Soft Start for Lathe?

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

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Harold_V
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Re: Soft Start for Lathe?

Post by Harold_V » Wed May 01, 2019 3:50 pm

Patio wrote:
Tue Apr 30, 2019 10:48 pm
Some say it only takes 1 amp across the heart (hand to hand or hand to foot) to end you.
I was told (high school electricity class) that the amperage is less-----much less. Mr. Madsen said 7 mils across the heart was enough to kill. Likely true, as the voltages and amperage in one's body are slight.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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BadDog
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Re: Soft Start for Lathe?

Post by BadDog » Wed May 01, 2019 4:01 pm

It depends on how it's introduced. I don't recall exact values, but if you stick a needle in each hand and hit it with very little amperage it can be fatal. But due to the insulating qualities of the skin and related tissues, you can do the same thing with medical leads and conductive gel on the skin, and you might not even feel the same amperage. On normal dry skin, higher limits still.
Russ
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Harold_V
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Re: Soft Start for Lathe?

Post by Harold_V » Wed May 01, 2019 4:05 pm

It's all related to Ohm's law. The higher the voltage, the better the chance that the lethal amount of amperage will be delivered.

The point is, it takes very little amperage to kill.

H
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Bill Shields
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Re: Soft Start for Lathe?

Post by Bill Shields » Wed May 01, 2019 4:05 pm

that number (7 MA) is something that the GFI manufacturers are well aware of (and accurate) , which is why the trip level on these things is so low (5MA).

I CAN (from on-the-job experience -> not my own), positively affirm that 200 amps @ 120 VDC will cook you like a hot dog and turn you into char - at which point having the heart stop is the least of your worries :(
Too many things going on to bother listing them.

John Hasler
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Re: Soft Start for Lathe?

Post by John Hasler » Wed May 01, 2019 4:16 pm

Harold_V wrote:
Wed May 01, 2019 3:50 pm
Patio wrote:
Tue Apr 30, 2019 10:48 pm
Some say it only takes 1 amp across the heart (hand to hand or hand to foot) to end you.
I was told (high school electricity class) that the amperage is less-----much less. Mr. Madsen said 7 mils across the heart was enough to kill. Likely true, as the voltages and amperage in one's body are slight.

H
It varies enormously from one individual to another. 5 ma was chosen as a safe upper limit.

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liveaboard
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Re: Soft Start for Lathe?

Post by liveaboard » Wed May 01, 2019 6:12 pm

Patio wrote:
Tue Apr 30, 2019 10:48 pm
Liveaboard, you friend is very lucky. The leakage in the drill press, had a high enough resistance that your friend may have felt nothing. I would also have questioned whether the unit was grounded.
If it was grounded, the GFI would always trip.
My friend died from a non-machine related issue, but that 380V 3-phase drill press is still in use.
Actually, I used it extensively myself in the past; never felt a thing.
Euro GFI's are usually (I think) 20mA*, but higher tolerances are available; people usually fit them to circuits that run old machines.
I've had a few zaps in my life; actually it's my earliest memory.
One time I was stuck to a 220V wire by a finger, earthed through bare feet on a dry floor.
I pulled the fitting off the wall to get free; there was a hole burned deep into my fingertip. That was pre-GFI days.
Remembering to shut off the power before working on the wiring is good practice.

*edit;
Standard ones are 4mA, 20mA are what people use to avoid replacing old machines that they should really replace.

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NP317
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Re: Soft Start for Lathe?

Post by NP317 » Thu May 02, 2019 10:53 am

New title for this thread: "Soft Restart For a Human Heart"

I spent 22 years working for Physio-Control Corporation, building, servicing and designing portable heart defibrillators, monitors, and other non-invasive medical monitoring devices.
Yes, the fatal current for human hearts is in the window of about 7 to 10 milliAmps.
External application of current (through the chest) to defibrillate a human heart can be anywhere from 50 Joules of energy, to 400 Joules.
Requirements depend on the person's body mass and structure.
For open heart defibrillation, there are special shaped "spoons" to cup the heart and deliver around 25 Joules of energy.
I have many stories from my years working with the users of those instruments.

It's amazing what you can learn here...
~RN

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