

From what some put up you would think you'd need rubber floves and a 20 foot pole to install flashloght batteries. On the other hand there are guys who climb onto live 40,000 volt transmission lines to repair them.

 

Why dont they get killed? Answer is - There needs to be a difference in potential and your body needs to be in the path of least resistance between the two potentials.

It doesnt have to be to ground either. A difference in volts of say one positive line being 100V and another positive being 200V is 100V. It has the same difference in potential between the two as the 100v to ground.

 

In theory, If you were insulated from ground, and connected a wire to a high voltage DC cap, and brought the voltage slowly up to 4 or 600 volts you would feel nothing. Let go of the wire and then touch bare ground and the discharge from your body to ground would kick your butt. Again a slow trickel charge back down to neutral ground and you'd feel nothing.

 

I've seen this done live using static generators back in my school days and I'm sure many have as well. I dont suggest anyone prooving anything by wiring themselves to an amp. But for those who do plan working with any kind of electricity for a living, you should learn the true facts of what electricity is, does and how it can be channeled and harnessed to be useful as well as dangerous.

[PaoloJM]

 

No its current thats dangerous. You can generate 20,000 volts of static electricity walking across a carpet and get zapped a littel but its not going to hurt you. Take a low voltage, High current, and good conductor path and you're dead meat.

 

 

Well I was refering to high voltage circuits, as in electrical circuits with a power source. I know current does the damage but it's the voltage in the circuit that drives the current through you.

 

Correct me if I'm wrong but take for example a low voltage circuit @ 24Vdc. If this circuit is low resistance, say 50ohms, then 480mA will flow through the circuit which is a reasonable amount of current and certainly capable of killing a human. However you, a human, present at least 1k ohm resistance typically (I measured 1.2M ohm between my index fingers last night for example). If you touch the 24Vdc part you only get 24mA at worst (assuming you are completing the circuit to ground and not to a significantly higher or lower reference), which is considered noticable but not dangerous. Therefore this high(ish) current circuit presents no appreciable danger.

[WRGKMC]

By the book with voltages being applied directly to the chest.

 

"At currents as low as 60 to 100 milliamperes, low-voltage (110-220 volts), 60-hertz alternating current traveling through the chest for a split second can cause life-threatening irregular heart rhythms. About 300-500 milliamperes of direct current is needed to have the same effect."

 

http://hypertextbook.com/facts/2000/JackHsu.shtml

 

I dont consider 480ma to be very high and probibly wouldnt be able to feel it in most cases. Given the resistance of the skin, and the length of both arms, the resistance of those arms, how much salt is in the blood (Water doesnt conduct electricity well its the impurities and salts suspended in the water that do) and how damp the skin is and part of the body that conducts the voltage that will determine how much current a body conducts.

I dont think many people set a amp chassis on their chest and turn it on which would be the ideal way to recieve such a jolt to stop a heart. I been shocked off raw AC sockets hundreds of times. An standard AC socket can provide up to 15 amps. Luckily I was never well grounded, standing in water etc to get the full current there that could be applied. (Otherwise I'd be typing this on the internet from the twilight zone). Usually it was a slip troubleshooting and the hand touched the wrong place and the voltage would pass across the hand to a frame and cause a very painful hand for several minuites or hours.

 

A 9V battery can put out around 300 MA for a short time. I you can test them with your toungue to see how strong the battery is. A littel bite with a new battery but theres no path across the heart muscle. If the skin on the chest was made very conductive with some conductive grease and you had a metal pad on the front and side of the heart. You could disrupt its rythum with low current depending on how much fat there is on the skin.

 

With a defribulator it requires between 200 and 1700 volts applied to the chest to restart a heart. They now commonly rate defribulators in Joules. Joules is used because its the "Deliverd" energy that is important, Not the source voltage and current.

[PaoloJM]

I think that you're missing the point I am making.

 

The circuit in my example could have had 4 ohms of resistance making it a 6 amp circuit, which is high current.

You would still only get, at most, 24mA of current through you if you acciedentally touch the +24Vdc line while grounded, which is harmless. So this high current circuit is harmless. A small DC motor might be like this.

 

The amount of current the supply is capable of sourcing/sinking is largely irrelevent, unless of course you get "stuck" on the circuit, in which case you will probably end up thoroughly barbequed in stead of just shocked.

 

The amount of current in the circuit itself is irrelevent. It's the potential for that current to flow through you instead of the rest of the circuit that is the problem, and that requires voltage.

[tedmich]

aside from defib killing you, its the IR^2 heating that hurts!

 

Resistance is futile, and painful!

[WRGKMC]

"The amount of current in the circuit itself is irrelevent".

 

Its highly relevent under certain conditions

 

It's the potential for that current to flow through you instead of the rest of the circuit that is the problem,

 

potential?

 

Kind of saying its there but its not. Potential isnt bad. Its the reality of it flowing thats important. Sounds like I'm parcing words, I am to a point, bear with me. I understand the statement in general terms and we are in agreement but the reality is the factor here.

 

Remember path of least resistance is what current is going to travel.

Voltage remains at the source as a potential between two poles.

If the circuit is active, a good deal of current is being consumed by the circuit already. A motor may be drawing most of the available current already because the coil is relatively low resistance. Touching the circuit may create a paralell path to ground or it may not.

Putting yourself In series with the source and ground presents the greatest danger. You would feel the full force of the current. In parallel, you wont feel the full current unless the resistance of your body is low enough to compete with the path the motor is providing.

 

Sitting here at work in the electronic repair shop here I pick up an ohm meter and read 2.5 Megohms thumb to thumb. Hands are dry and fingers caloused from guitar playing. Not a very good conductor in comparison to say a 100 ohm motor. II probibly wont feel a thing touching the circuit. Put me in series hand to hand with the motor things change drastically. The resistance of the motor is neglagable. I would recieve a much greater jolt while the motor stood still.

 

 

"and that requires voltage"

 

Kind of the chicken or the egg. Cant have voltage without current, cant have current without voltage. You also need a path. The better the path conducts the more the current flow. The conductance rating is resistance.

How much it impedes/conducts determines the amount of current.

Power supply source voltages usually remain the same weather its connected to a cuircuit or not. If I had to answer I would have to say I = V/R All are needed.

 

 

You can have a High "V" and a High "R" and a low "I" and feel littel or no current. You can have a low "R" say 1 ohm, and a low "V" say 1 volt. One divided by one equals one amp. It can kill you if the "I" is being applied directly to the heart.

 

If you have 1 volt devided by the 2.5Meg ohms I just measured hand to hand, you would have .00000004 amps. Not much zap there. 24 volts, same resistance, .0000096, still probibly cant feel it. 120v .000496 12,000v .048 amps now your getting dangerous.

 

 

Now I take the same meter, wet my fingers and squeeze the leads real hard.

and I get 50,000 ohms. At 24V I get .00048 amps at 120v I get .0024 amps

at 1200v I get .24 amps.

 

 

You see what I'm driving at here. Conditions vary greatly here depending on the resistance of the body. Being cool calm and collect has a huge difference in what may pass through the body. The area touched will as well. If you have a large area of the skin touched the resistance will be much lower than a small area. If the potential is there to cook through the skin then the resistance will drop and the current will go way up.

 

This wasnt real scientific, but the meter is bran new and it all follows ohms law.

 

Now heres a bonus question. Since I measured hand to hand to get my resistance reading, Would the current recieved by the heart with one hand half way across my chest be double or half the current?

 

Read carefully it may or may not be a trick question or a yes or no answer.

[PaoloJM]

 

Sitting here at work in the electronic repair shop here I pick up an ohm meter and read 2.5 Megohms thumb to thumb. Hands are dry and fingers caloused from guitar playing. Not a very good conductor in comparison to say a 100 ohm motor. II probibly wont feel a thing touching the circuit. Put me in series hand to hand with the motor things change drastically. The resistance of the motor is neglagable. I would recieve a much greater jolt while the motor stood still.

 

 

If i understand you correctly and you do somehow manage to put youself in series with the motor (extremely unlikely but let's continue) then your bodies resistance is added to the motors resistance and even less current flows through you than if you were in parallel with the motor.

 

 

Kind of the chicken or the egg. Cant have voltage without current, cant have current without voltage.

 

This statement is simply not true. An well regulated 24Vdc power supply will still measure close to 24Vdc whether there is a load or not. No load = no current but you can still meaure the voltage that is present.

 

 

If you have 1 volt devided by the 2.5Meg ohms I just measured hand to hand, you would have .00000004 amps. Not much zap there. 24 volts, same resistance, .0000096, still probibly cant feel it. 120v .000496 12,000v .048 amps now your getting dangerous. Now I take the same meter, wet my fingers and squeeze the leads real hard. and I get 50,000 ohms. At 24V I get .00048 amps at 120v I get .0024 amps at 1200v I get .24 amps.

 

 

This is simply supporting my point, it's the voltage that counts, not the current in the circuit and not the amount or the current the power supply is capable of delivering.

 

 

 

Now heres a bonus question. Since I measured hand to hand to get my resistance reading, Would the current recieved by the heart with one hand half way across my chest be double or half the current? Read carefully it may or may not be a trick question or a yes or no answer.

 

 

To answer this simply, it would be the same current, you are form a series circuit between both fingers and as we all know; current at any point in a series circuit is the same. However in reality the body does not exhitbit uniform resistance throughout, so more current may be directed through one path over another and in a largely unpredicatble manner.

[mike42]

I'm waitin for HIGH VOLTAGE II.

[WRGKMC]

If i understand you correctly and you do somehow manage to put youself in series with the motor (extremely unlikely but let's continue) then your bodies resistance is added to the motors resistance and even less current flows through you than if you were in parallel with the motor.

 

Paolo I'm sorry You'll Just have to go back and Study your basic ohms law. I dont think you were formally trained in electronics and dont understand basic electricity and how it flows through circuits. You seem to think Voltage does the work in a circuit which is distorting you're perception of how it works. I would start with electrons moving through a wire and the basic atomics and get a solid picture of what current, voltage and resistance is. Then work on with series parallel circuits and see how it does what it does.

 

I'm honestly not trying to be a putdown here, in fact I'm trying to be the least confrontative as possible in explaining some basics here. Maybe its my writing style I dont know, If it is try to look past that and understand the basic premis I'm trying to present here. I'm sure there are many who may not have strong fundamentals reading this and can benifit from the conversation we're having. Googeling up current flow in a series parallel circuit should bring up hundreds of examples of how ohms law works.

 

 

One other note I have to comment on is this one.

 

""This is simply supporting my point, it's the voltage that counts, not the current in the circuit and not the amount or the current the power supply is capable of delivering"".

 

Again you need all three, all three are dependant on each other. If one is missing, its not a complete circuit, or at best you could say its disfunctional.

 

Heres a simple description of voltage and current flow I was taught in my first electronic class back in high school.

 

Battery. The chemical makeup of a battery changes the atoms around one pole so the electrons in the atoms around the negative pole collect extra electrons. Around the positive pole the atoms loose electrons. They have atoms with holes so to say. How much "pressure or voltage" depends on the amount of electrons and holes available on each side. This can be due to the size of the plates, acid strength working upon the metals etc.

 

 

Current flow. When a path is provided from negative to positive electrons move from the negative side to the positive and the holes move from the positive to the negative side. The example in class used was a row of kids in chairs. The first chair (Positive) is vaccant. As current flows the person in the second seat, moves to the first chair and fills it, the vaccant chair moves back to the second position. The person in the 3rd seat moves to the second seat, the vaccant seat is now in the third seat, so on down the line until the battery dies and there are no more electrons or holes left.

 

The holes and electrons are equal and opposite. Its their movement that does the work and its their movement that can cause damage.

 

In the old way of explaining electricity, the pump is the battery. The pressure provided by the pump is the voltage, The movement of water passing through a pipe from the negative to positive is current. A narrowing of the pipe is the resistance.

 

OK without resistance in a circuit you have a short between negative and positive. in the case of a battery, You have maximum current flow until the to poles potentials are neutralized. What voltage is measured across the source is dependant on the resistance of the conductor, but lets say its zero resistance. You cant measure voltage without the internal resistance of a meter being less than the conductor, but the pressure will exist. (You can measure current with the meter in series but the meter introduces resistance). Both amps and voltage will drop evenly down as the battery discharges.

 

Put two resistors in series across the source. The current drop across the two equalize to the lowest of the two. The voltage is divided across the two. The sum of the two voltages equals the source, the current is the same current passing through both. If you have a high and a low resistance, the high resistance will recieve the greatest pressure, the one with low resistance easily passes the reduced current of the first.

 

In a parallel circuit, the voltage is the same across both, and the current splits. The total of the two loads equals the total current provided by the source.

The path of least resistance. With a high and low resistor, a resistor with "low" resistance (Good conductor) passes more current and has higher amps. A resistor with high resistance (Poor conductor) has lower amps.

 

Now we go back to your first statement.

 

" "If i understand you correctly and you do somehow manage to put youself in series with the motor (extremely unlikely but let's continue) then your bodies resistance is added to the motors resistance and even less current flows through you than if you were in parallel with the motor" ".

 

The total current that flows through you in a series is a mathamatical equasion. The low resistance of the motor is neglagable for dropping the total current so most will be available. The low resistance of the motor basically acts as a conductor. Your body has high resistance. It will be the restrictor in the flow determining most of the total current flow. The lower the resistance of the body the lower the voltage drop across the body, the greater the current flow through the both the body and the motor. Current flow will always be equal passing through both. The higher the resistence of one or both, the lower the current flow. The better the conductance of either or both, the higher the current. Zero resistance, and infinity being the two extremes.

 

In parallel its the opposite occurs for current. The path of least resistance is the motor, it will pass most of the current due to its low resistance. Putting the body with a high resistance in parallel has a lower current drop. Voltage remains the same across both. As the resistance of the body decreases(as it conducts better), the more current flow is removed from the motor and passed through the body. The current flow on the motor decreases as the current flow across the body increases. Voltage remains the same. When the resistance of the body equals the motor, the two will have equal current flow. If the bodys resistance continued to conduct better than the wire in the motor, the body would receive a greater share of current than the motor.

 

 

This is the simpelest way I can explain what happens. All three are needed to have a circuit, Ohms law is a natureal law involving trigonometry

Trigo meaning three. (I sucked at math by the way in earley school till I got into electronics where I was able to put a face on it. Then it all made sence to me) .

 

Lastly,

 

The answer to that question was indeed a trick answer. It stated only one hand so there was no current flow albiet the grounding that may have occured through the air or the soles of the shoes which I also specifically left out. the rest of it I'll leave alone except if one hand was grounded, There would be an equal amount of current across the entire body, not more in one area than another. If you go back to how current moves, The holes and electrons meet an pass each other at the point of maximum resistance/least conductance.