Electric arcs in arc welders

[geratheg]

Hello,

Previously I thought to make an arc through the air requires a very large voltage, but then saw arc welders can do this with lower voltages. How much is the current? I thought the voltage needs to be large enough to ionize air before making an arc. Correct me if I'm wrong.

Question unrelated to topic:
How much current does it take to get a burn? I accidentally got shocked with a 36V solar panel (60cell with 8.6amps max current ratings) with a burn blister across the ring finger on the right hand. I felt the shock and noticed the burn after. Maybe the burn was from the wires being shorted. Should I worry about this shock? Curious how the current travels across the body since it's like an infinite grid of resistors all packed together so current travels across the entire body, or not? Does this current reach the brain and cause any effect or damage to the brain?

[IanB]

Arc welders:

A high voltage is required to initiate a spark between two electrodes, but once the air is ionized the resistance drops dramatically and the arc can be sustained with a much lower voltage. In the case of arc welders you touch the electrode to the work to start things off and then draw the electrode away. The arc created contains ions of vaporized metal so it doesn't need much voltage to sustain a high current through that arc.

Electric burns:

Small burns to fingers and other peripheral parts are not much to worry about. The core of the body won't be affected. However, it is possible for an arc to burn a hole through your flesh and leave an internal injury that is not visible from outside. This will be bad for you, but is not likely to happen at low voltages like 36 V.

[Nerull]

You don't start arc welding from far away, you draw an arc by touching the electrode to the metal to be welded. Once an ionized air path is created its much easier for the arc to sustain itself. You can draw an arc with a 1.5v battery, though not a very big one.

Its generally with current limited supplies with adjustable current, anywhere from 0 to 200A depending on your electrode and what you are welding.

[geratheg]

Thanks for all the answers!

@IanB

How does electric shock at low-voltages affect the brain? Anything the worry about?
Which internal injuries are you referring to? Like if the burn occurred in a finger.

[T3sl4co1l]

Thanks for all the answers!

@IanB

How does electric shock at low-voltages affect the brain? Anything the worry about?
Which internal injuries are you referring to? Like if the burn occurred in a finger.

If you have to ask, maybe it's already done its job... 

J/K.

Internal injuries are more like... oh, you got ten amperes through your meat or veins?  Let's destroy some tissue.

Food for thought (literally); http://youtu.be/aUAkezGstlQ

Simply, if there's enough raw power delivered to cause temperature rise and internal injuries (burns, tissue destruction, later necrosis, and maybe worse things), you get secondary problems from that.

The most prominent immediate hazard is electrical disruption of the heart.  Burns are what happens when that doesn't (or isn't enough), or when your muscles contract and you get stuck.  Electrical disruption of the brain, I think, is a very low incidence thing; if you've ever seen electroshock therapy hardware, it looks pretty robust... the scalp isn't very conductive (because of the skull and dura mater, and maybe simply because... the brain is mostly greasy compounds, so maybe isn't all that conductive unless you get into the arteries?), so it's fairly powerful, considering that it ultimately doesn't have to do very much, electrically speaking.

Also, I don't think normal people are at much risk of anything electric in nature (besides heart problems, as I said).  If you're prone to seizures, that might be a risk factor and hazard for working on wires near your head or neck.  Other than that, no, I don't think the cranial risk is there.

Tim

[Psi]

Some welders, like TIG, have a high voltage generator built in, 20kv or so, which starts the arc automatically so you don't have to touch the tip to the metal.
TIG welding tips are very easy to contaminate so touching them to things is a big no no.

[geratheg]

If you have to ask, maybe it's already done its job... 

J/K.

Internal injuries are more like... oh, you got ten amperes through your meat or veins?  Let's destroy some tissue.

Food for thought (literally); http://youtu.be/aUAkezGstlQ

Simply, if there's enough raw power delivered to cause temperature rise and internal injuries (burns, tissue destruction, later necrosis, and maybe worse things), you get secondary problems from that.

The most prominent immediate hazard is electrical disruption of the heart.  Burns are what happens when that doesn't (or isn't enough), or when your muscles contract and you get stuck.  Electrical disruption of the brain, I think, is a very low incidence thing; if you've ever seen electroshock therapy hardware, it looks pretty robust... the scalp isn't very conductive (because of the skull and dura mater, and maybe simply because... the brain is mostly greasy compounds, so maybe isn't all that conductive unless you get into the arteries?), so it's fairly powerful, considering that it ultimately doesn't have to do very much, electrically speaking.

Also, I don't think normal people are at much risk of anything electric in nature (besides heart problems, as I said).  If you're prone to seizures, that might be a risk factor and hazard for working on wires near your head or neck.  Other than that, no, I don't think the cranial risk is there.

Tim

That gave me one of the biggest laughs 

Other than that, the amount of current that goes through the body is dependent on voltage and resistance. I was a bit sweaty, low resistance. But then it was across my finger so I guess it wasn't as dangerous as if two leads were across the body.
I guess I don't need to worry about any brain damage and other things.

I wonder why I felt a shock on the finger instead of just a burn, didn't think a low voltage like 36V would make me feel a shock. Was it because I was sweaty and current went through the finger; or was it because the wires shorted and I touched the wires with my finger when they shorted?

How many times have you been shocked and burned by a voltage like that?

[IanB]

I didn't think a low voltage like 36V would make me feel a shock.

Oh, it's not a low voltage. 24 V is already able to give you a good tingle, 36 V is in let's not touch this territory. If you have wet sweaty fingers, well you're in for quite a shock if you think 36 V is not going to affect you.

(Think about it, 36 V is about a third of 120 V, and from my last experiment 120 V across my fingers lead to a painful  moment. So what does a third of Ouch!!!! feel like?)

[geratheg]

Oh, it's not a low voltage. 24 V is already able to give you a good tingle, 36 V is in let's not touch this territory. If you have wet sweaty fingers, well you're in for quite a shock if you think 36 V is not going to affect you.

(Think about it, 36 V is about a third of 120 V, and from my last experiment 120 V across my fingers lead to a painful  moment. So what does a third of Ouch!!!! feel like?)

A third of ouch... LOL.

[Paul Moir]

TIG welding tips are very easy to contaminate so touching them to things is a big no no.

In some settings you have to turn your high frequency (high voltage) start off though because of EMI.  It's not an unusual protocol in hospitals.  Some I understand won't let you in the door with HF start, so you have to use scratch start TIG.

Scratch start TIG using a 12V lead acid battery (or sometimes 2) is a popular poor-man's rig.  Argon also makes forming the arc easier than in a nitrogen atmosphere. 

[cellularmitosis]

Some welders, like TIG, have a high voltage generator built in, 20kv or so, which starts the arc automatically so you don't have to touch the tip to the metal.
TIG welding tips are very easy to contaminate so touching them to things is a big no no.

Just to clarify for geratheg, those TIG welders just use high frequency, high voltage, low amperage to get the arc started, then the low voltage, 100+ amp arc takes over.

You'll hear welders refer to this as "high frequency start", but the important part is the high voltage.

[cellularmitosis]

How does electric shock at low-voltages affect the brain?

Some people even do it intentionally!  see and http://www.reddit.com/r/tDCS

[geratheg]

How does electric shock at low-voltages affect the brain?

Some people even do it intentionally!  see and http://www.reddit.com/r/tDCS

That looks crazy and interesting. Isn't the current regulated to be specific though? How high is the current from this intentional craziness compared to what I would experience across the brain from getting a shock across my finger? It seems as if the brain doesn't just fry or become too affected based on this.

[cellularmitosis]

usually seems to be 1 or 2mA.

[G7PSK]

With MMA (welding rods) the arc is maintained in an inert atmosphere produced by vaporising the flux coating which contains various additives to help start and maintain the arc, try welding after removing the flux coat or with a piece of plain wire as modern welding rods have additives in the alloy as well to help make the rod run smoother.
Most TIG units will have not only HF starts but something called lift tig as well, with this the tungsten is touched to the work piece but to avoid contamination only a few milli amps of current flow the main current being switched on automatically as  circuit is broken by lifting the tungsten from the work, and it is HF as that will start an arc much more easily than just a high voltage DC.

[cs.dk]

Just to chime in

When MIG welding in thin sheets the voltages are typically low ~17-22V. The wire shorts the transformer, and a drop is melting off. This is contact/dip transfer, and gives that typically "frying bacon" sound.
However, for high production in thicker materials, "spray transfer" happens above ~25V with argon rich gasses. The wire isn't touching the material before been melted off and throwed against the material.

[Zero999]

I didn't think a low voltage like 36V would make me feel a shock.

Oh, it's not a low voltage. 24 V is already able to give you a good tingle, 36 V is in let's not touch this territory. If you have wet sweaty fingers, well you're in for quite a shock if you think 36 V is not going to affect you.

(Think about it, 36 V is about a third of 120 V, and from my last experiment 120 V across my fingers lead to a painful  moment. So what does a third of Ouch!!!! feel like?)

That's a bit of a simplification.

120VAC is a hell of a lot more than three times as dangerous as 36VDC. For a start 120VAC is really 170V and AC currents are far more likely to cause muscle spasms and ventricular fibrillation, than DC.

36VDC is relatively safe and is unlikely to cause a severe shock, even if you're damp.

With solar panels the open circuit voltage is often much higher than the rated voltage by as much as 50% higher which makes 54V which can give you a bit of a belt if you're damp.

In this case it's probably more the burning which shocked you, than the electric current.

[max666]

Yes, the human body is basically an infinite resistor network, shaped in the for of a human 
And you could simulate how big the current density through the brain would be if you put x amps across your fingers, but I can tell you now it will be bugger all.

At 36 V, or maybe up to 54 V like Hero mentioned, I don't think you could get a burn on your finger from the current through your flesh alone. I think shorting wires and the resulting arc between the wires, burning your fingers from outside, is far more likely.
Hang on, let me walk the walk ...
Disclaimer: Don't try this at home, kids! Voltages above 50 V can be lethal in certain circumstances.
I put my two lab supplies in series and put 63 V across my dry ring finger (about 2 cm apart, but it's not very sensitive to distance). We're talking 0.15 mA, and 0.4 mA maximum if I really press on it and keep it on long enough. I didn't feel anything, so let's kick it up a notch. I wet my finger and grabbed the banana leads starting with 30 V. Current was already significantly higher but I was able to increase it up to 63 V with only feeling a slight tingle, we're talking 1 mA now. Surprisingly letting go of the banana leads felt like a tiny electric shock and in deed the initial grabbing or letting loose feels worse then a thigh grip. But no signs of burning anywhere near. This was DC and across one finger only.

[Seekonk]

A lot of farmers died with the old DELCO 32V 30HZ generators.  Usually because they were hot a sweaty when working on them.

[geratheg]

Yes, the human body is basically an infinite resistor network, shaped in the for of a human 
And you could simulate how big the current density through the brain would be if you put x amps across your fingers, but I can tell you now it will be bugger all.

At 36 V, or maybe up to 54 V like Hero mentioned, I don't think you could get a burn on your finger from the current through your flesh alone. I think shorting wires and the resulting arc between the wires, burning your fingers from outside, is far more likely.
Hang on, let me walk the walk ...
Disclaimer: Don't try this at home, kids! Voltages above 50 V can be lethal in certain circumstances.
I put my two lab supplies in series and put 63 V across my dry ring finger (about 2 cm apart, but it's not very sensitive to distance). We're talking 0.15 mA, and 0.4 mA maximum if I really press on it and keep it on long enough. I didn't feel anything, so let's kick it up a notch. I wet my finger and grabbed the banana leads starting with 30 V. Current was already significantly higher but I was able to increase it up to 63 V with only feeling a slight tingle, we're talking 1 mA now. Surprisingly letting go of the banana leads felt like a tiny electric shock and in deed the initial grabbing or letting loose feels worse then a thigh grip. But no signs of burning anywhere near. This was DC and across one finger only.

Bugger all- you mean nothing?
I was a little sweaty, so the infinite resistor network must have dropped resistance. Would the current density through the brain still be nothing?
Lol, now what would have happened if you didn't just wet your finger, but went outside and jogged until you were sweating. That would be different wouldn't it?

[Zero999]

Yes, the human body is basically an infinite resistor network, shaped in the for of a human 
And you could simulate how big the current density through the brain would be if you put x amps across your fingers, but I can tell you now it will be bugger all.

At 36 V, or maybe up to 54 V like Hero mentioned, I don't think you could get a burn on your finger from the current through your flesh alone. I think shorting wires and the resulting arc between the wires, burning your fingers from outside, is far more likely.
Hang on, let me walk the walk ...
Disclaimer: Don't try this at home, kids! Voltages above 50 V can be lethal in certain circumstances.
I put my two lab supplies in series and put 63 V across my dry ring finger (about 2 cm apart, but it's not very sensitive to distance). We're talking 0.15 mA, and 0.4 mA maximum if I really press on it and keep it on long enough. I didn't feel anything, so let's kick it up a notch. I wet my finger and grabbed the banana leads starting with 30 V. Current was already significantly higher but I was able to increase it up to 63 V with only feeling a slight tingle, we're talking 1 mA now. Surprisingly letting go of the banana leads felt like a tiny electric shock and in deed the initial grabbing or letting loose feels worse then a thigh grip. But no signs of burning anywhere near. This was DC and across one finger only.

Providing your hands are dry and the contact area it small you're pretty safe at that voltage.

Notice how grabbing and letting go was worse than the shock? This is due to the change in current affecting the nerves. Now imagine the shock if the polarity was being reversed at 50Hz.

A lot of farmers died with the old DELCO 32V 30HZ generators.  Usually because they were hot a sweaty when working on them.

But that's AC not DC so it's not surprising.

The regulations around the world vary slightly. Here in the UK, in dry/low risk areas, the user needs to be protected against direct contact with voltages above 25VAC or 60VDC so that farmyard 32VAC generator would need to be insulated, especially if there's a risk the regulator could fail, resulting in higher voltages.

Note that the 25VAC/60VDC limit is only in dry conditions where there's only a small area where the user can come into contact with the conductors. In damp areas, where there's a high risk of electrical shock, the voltage goes down to 12VAC or 30VDC.
https://www.tlc-direct.co.uk/Book/7.16.2.htm
http://www.premiersolutions.co.uk/images/17th%20Edition%20Regs.pdf

Bugger all- you mean nothing?
I was a little sweaty, so the infinite resistor network must have dropped resistance. Would the current density through the brain still be nothing?
Lol, now what would have happened if you didn't just wet your finger, but went outside and jogged until you were sweating. That would be different wouldn't it?

Unless one of the wires was on your head, then the current through your brain would be next to nothing.

If you were sweaty and in contact with a large conductor area (more likely wearing a ring) then yes it's possible the current would've been high enough to cause a shock but very unlikely to cause burns or be lethal. The burn would've been due to the heating in the conductor.

I've burnt myself before when I short circuited a NiCad cell by holding a wire to it with my thumb. Some of the insulation had come away from the cathode so the wire short circuited it, the wire glowed red hot and burned me. It was a very shocking experience, even though the voltage as under 1.2V, far to low for an electric shock.

[geratheg]

Thanks for the replies! I think I understand how arc welding works.

So the burn from the current causing heat also feels like an electric shock?

As for current through the brain even though I was sweating, I guess I won't be worrying about brain damage, memory loss, etc. anymore. Lol I probably exaggerated the shock and became paranoid.

[T3sl4co1l]

Bugger all- you mean nothing?
I was a little sweaty, so the infinite resistor network must have dropped resistance. Would the current density through the brain still be nothing?
Lol, now what would have happened if you didn't just wet your finger, but went outside and jogged until you were sweating. That would be different wouldn't it?

The main difference is the resistance of that outer layer of "infinite resistors".  The skin.  That's why you can grab multimeter probes (dry) and read megs, or casually brush against 120V and feel a buzz rather than a jolt.  Once it gets inside, the resistance is pretty low (~~ 100 ohms), which is why it takes a lot of current to physically cook you.  Also, with such low resistance, it only takes a few lucky paths to disrupt the heart, and arteries/veins are more conductive than muscle or fat layers.

Tim

[geratheg]

The main difference is the resistance of that outer layer of "infinite resistors".  The skin.  That's why you can grab multimeter probes (dry) and read megs, or casually brush against 120V and feel a buzz rather than a jolt.  Once it gets inside, the resistance is pretty low (~~ 100 ohms), which is why it takes a lot of current to physically cook you.  Also, with such low resistance, it only takes a few lucky paths to disrupt the heart, and arteries/veins are more conductive than muscle or fat layers.

Tim

Is it easier for it to get inside when you are sweaty?

[ConKbot]

I've burnt myself before when I short circuited a NiCad cell by holding a wire to it with my thumb. Some of the insulation had come away from the cathode so the wire short circuited it, the wire glowed red hot and burned me. It was a very shocking experience, even though the voltage as under 1.2V, far to low for an electric shock.

Ive done the same before.  Was putzing with a rechargeable AA, and a LED, shorted across the top with the LED lead, and my finger on it.  Square indented burn in my finger tip, and it smelled pretty foul too.  High current low voltage DC sources can be as dangerous or more dangerous than even mains, at least when it comes to metallic objects that the user is holding/wearing because of the risk of thermal burns, and the object welding itself in place. 

[Zero999]

Is it easier for it to get inside when you are sweaty?

Yes. The skin is porous and sweat is a very good conductor.

Ive done the same before.  Was putzing with a rechargeable AA, and a LED, shorted across the top with the LED lead, and my finger on it.  Square indented burn in my finger tip, and it smelled pretty foul too.

I did exactly the same thing!

High current low voltage DC sources can be as dangerous or more dangerous than even mains, at least when it comes to metallic objects that the user is holding/wearing because of the risk of thermal burns, and the object welding itself in place.

Especially when there's batteries which can blow up. Always use a fuse, as near to the battery as possible, when powering a circuit from large batteries.

[geratheg]

Touched battery terminals across my hand with thumb and index finger. Why can't I think ahead about the consequences lol    I touched them for no apparent reason other than to kill boredom without thinking I'd have current running through my body lol.
This time barely no feeling of a tingle from 12V battery, but still feel stupid for not thinking what I'm doing...

Anyway, what's the resistance across a dry finger? My meter reads it in the Mohms range, though Google says it should be in the Kohms range and with dry skin about 100Kohms.

[SeanB]

I have drawn nearly meter long arcs with a standard arc welder, doing welding of steel. Just need still air and you can draw a pretty big though short lived arc out of them.

Was changing UPS batteries, and was asked to do it live.  No ways, I get shocked enough with the trays as is just lifting them in with dry skin and was not going to add 340VDC on top of the 170V bus half voltage. You cannot help but get some contact when you lift a 50kg box to load it in the slot, especially with the terminals being aligned with the sides.

[tautech]

Thanks for the replies! I think I understand how arc welding works.

Be aware only one reply has stated the correct facts of how an arc is maintained.

With MMA (welding rods) the arc is maintained in an inert atmosphere produced by vaporising the flux coating which contains various additives to help start and maintain the arc, try welding after removing the flux coat or with a piece of plain wire as modern welding rods have additives in the alloy as well to help make the rod run smoother.

The sheiding of the arc and weld pool is of the utmost importance for good welds.
Try welding outside in a strong wind and you will find out.
This is when Mig is useless. 

To confuse matters more there are different types of electrode construction for AC, DC straight (electrode Negative) and DC reverse (electrode Positive).
Droplet transfer is improved when welding with DC straight as it mimicks electron flow. (- to +)

Then there are rods optimised for some welding positions and techniques. (Vertical uphand or downhand, Overhead, Cutting, Stove pipe, Overlays etc)
Plus the myriad of different metal types that can be welded.

But none of this is any different to safe practice with anything electrical......
Avoid wet conditions
Wear insulating footwear
Heavy Gloves can be useful for changing rods with a welder that bites (some do, especially high OC voltage models)
Work technique that mimimises the chance of electrical shock. (Methodology)

These days full body cover is the accepted norm when welding, on some sites electricians must cover up too.

I'd say take note of these modern workplace practises to keep yourself safe.