Arcam Amp

[The Natural Philosopher]

No, its the volts that cause the mills.

I have a 200A capable battery Of 12v. I have a 200ma battery of 12kV. In both case the potential power is the same.

You want to tell me that putting my had across a car battery is less safe that putting it across 12KV with the capability of feeding 100mA?

In that case, I'll cut one hand on each car battery terminal, and you can put one hand on each terminal of thee 12kV supply.

I wont have to argue with you any more then

I don't have to think about a statement that is so completely at odds with everything I have learned from experiece, been taught in classes, and is embodied in every single safety specification that exists to guard the stupid and ignorant from their own complete lack of understanding.

Utter bollox is succinct, cogent, and entirely accurate.

[Steve Firth]

Do you want to tell me that if I put my hand near (or on) a Van de Graaf generator at a potential of 450kV that I would not be safe?

Are you asserting that a 12V potential is sufficient to pass a current of 200A through the human body?

Are you asserting that 200ma can be passed safely through the human body?

BTW, 200mA at 12kV (DC) would probably not result in death.

Perhaps you ought to learn something about physics and physiology? You deserve that "Natural Philosphopher" tag about as much as you deserve "Emperor of France".

[Dave Liquorice]

Without the mills, the volts just hurt (a lot).

With that current capabilty either can kill, you are assuming that skin resistance is high thus 12v doesn't have the humph to get a killing current to flow. Skin resistance might not be high.

Now if the supply source impedance is high such that the current flow is limited to In that case, I'll cut one hand on each car battery terminal, and you

Make sure your hands are nice and wet with a good conducting solution.

Well your experience is flawed with the assumption that skin resistance is always high. It isn't. If it's just volts that kill how come people don't drop dead when they've walked across a dry nylon carpet and drawn a 1/2" arc from themselves to an earthed object?

[The Natural Philosopher]

Dont be a complete plonker.

YIu can dip your hand in slat solution, and a car battery wont kiill

The absolute lowest resistance I have ever measured grasping a pair of copper pipes with steay hands across my body is about 3K ohms.

So about 4mA max. In practice its a lot highert.

To get to say 15mA requires at least 36v. Which is why the law specifies something like 48V as being a voltage around which no great care need be taken.

Lethal shock below that is completely unknown.

You can get a pretty noticeable, but non lethal shock off e,g a 100W pA amps lousdpeaker output. That's about 100V p-to-p.

115AC, which is about 200v p-to-p is definitely lethal. Henc the use of split balanced 110v on power tools used onsite..to restrict shock to at worst case 50vAC wrt to earth

And your knowledge is flased wby not realising that skin resistance is irrelevant. The body itself has a huge internal resistance that cannot allow currents to develop no matter how low the skin resistance is.

>

[John Rumm]

been done with 9V though:

resistance is very much lower than the skins)

or not...

[Andy Champ]

This article talks about electrical safety for divers:

"A wet diver has a limb-to-limb resistance of approximately 500 ohms for voltages over 50, and 750 ohms for voltages less than 50."

That's a pretty good approximation to hand dipped in salt water. And

12v at 500 ohms is 24mA. You'd feel it, but it (probably) wouldn't kill you. I don't propose to try it though.

Yon sailor managed to get the electricity right into his blood...

Andy

[Mike]

So the law states it's perfectly safe to work on any 24v battery system then is it?

The 24v battery system I'm thinking of right now is about the size of a Ford Focus and with busbars many inches across.

[Dave Plowman (News)]

There's a big difference between burn or explosion risks and that of electrocution.

[Jules]

Drop a crowbar across 'em and you can answer that question for yourself ;)

[Man at B&Q]

Not into the same load.

Putting your hand across 12V is inherently safe in most normal circumstances. No matter what current the battery is rated at, you'll never get anywhere near enough to do you any harm due to the inpedance of your hand.

Depends on the impedance of the 12KV supply. The original point was with regard to high voltages from a high impedance supplies. You've twisted it into a high voltage battery which is presumably quite low impedance. 200mA at 12KV implies a load of 60Kohms. Is your battery capable of sustaining that same current through a smaller load (human hand)?

MBQ

[Andy Champ]

I'm always rather careful. I don't fancy losing my ring finger by cauterisation...

Andy

[The Natural Philosopher]

so what?

You may manage to melt a screwdriver. but without something to step the voltage up, you wont electrocute yourself.

[The Natural Philosopher]

Don't worry. The ring will be gone in a flash..

[Jon Fairbairn]

That reminds me of something we were told on a Marconi safety course. Someone was sent to paint a room containing a telephone exchange where there was a big bank of batteries (24V maybe? I can't remember). I suppose that because the busbars were uninsulated, the decorator believed they were "safe" (otherwise they would have been insulated, right?), a belief of which he was rapidly disabused when he used them as a shelf for his metal paint pail...

The other thing in that course was that we were told that

12V subcutaneously could be lethal. I think the anecdote that acompanied that was of a practical joke involving a car battery and two drawing pins, but it's an awfully long time since that course.

[Adrian]

That one's usually told about old-style telephone exchanges - where the voltage was 'only' 50v - but with an awful lot of amps behind it.....

Adrian

[Mike]

"Which is why the law specifies something like 48V as being a voltage around which no great care need be taken."

QED

[Jon Fairbairn]

They weren't "old style" when I was told it, they were stil current! And yes, it was probably 48V (assuming lead acid cells).

[Adrian]

And when I was working in those exchanges, too ! But 'old style' as in electromechanical - rather than this new-fangles computerised stuff

Certainly was.......

Adrian

[dennis]

The new ones have a power rack at the end of each suit. It has several AC-DC convertors and a pile of batteries. These feed a fuse board with lots of 10 mm2 feeds. The fuses spring up when they blow showering you with hot metal if someone has removed the shield.

When I started at GECT you were warned about metal watch straps.. if you forgot and put your wrist through the bus bars you lost your hand.

[Mike]

Believe me I know ! the quote "Which is why the law specifies something like 48V as being a voltage around which no great care need be taken." is about as misleading as the words of a politician.

Volts kill, amps kill, it doesn't necessarily need lots of volts or lots of amps, I still smile when recall many years ago hearing a mate working on a 12v powered VHF transmitter touch the 450v DC on the output valve. It didn't kill him but I fell off my chair laughing :)